An Etymological Dictionary of Astronomy and Astrophysics

A method allowing for a simplified solution to the
→ radiative transfer equation
at frequencies of spectral lines in media moving with a high velocity gradient. This method assumes that the macroscopic velocity gradients are more important than local random variations of thermal line width: dv/dr > v_th/l, where dv/dr is the velocity gradient, v_th is the thermal broadening of the line, and l the length scale. The Sobolev approximation is only valid if the conditions of the gas do not change over the → Sobolev length. Under the Sobolev approximation, each point in the medium is isolated from other points, and the → radiative transfer problem becomes a local one and therefore much easier to solve.

See also: Named after the Russian astronomer Viktor Viktorovich Sobolev,
Moving Envelopes of Stars [in Russian], Leningr. Gos. Univ., Leningrad (1947) [translated by S. Gaposchkin, Harvard Univ. Press, Cambridge, Mass. (1960)]; → approximation.

A method allowing for a simplified solution to the
→ radiative transfer equation
at frequencies of spectral lines in media moving with a high velocity gradient. This method assumes that the macroscopic velocity gradients are more important than local random variations of thermal line width: dv/dr > v_th/l, where dv/dr is the velocity gradient, v_th is the thermal broadening of the line, and l the length scale. The Sobolev approximation is only valid if the conditions of the gas do not change over the → Sobolev length. Under the Sobolev approximation, each point in the medium is isolated from other points, and the → radiative transfer problem becomes a local one and therefore much easier to solve.

See also: Named after the Russian astronomer Viktor Viktorovich Sobolev,
Moving Envelopes of Stars [in Russian], Leningr. Gos. Univ., Leningrad (1947) [translated by S. Gaposchkin, Harvard Univ. Press, Cambridge, Mass. (1960)]; → approximation.

In the → Sobolev approximation, the length over which the conditions of the gas do not change and
the approximation is valid. It is expressed by: l_s = v_th/(dv/dr), where v_th is the thermal line width and (dv/dr) the velocity gradient. In other words, the length over which the profile function of a line is shifted through a distance equal to its own width by the macroscopic velocity gradients that exist in the moving medium.

See also: → Sobolev approximation; → length.

In the → Sobolev approximation, the length over which the conditions of the gas do not change and
the approximation is valid. It is expressed by: l_s = v_th/(dv/dr), where v_th is the thermal line width and (dv/dr) the velocity gradient. In other words, the length over which the profile function of a line is shifted through a distance equal to its own width by the macroscopic velocity gradients that exist in the moving medium.

See also: → Sobolev approximation; → length.

Of or pertaining to human society.

See also: → society; → -al.

Of or pertaining to human society.

See also: → society; → -al.

A continuing process whereby an individual acquires a personal identity and learns the norms, values, behavior, and social skills appropriate to his or her social position (Dictionary.com).

See also: → socialize; → -tion.

A continuing process whereby an individual acquires a personal identity and learns the norms, values, behavior, and social skills appropriate to his or her social position (Dictionary.com).

See also: → socialize; → -tion.

To make social; make fit for life in companionship with others (Dictionary.com).

See also: → social; → -ize.

To make social; make fit for life in companionship with others (Dictionary.com).

See also: → social; → -ize.

Of or pertaining to social groups, their activities, or to social relations.

Etymology (EN): From societ-, from → society, + → -al.

Etymology (PE): Hazâni, from hazân-, from hazâné, → society,

• -i, → -al.

Of or pertaining to social groups, their activities, or to social relations.

Etymology (EN): From societ-, from → society, + → -al.

Etymology (PE): Hazâni, from hazân-, from hazâné, → society,

• -i, → -al.

An organized group of persons associated together for scientific, cultural,
or other purposes; e.g. a physical society. See also:
→ associate, → association,
→ dissociate, → dissociation, → social, → socialization, → socialize, → societal.

Etymology (EN): M.E., from O.Fr. societe, from L. societatem (nominative societas), from socius “companion,” → associate.

Etymology (PE): Hazâné, from Av. hacenay- “getting together, association,” from verb hac-, hax- “to associate, follow, accompany”
(haxay-, hašy-, haš- “friend”), hacaiti “follows;”
hacā “from, out of;” O.Pers. hacā “from” (Mid.Pers. hac “from;” Mod.Pers. az “from”);
PIE base *sek^w- “to follow;” cf. Skt. sac- “to be associated or united with,” sácate “accompanies, follows,” sácā “with;” Gk. hepesthai “to follow;” L. sequi “to follow.”

An organized group of persons associated together for scientific, cultural,
or other purposes; e.g. a physical society. See also:
→ associate, → association,
→ dissociate, → dissociation, → social, → socialization, → socialize, → societal.

Etymology (EN): M.E., from O.Fr. societe, from L. societatem (nominative societas), from socius “companion,” → associate.

Etymology (PE): Hazâné, from Av. hacenay- “getting together, association,” from verb hac-, hax- “to associate, follow, accompany”
(haxay-, hašy-, haš- “friend”), hacaiti “follows;”
hacā “from, out of;” O.Pers. hacā “from” (Mid.Pers. hac “from;” Mod.Pers. az “from”);
PIE base *sek^w- “to follow;” cf. Skt. sac- “to be associated or united with,” sácate “accompanies, follows,” sácā “with;” Gk. hepesthai “to follow;” L. sequi “to follow.”

The science or study of the origin, development, organization, and functioning of human society; the science of the fundamental laws of social relations, institutions, etc. (Dictionary.com).

See also: → society; → -logy.

The science or study of the origin, development, organization, and functioning of human society; the science of the fundamental laws of social relations, institutions, etc. (Dictionary.com).

See also: → society; → -logy.

Of or pertaining to Socrates or his philosophy, followers, etc.,
→ Socratic irony, → Socratic method.

Etymology (EN): Socrates (469?-399 B.C.), Athenian philosopher.

Of or pertaining to Socrates or his philosophy, followers, etc.,
→ Socratic irony, → Socratic method.

Etymology (EN): Socrates (469?-399 B.C.), Athenian philosopher.

A means by which the pretended ignorance of a skillful questioner leads the person answering to expose his own ignorance (Collins).

See also: → Socratic; → irony.

A means by which the pretended ignorance of a skillful questioner leads the person answering to expose his own ignorance (Collins).

See also: → Socratic; → irony.

The use of questions, as employed by Socrates, to develop a latent idea, as in the mind of a pupil, or to elicit admissions, as from an opponent, tending to establish a proposition (Dictionary.com).

See also: → Socratic; → method.

The use of questions, as employed by Socrates, to develop a latent idea, as in the mind of a pupil, or to elicit admissions, as from an opponent, tending to establish a proposition (Dictionary.com).

See also: → Socratic; → method.

A metallic chemical element; symbol Na (L. natrium]. Atomic number 11; atomic weight 22.98977; melting point 97.81°C; boiling point 892.9°C; specific gravity 0.971 at 20°C. It was discovered in 1807 by the English chemist Humphry Davy from electrolysis of caustic soda (NaOH).

See also: Sodium, from soda (NaOH).

A metallic chemical element; symbol Na (L. natrium]. Atomic number 11; atomic weight 22.98977; melting point 97.81°C; boiling point 892.9°C; specific gravity 0.971 at 20°C. It was discovered in 1807 by the English chemist Humphry Davy from electrolysis of caustic soda (NaOH).

See also: Sodium, from soda (NaOH).

The → sodium tail of the Moon as it appears in the sky opposite the Sun. The SMS undergoes changes in shape and brightness. It is brighter when the → new moon occurs at → perigee, when the new moon is north of the → ecliptic, and approximately five hours after the new moon.

See also: → sodium; → Moon; → spot.

The → sodium tail of the Moon as it appears in the sky opposite the Sun. The SMS undergoes changes in shape and brightness. It is brighter when the → new moon occurs at → perigee, when the new moon is north of the → ecliptic, and approximately five hours after the new moon.

See also: → sodium; → Moon; → spot.

1. A kind of → cometary tail appearing in some → comets, such as → Hale-Bopp. Sodium tails arise from the very strong → fluorescence of their sodium atom → D lines in the visible. They are rapidly accelerated to high velocities by the Sun, forming a very straight tail distinct from the → ion tail. The release mechanism of sodium from comets is still a matter of debate. Also called → neutral tail.
   

2. → sodium tail of the Moon.
   

3. A comet-like tail of Mercury similar to that of the Moon, but much longer, stretching up to 3.5 million km.

See also: → sodium; → tail.

1. A kind of → cometary tail appearing in some → comets, such as → Hale-Bopp. Sodium tails arise from the very strong → fluorescence of their sodium atom → D lines in the visible. They are rapidly accelerated to high velocities by the Sun, forming a very straight tail distinct from the → ion tail. The release mechanism of sodium from comets is still a matter of debate. Also called → neutral tail.
   

2. → sodium tail of the Moon.
   

3. A comet-like tail of Mercury similar to that of the Moon, but much longer, stretching up to 3.5 million km.

See also: → sodium; → tail.

A comet-like tail of the Moon comprised of → sodium (Na) atoms and invisible to the naked eye.

The lunar surface is constantly bombarded by the → solar wind, → photons, and → meteoroids, which can liberate Na atoms from the → regolith. These atoms are subsequently accelerated by solar → radiation pressure to form a long comet-like tail opposite the Sun. Near → new moon, this diffuse cloud of Na atoms encounters the Earth’s gravity and is “pinched” into a beam of enhanced density. This beam appears as the ~3° diameter Sodium Moon Spot (SMS) seen in the sky opposite the Sun. The spot is about five times the diameter of the → full moon, and is 50 times fainter than can be seen with the unaided eye. The spot is reflected light from millions of Na atoms that two days earlier were on the surface of the Moon. This spot is visible to sensitive cameras equipped with filters tuned to the orange light emitted by Na atoms near 589.3 nm (Baumgardner et al., 2021 Journal of Geophysical Research: Planets DOI: 10.1029/2020je006671).

See also: → sodium; → tail; → Moon.

A comet-like tail of the Moon comprised of → sodium (Na) atoms and invisible to the naked eye.

The lunar surface is constantly bombarded by the → solar wind, → photons, and → meteoroids, which can liberate Na atoms from the → regolith. These atoms are subsequently accelerated by solar → radiation pressure to form a long comet-like tail opposite the Sun. Near → new moon, this diffuse cloud of Na atoms encounters the Earth’s gravity and is “pinched” into a beam of enhanced density. This beam appears as the ~3° diameter Sodium Moon Spot (SMS) seen in the sky opposite the Sun. The spot is about five times the diameter of the → full moon, and is 50 times fainter than can be seen with the unaided eye. The spot is reflected light from millions of Na atoms that two days earlier were on the surface of the Moon. This spot is visible to sensitive cameras equipped with filters tuned to the orange light emitted by Na atoms near 589.3 nm (Baumgardner et al., 2021 Journal of Geophysical Research: Planets DOI: 10.1029/2020je006671).

See also: → sodium; → tail; → Moon.

General: Delicate in texture, grain, or fiber.
Not bright or glaring.
Physics: Of a beam of particles or electromagnetic radiation, having relatively low energy, as opposed to → hard. → soft X-rays

Etymology (EN): M.E. softe “yielding, gentle, mild;” O.E. softe “gentle, easy;” cf. O.S. safti, O.H.G. semfti, Ger. sanft, M.Du. sachte, Du. zacht.

Etymology (PE): Narm “soft; smooth; mild,” from Mid.Pers. narm “soft; humble.”

General: Delicate in texture, grain, or fiber.
Not bright or glaring.
Physics: Of a beam of particles or electromagnetic radiation, having relatively low energy, as opposed to → hard. → soft X-rays

Etymology (EN): M.E. softe “yielding, gentle, mild;” O.E. softe “gentle, easy;” cf. O.S. safti, O.H.G. semfti, Ger. sanft, M.Du. sachte, Du. zacht.

Etymology (PE): Narm “soft; smooth; mild,” from Mid.Pers. narm “soft; humble.”

In → stellar dynamics studies of → three-body encounters, a → binary system whose → binding energy is smaller than the typical → kinetic energy of the relative motion of an incoming third body. See also → hard binary.

See also: → soft; → binary.

In → stellar dynamics studies of → three-body encounters, a → binary system whose → binding energy is smaller than the typical → kinetic energy of the relative motion of an incoming third body. See also → hard binary.

See also: → soft; → binary.

A member of a small class of objects which emit intense bursts of → gamma rays and → X-rays (> 100 keV) at irregular intervals. The bursts last for some 100 milli-seconds. It is conjectured that they are → magnetars. See also → starquake.

See also: → soft; → gamma rays; → repeater.

A member of a small class of objects which emit intense bursts of → gamma rays and → X-rays (> 100 keV) at irregular intervals. The bursts last for some 100 milli-seconds. It is conjectured that they are → magnetars. See also → starquake.

See also: → soft; → gamma rays; → repeater.

Same as → soft gamma repeater (SGR).

See also: → soft; → gamma ray; → repeater.

Same as → soft gamma repeater (SGR).

See also: → soft; → gamma ray; → repeater.

Iron that has a low carbon content, in contrast to → steel. Because it is easily magnetized and demagnetized, it is used to make the cores of → solenoids and other electrical equipment.

See also: → soft; → iron.

Iron that has a low carbon content, in contrast to → steel. Because it is easily magnetized and demagnetized, it is used to make the cores of → solenoids and other electrical equipment.

See also: → soft; → iron.

The back, muscular (not bony) part of the roof of the → mouth in front of the → pharynx.

See also: → soft; → palate.

The back, muscular (not bony) part of the roof of the → mouth in front of the → pharynx.

See also: → soft; → palate.

An → X-ray binary system that has a long period of → quiescence interrupted by → outbursts of low-energy → soft X-rays. Alternatively known as X-ray novae, the majority (~ 75%) of SXTs contain a → black hole and a low-mass → main sequence  → companion star in orbit around one another.
It is thought that SXTs arise in a similar manner to → dwarf novae, through instabilities in the → accretion disk around the → compact object (→ disk instability model).

See also: → soft; → X-ray;
→ transient..

An → X-ray binary system that has a long period of → quiescence interrupted by → outbursts of low-energy → soft X-rays. Alternatively known as X-ray novae, the majority (~ 75%) of SXTs contain a → black hole and a low-mass → main sequence  → companion star in orbit around one another.
It is thought that SXTs arise in a similar manner to → dwarf novae, through instabilities in the → accretion disk around the → compact object (→ disk instability model).

See also: → soft; → X-ray;
→ transient..

X-ray photons with energies between about 0.1 to 10 keV. → hard X-rays.

See also: → soft; → X-rays.

X-ray photons with energies between about 0.1 to 10 keV. → hard X-rays.

See also: → soft; → X-rays.

A general term used to describe a collection of computer programs, procedures, and documentation that perform some tasks on a computer system. → hardware.

Etymology (EN): → soft + ware, from M.E., from O.E. waru, from P.Gmc. *waro (cf. Swed. vara, Dan. vare, M.Du. were, Du. waar, Ger. Ware “goods”).

Etymology (PE): Narm, → soft + afzâr “instrument, means, tool,” from Mid.Pers. afzâr, abzâr, awzâr “instrument, means,” Proto-Iranian *abi-cāra- or *upa-cāra-, from cāra-, cf. Av. cārā- “instrument, device, means” (Mid.Pers. câr, cârag “means, remedy;” loaned into Arm. aucar, aucan “instrument, remedy;” Mod.Pers. câré “remedy, cure, help”), from kar- “to do, make, build;” kərənaoiti “he makes” (Pers. kardan, kard- “to do, to make”); cf. Skt. kr- “to do, to make,” krnoti “he makes, he does,” karoti “he makes, he does,” karma “act, deed;” PIE base k^wer- “to do, to make”).

A general term used to describe a collection of computer programs, procedures, and documentation that perform some tasks on a computer system. → hardware.

Etymology (EN): → soft + ware, from M.E., from O.E. waru, from P.Gmc. *waro (cf. Swed. vara, Dan. vare, M.Du. were, Du. waar, Ger. Ware “goods”).

Etymology (PE): Narm, → soft + afzâr “instrument, means, tool,” from Mid.Pers. afzâr, abzâr, awzâr “instrument, means,” Proto-Iranian *abi-cāra- or *upa-cāra-, from cāra-, cf. Av. cārā- “instrument, device, means” (Mid.Pers. câr, cârag “means, remedy;” loaned into Arm. aucar, aucan “instrument, remedy;” Mod.Pers. câré “remedy, cure, help”), from kar- “to do, make, build;” kərənaoiti “he makes” (Pers. kardan, kard- “to do, to make”); cf. Skt. kr- “to do, to make,” krnoti “he makes, he does,” karoti “he makes, he does,” karma “act, deed;” PIE base k^wer- “to do, to make”).

The overall structure of a software system consisting of mutually dependent components that create a logical whole.

See also: → software; → architecture.

The overall structure of a software system consisting of mutually dependent components that create a logical whole.

See also: → software; → architecture.

All loose, unconsolidated earth and organic materials above bedrock that support plant growth.

Etymology (EN): M.E. soile, O.Fr. soil “piece of ground, place,” from L. solium “seat,” meaning confused with that of L. solum “soil, ground.”

Etymology (PE): Xâk, from Mid.Pers. xâk “earth, dust,” ultimately from Proto-Ir. *āika-, from *āi- “earth, soil,” cf. Av. āi- “earth, soil,” Gk. aia “earth, land,” + suffix -ka. The initial x- is a prothesis, as in xâya “egg” (Gershevitch 1962).

All loose, unconsolidated earth and organic materials above bedrock that support plant growth.

Etymology (EN): M.E. soile, O.Fr. soil “piece of ground, place,” from L. solium “seat,” meaning confused with that of L. solum “soil, ground.”

Etymology (PE): Xâk, from Mid.Pers. xâk “earth, dust,” ultimately from Proto-Ir. *āika-, from *āi- “earth, soil,” cf. Av. āi- “earth, soil,” Gk. aia “earth, land,” + suffix -ka. The initial x- is a prothesis, as in xâya “egg” (Gershevitch 1962).

The solar day on Mars, which has a mean period of 24 hours 39 minutes 35.244 seconds (based on SI units), about 2.7% longer than Earth’s solar day. The Martian sidereal day, as measured with respect to the fixed stars, is 24h 37m 22.663s, as compared with 23h 56m 04.0905s for Earth.

See also: Sol, from L. sol “sun,” cognate with Pers. hur, → Sun.

The solar day on Mars, which has a mean period of 24 hours 39 minutes 35.244 seconds (based on SI units), about 2.7% longer than Earth’s solar day. The Martian sidereal day, as measured with respect to the fixed stars, is 24h 37m 22.663s, as compared with 23h 56m 04.0905s for Earth.

See also: Sol, from L. sol “sun,” cognate with Pers. hur, → Sun.

Of or pertaining to the Sun.

See also: Adjective from L. sol; → Sun.

Of or pertaining to the Sun.

See also: Adjective from L. sol; → Sun.

→ solar photospheric abundance, → solar system abundance.

See also: → solar; → abundance.

→ solar photospheric abundance, → solar system abundance.

See also: → solar; → abundance.

The general term for all forms of short-lived phenomena on the Sun, including → solar flares, → sunspots, → prominences, etc., indicating that the Sun is an active star.

See also: → solar; → activity.

The general term for all forms of short-lived phenomena on the Sun, including → solar flares, → sunspots, → prominences, etc., indicating that the Sun is an active star.

See also: → solar; → activity.

Same as the → solar cycle.

See also: → solar activity; → cycle.

Same as the → solar cycle.

See also: → solar activity; → cycle.

A member of a class of unevolved or slightly evolved → Population I disk stars with an → effective temperature, degree of evolution, → metallicity, and kinematic property not very different from those of the Sun. See also → solar-like star; → solar twin.

See also: → solar; → analogue.

A member of a class of unevolved or slightly evolved → Population I disk stars with an → effective temperature, degree of evolution, → metallicity, and kinematic property not very different from those of the Sun. See also → solar-like star; → solar twin.

See also: → solar; → analogue.

The apparent direction (in the constellation → Columbia) away from which the Sun is moving in its orbit around the center of the Galaxy. → solar apex.

See also: → solar; → antapex.

The apparent direction (in the constellation → Columbia) away from which the Sun is moving in its orbit around the center of the Galaxy. → solar apex.

See also: → solar; → antapex.

The point on the celestial sphere toward which the Sun is apparently moving relative to the → local standard of rest. Its position, in the constellation → Hercules, is approximately R.A. 18h, Dec. +30°, close to the star → Vega. The velocity of this motion is estimated to be about 19.4 km/sec (about 4. AU/year). As a result of this motion, stars seem to be converging toward a point in the opposite direction, the → solar antapex.

See also: → solar; → apex.

The point on the celestial sphere toward which the Sun is apparently moving relative to the → local standard of rest. Its position, in the constellation → Hercules, is approximately R.A. 18h, Dec. +30°, close to the star → Vega. The velocity of this motion is estimated to be about 19.4 km/sec (about 4. AU/year). As a result of this motion, stars seem to be converging toward a point in the opposite direction, the → solar antapex.

See also: → solar; → apex.

The angle between the Sun’s → rotation axis and perpendicular to the → ecliptic plane. In other words, the inclination of the Sun’s → equator with respect to the → ecliptic plane. It is 7.25 degrees.

See also: → solar; → axial; → tilt.

The angle between the Sun’s → rotation axis and perpendicular to the → ecliptic plane. In other words, the inclination of the Sun’s → equator with respect to the → ecliptic plane. It is 7.25 degrees.

See also: → solar; → axial; → tilt.

A calendar based on the apparent yearly motion of the Sun on the → celestial sphere. The year is usually reckoned with respect to the → vernal equinox, approximately for example in the case of the → Gregorian calendar and accurately in the case of the → Iranian calendar.

See also: → solar; → calendar.

A calendar based on the apparent yearly motion of the Sun on the → celestial sphere. The year is usually reckoned with respect to the → vernal equinox, approximately for example in the case of the → Gregorian calendar and accurately in the case of the → Iranian calendar.

See also: → solar; → calendar.

The amount of solar radiation in all wavelengths received per unit of time per unit of area on a theoretical surface perpendicular to the Sun’s rays and at Earth’s mean distance from the Sun. Its mean value is 1367.7 W m^-2 or 1.37 × 10⁶ erg sec^-1 cm^-2. In other words, the solar constant is the mean → solar irradiance on the outer atmosphere when the Sun and Earth are spaced at 1 → astronomical unit. See also: → solar luminosity.

See also: → solar; → constant.

The amount of solar radiation in all wavelengths received per unit of time per unit of area on a theoretical surface perpendicular to the Sun’s rays and at Earth’s mean distance from the Sun. Its mean value is 1367.7 W m^-2 or 1.37 × 10⁶ erg sec^-1 cm^-2. In other words, the solar constant is the mean → solar irradiance on the outer atmosphere when the Sun and Earth are spaced at 1 → astronomical unit. See also: → solar luminosity.

See also: → solar; → constant.

The outermost atmosphere of the Sun immediately above the → chromosphere, which can be seen during a total solar eclipse. It consists of hot (1-2 × 10⁶ K), extremely tenuous gas (about 10^-16 g cm^-3) extending for millions of kilometer from the Sun’s surface.

See also: → solar; → corona.

The outermost atmosphere of the Sun immediately above the → chromosphere, which can be seen during a total solar eclipse. It consists of hot (1-2 × 10⁶ K), extremely tenuous gas (about 10^-16 g cm^-3) extending for millions of kilometer from the Sun’s surface.

See also: → solar; → corona.

The periodic variation in frequency or number of solar active events (→ sunspots, → prominences, → flares, and other solar activity) occurring with an interval of about 11 years. The solar cycle was discovered in 1843 by Samuel Heinrich Schwabe (1789-1875), a German apothecary and amateur astronomer, who after 17 years of observations noticed a periodic variation in the average number of sunspots seen from year to year on the solar disk. Solar cycle numbering goes back to the 18-th century, when the Cycle 1 peak occurred in 1760. Cycle 23 peaked in 2000, and the following Cycle 24 will reach its maximum in 2013.

See also: → solar; → cycle.

The periodic variation in frequency or number of solar active events (→ sunspots, → prominences, → flares, and other solar activity) occurring with an interval of about 11 years. The solar cycle was discovered in 1843 by Samuel Heinrich Schwabe (1789-1875), a German apothecary and amateur astronomer, who after 17 years of observations noticed a periodic variation in the average number of sunspots seen from year to year on the solar disk. Solar cycle numbering goes back to the 18-th century, when the Cycle 1 peak occurred in 1760. Cycle 23 peaked in 2000, and the following Cycle 24 will reach its maximum in 2013.

See also: → solar; → cycle.

The length of time between two successive transits of the Sun over the same meridian.

See also: → solar; → day.

The length of time between two successive transits of the Sun over the same meridian.

See also: → solar; → day.

The → angle between the → sea horizon, the → center of → Earth, and the center of the → solar disk.

See also: → solar; → depression.

The → angle between the → sea horizon, the → center of → Earth, and the center of the → solar disk.

See also: → solar; → depression.

The apparent shape of the → Sun’s → photosphere.

See also: → solar; → disk.

The apparent shape of the → Sun’s → photosphere.

See also: → solar; → disk.

A model for explaining the generation of the → solar magnetic field and the related observational features (mainly → solar cycle, → Sporer’s law, → Hale’s law, → Joy’s law, → polarity reversal). The global frame of this model is the interaction between a → turbulent plasma in the → convective zone (reciprocal generation of magnetic and electric fields) and the solar differential rotation (mutual transformation of meridional magnetic field into azimuthal magnetic field). The idea that a dynamo is responsible for generating the solar magnetic field was first proposed by Larmor (1919) and further developed by Cowling (1933), Parker (1955) and others.

See also: → solar; → dynamo.

A model for explaining the generation of the → solar magnetic field and the related observational features (mainly → solar cycle, → Sporer’s law, → Hale’s law, → Joy’s law, → polarity reversal). The global frame of this model is the interaction between a → turbulent plasma in the → convective zone (reciprocal generation of magnetic and electric fields) and the solar differential rotation (mutual transformation of meridional magnetic field into azimuthal magnetic field). The idea that a dynamo is responsible for generating the solar magnetic field was first proposed by Larmor (1919) and further developed by Cowling (1933), Parker (1955) and others.

See also: → solar; → dynamo.

An eclipse in which the Earth passes through the shadow cast by the Moon. Solar eclipses only happen when the Moon is new and when the Moon lies close to the node of its orbit.

See also: → solar; → eclipse.

An eclipse in which the Earth passes through the shadow cast by the Moon. Solar eclipses only happen when the Moon is new and when the Moon lies close to the node of its orbit.

See also: → solar; → eclipse.

The greatest angular distance from a → lunar orbit node
within which a → solar eclipse may occur when the Sun and Moon are in conjunction there. The solar ecliptic limit extends about 17° on each side of the node.

See also: → solar; → ecliptic; → limit.

The greatest angular distance from a → lunar orbit node
within which a → solar eclipse may occur when the Sun and Moon are in conjunction there. The solar ecliptic limit extends about 17° on each side of the node.

See also: → solar; → ecliptic; → limit.

In ancient astronomy, the difference between the Sun’s mean and actual position. The ancients observed that, although the motion of the Sun in the ecliptic is almost uniform, it is subject to a small annual variation.

See also: → solar; → equation.

In ancient astronomy, the difference between the Sun’s mean and actual position. The ancients observed that, although the motion of the Sun in the ecliptic is almost uniform, it is subject to a small annual variation.

See also: → solar; → equation.

A bright eruption form the Sun’s → chromosphere in the vicinity of a → sunspot. Solar flares are caused by tremendous explosions on the surface of the Sun. In a matter of just a few minutes they heat the material to many millions of degrees and release as much energy as a billion → megatons of → T.N.T..

See also: → solar; → flare.

A bright eruption form the Sun’s → chromosphere in the vicinity of a → sunspot. Solar flares are caused by tremendous explosions on the surface of the Sun. In a matter of just a few minutes they heat the material to many millions of degrees and release as much energy as a billion → megatons of → T.N.T..

See also: → solar; → flare.

An instrument especially designed for solar observations.

See also: → solar; → instrument.

An instrument especially designed for solar observations.

See also: → solar; → instrument.

The radiative power per unit area in all wavelengths from the Sun received by the Earth at its average distance from the Sun. Its mean value is called the → solar constant. The solar irradiance changes over a year by about 6.6% due to the variation in the Earth/Sun distance. Moreover, solar activity variations cause irradiance changes of up to 1%.

See also: → solar; → irradiance.

The radiative power per unit area in all wavelengths from the Sun received by the Earth at its average distance from the Sun. Its mean value is called the → solar constant. The solar irradiance changes over a year by about 6.6% due to the variation in the Earth/Sun distance. Moreover, solar activity variations cause irradiance changes of up to 1%.

See also: → solar; → irradiance.

The edge of the → disk of the → Sun.

See also: → solar; → limb.

The edge of the → disk of the → Sun.

See also: → solar; → limb.

The ecliptic longitude of the Sun. It varies from 0° (at the vernal equinox) to 360° during the year. By Kepler’s Second Law, the rate of change of the solar longitude is such that the Earth sweeps out equal areas on the ecliptic plane in equal times.

See also: → solar; → longitude.

The ecliptic longitude of the Sun. It varies from 0° (at the vernal equinox) to 360° during the year. By Kepler’s Second Law, the rate of change of the solar longitude is such that the Earth sweeps out equal areas on the ecliptic plane in equal times.

See also: → solar; → longitude.

The total → radiant energy, in all wavelengths,
emitted by the Sun in all directions. It is 3.828 × 10²⁶ W or 3.828 × 10³³ erg sec^-1 (International Astronomical Union, Resolution B3, 14 August 2015, Honolulu, USA). This is the luminosity unit conventionally used to give the luminosities of stars. See also: → solar constant.
When the Earth first formed, 4.56 billion years ago, the Sun radiated 30% less energy than it does today, thus giving rise to the so-called → faint early Sun paradox. Ever since then, its power has increased by 7% every billion years (I. Ribas, 2009, arXiv:0911.4872).

See also: → solar; → luminosity.

The total → radiant energy, in all wavelengths,
emitted by the Sun in all directions. It is 3.828 × 10²⁶ W or 3.828 × 10³³ erg sec^-1 (International Astronomical Union, Resolution B3, 14 August 2015, Honolulu, USA). This is the luminosity unit conventionally used to give the luminosities of stars. See also: → solar constant.
When the Earth first formed, 4.56 billion years ago, the Sun radiated 30% less energy than it does today, thus giving rise to the so-called → faint early Sun paradox. Ever since then, its power has increased by 7% every billion years (I. Ribas, 2009, arXiv:0911.4872).

See also: → solar; → luminosity.

The period of time, about 22 years, after which the magnetic → polarity of the Sun returns to its earlier state. It consists of two consecutive → solar cycles.

See also: → solar; → magnetic; → cycle.

The period of time, about 22 years, after which the magnetic → polarity of the Sun returns to its earlier state. It consists of two consecutive → solar cycles.

See also: → solar; → magnetic; → cycle.

The Sun’s magnetic field which is probably created by the → differential rotation of the Sun together with the movement of charged particles in the → convective zone. Understanding how the solar magnetic field comes about is the fundamental problem of Solar Physics. The solar magnetic field is responsible for all solar magnetic phenomena, such as → sunspots, → solar flares, → coronal mass ejections, and the → solar wind. The solar magnetic fields are observed from the → Zeeman broadening of spectral lines, → polarization effects on radio emission, and from the channeling of charged particles into visible → coronal streamers. The strength of Sun’s average magnetic field is 1 → gauss (twice the average field on the surface of Earth, around 0.5 gauss), and can be as strong as 4,000 Gauss in the neighborhood of a large sunspot.

See also: → solar; → magnetic; → field.

The Sun’s magnetic field which is probably created by the → differential rotation of the Sun together with the movement of charged particles in the → convective zone. Understanding how the solar magnetic field comes about is the fundamental problem of Solar Physics. The solar magnetic field is responsible for all solar magnetic phenomena, such as → sunspots, → solar flares, → coronal mass ejections, and the → solar wind. The solar magnetic fields are observed from the → Zeeman broadening of spectral lines, → polarization effects on radio emission, and from the channeling of charged particles into visible → coronal streamers. The strength of Sun’s average magnetic field is 1 → gauss (twice the average field on the surface of Earth, around 0.5 gauss), and can be as strong as 4,000 Gauss in the neighborhood of a large sunspot.

See also: → solar; → magnetic; → field.

The amount of mass in our Sun, 1.99 x 10³³ g, about 330,000 times the Earth’s mass. The solar mass is also the unit in which the masses of other stars,
galaxies, and other large celestial bodies are expressed.

See also: → solar; → mass.

The amount of mass in our Sun, 1.99 x 10³³ g, about 330,000 times the Earth’s mass. The solar mass is also the unit in which the masses of other stars,
galaxies, and other large celestial bodies are expressed.

See also: → solar; → mass.

The month(s) during the 11 year → solar cycle when the number of → sunspots reaches a maximum.

See also: → solar; → maximum.

The month(s) during the 11 year → solar cycle when the number of → sunspots reaches a maximum.

See also: → solar; → maximum.

The proportion of the solar matter made up of → chemical elements heavier than → helium. It is denoted by Z, which represents
the sum of all elements heavier than → helium, in mass fraction. The most recent determination of the solar Z gives a value of 0.0134 (Asplund et al. 2009, ARAA 47, 481), corresponding to the present-day photospheric composition.

See also: → solar; → metallicity.

The proportion of the solar matter made up of → chemical elements heavier than → helium. It is denoted by Z, which represents
the sum of all elements heavier than → helium, in mass fraction. The most recent determination of the solar Z gives a value of 0.0134 (Asplund et al. 2009, ARAA 47, 481), corresponding to the present-day photospheric composition.

See also: → solar; → metallicity.

The month(s) during the 11 year → solar cycle when the number of → sunspots is lowest.

See also: → solar; → minimum.

The month(s) during the 11 year → solar cycle when the number of → sunspots is lowest.

See also: → solar; → minimum.

The cloud of interstellar gas and dust from which the Sun and the rest of the solar system initially formed.

See also: → solar; → nebula.

The cloud of interstellar gas and dust from which the Sun and the rest of the solar system initially formed.

See also: → solar; → nebula.

That part of the Milky Way galaxy lying near the Sun. In fact there is no definition of the exact radius of this region. It is referred to the immediate solar neighborhood (within about 5 pc), the solar neighborhood (within about 25 pc), and the extended solar neighborhood (within a few hundred pc).

See also: → solar; → neighborhood.

That part of the Milky Way galaxy lying near the Sun. In fact there is no definition of the exact radius of this region. It is referred to the immediate solar neighborhood (within about 5 pc), the solar neighborhood (within about 25 pc), and the extended solar neighborhood (within a few hundred pc).

See also: → solar; → neighborhood.

A neutrino generated in the → Sun. The main source of solar neutrinos is the → proton-proton chain of reactions: 4 × p→ He + 2e⁺ + 2ν_e, in which an energy of +28 MeV is shared between the reaction products. These are called → low-energy neutrinos. There are less important reactions in the Sun yielding a smaller flux of higher energy neutrinos. The solar neutrino flux can be estimated from the → solar luminosity (L), as follows Since there are two neutrinos for each 28 MeV of energy, the neutrino flux at the Earth distance (d) is given by:

ν flux = 2Lsun/(28 MeV) × (1/4πd²) = 6 × 10¹⁰ cm^-2 s^-1. See also the → solar neutrino problem.

See also: → solar; → neutrino; → flux.

A neutrino generated in the → Sun. The main source of solar neutrinos is the → proton-proton chain of reactions: 4 × p→ He + 2e⁺ + 2ν_e, in which an energy of +28 MeV is shared between the reaction products. These are called → low-energy neutrinos. There are less important reactions in the Sun yielding a smaller flux of higher energy neutrinos. The solar neutrino flux can be estimated from the → solar luminosity (L), as follows Since there are two neutrinos for each 28 MeV of energy, the neutrino flux at the Earth distance (d) is given by:

ν flux = 2Lsun/(28 MeV) × (1/4πd²) = 6 × 10¹⁰ cm^-2 s^-1. See also the → solar neutrino problem.

See also: → solar; → neutrino; → flux.

A major discrepancy between the flux of neutrinos detected at Earth from the solar core and that predicted by current models of solar nuclear fusion and our understanding of neutrinos themselves. The problem, lasting from the mid-1960s to about 2002, was a considerably lesser detected number of neutrons compared with theoretical predictions. The discrepancy has since been resolved by new understanding of neutrino physics, requiring a modification of the → standard model of particle physics, in particular → neutrino oscillation.

See also: → solar; → neutrino;
→ problem.

A major discrepancy between the flux of neutrinos detected at Earth from the solar core and that predicted by current models of solar nuclear fusion and our understanding of neutrinos themselves. The problem, lasting from the mid-1960s to about 2002, was a considerably lesser detected number of neutrons compared with theoretical predictions. The discrepancy has since been resolved by new understanding of neutrino physics, requiring a modification of the → standard model of particle physics, in particular → neutrino oscillation.

See also: → solar; → neutrino;
→ problem.

A measure of the flux of neutrinos from the Sun reaching the Earth. 1 SNU is equal to 10^-36 solar neutrinos captured per target atom per second.

See also: → solar; → neutrino;
→ unit.

A measure of the flux of neutrinos from the Sun reaching the Earth. 1 SNU is equal to 10^-36 solar neutrinos captured per target atom per second.

See also: → solar; → neutrino;
→ unit.

A → European Space Agency (ESA) mission with strong → National Aeronautics and Space Administration (NASA) participation aimed at studying the Sun up close and from high latitudes, launched on 10 February 2020. Solar Orbiter is equipped with 10 instruments and will provide the first images of the Sun’s poles.

It will make a close approach of the Sun every six
months. Its distance from the Sun varies from within the orbit of
→ <i><a class="linkVoir" href="/terms/mercury/">Mercury</a></i>
to close to the orbit of Earth.
At closest approach, Solar Orbiter will be about approximately 42 million
km from the Sun. 

Solar Orbiter will combine in situ measurements of the
→ <i><a class="linkVoir" href="/terms/solar-wind/">solar wind</a></i>
around the spacecraft with remote sensing, looking at the Sun's
features from afar, to connect the two together. 

The spacecraft has been tested to withstand temperatures up to
500 °C -- enduring thirteen times the amount of solar heating
that satellites in Earth's orbit experience. 

Solar Orbiter will help us understand how our star creates and
controls the → <i><a class="linkVoir" href="/terms/heliosphere/">heliosphere</a></i>, i.e. 
the giant bubble of → <i><a class="linkVoir" href="/terms/plasma/">plasma</a></i>
that surrounds the whole → <i><a class="linkVoir" href="/terms/solar-system/">Solar System</a></i>
and influences the planets within it.

See also: → solar; → orbiter.

A → European Space Agency (ESA) mission with strong → National Aeronautics and Space Administration (NASA) participation aimed at studying the Sun up close and from high latitudes, launched on 10 February 2020. Solar Orbiter is equipped with 10 instruments and will provide the first images of the Sun’s poles.

It will make a close approach of the Sun every six
months. Its distance from the Sun varies from within the orbit of
→ <i><a class="linkVoir" href="/terms/mercury/">Mercury</a></i>
to close to the orbit of Earth.
At closest approach, Solar Orbiter will be about approximately 42 million
km from the Sun. 

Solar Orbiter will combine in situ measurements of the
→ <i><a class="linkVoir" href="/terms/solar-wind/">solar wind</a></i>
around the spacecraft with remote sensing, looking at the Sun's
features from afar, to connect the two together. 

The spacecraft has been tested to withstand temperatures up to
500 °C -- enduring thirteen times the amount of solar heating
that satellites in Earth's orbit experience. 

Solar Orbiter will help us understand how our star creates and
controls the → <i><a class="linkVoir" href="/terms/heliosphere/">heliosphere</a></i>, i.e. 
the giant bubble of → <i><a class="linkVoir" href="/terms/plasma/">plasma</a></i>
that surrounds the whole → <i><a class="linkVoir" href="/terms/solar-system/">Solar System</a></i>
and influences the planets within it.

See also: → solar; → orbiter.

The angle subtended (8’’.79) by the → equatorial radius of the Earth at a distance of 1 → astronomical unit.

See also: → solar; → parallax.

The angle subtended (8’’.79) by the → equatorial radius of the Earth at a distance of 1 → astronomical unit.

See also: → solar; → parallax.

The abundance of a → chemical element as determined from the observation of solar → spectral lines. The solar chemical composition is an important ingredient in our understanding of the formation, structure and evolution of both the Sun and our solar system. Furthermore, it is an essential reference standard against which the elemental contents of other astronomical objects are compared (Asplund et al. 2009, arXiv:0909.0948). The photospheric abundances relative to hydrogen are not representative of the → protosun, or global → solar system abundances.
This is because heavy-element fractionation in the Sun has altered photospheric abundances (Lodders 2003, ApJ 591, 1220).

See also: → solar; → photospheric; → abundance.

The abundance of a → chemical element as determined from the observation of solar → spectral lines. The solar chemical composition is an important ingredient in our understanding of the formation, structure and evolution of both the Sun and our solar system. Furthermore, it is an essential reference standard against which the elemental contents of other astronomical objects are compared (Asplund et al. 2009, arXiv:0909.0948). The photospheric abundances relative to hydrogen are not representative of the → protosun, or global → solar system abundances.
This is because heavy-element fractionation in the Sun has altered photospheric abundances (Lodders 2003, ApJ 591, 1220).

See also: → solar; → photospheric; → abundance.

The branch of astrophysics concerned with the study of the physical properties of the Sun based on the most
detailed observations which can be obtained for a star.

See also: → solar; → physics.

The branch of astrophysics concerned with the study of the physical properties of the Sun based on the most
detailed observations which can be obtained for a star.

See also: → solar; → physics.

Any power obtained by converting solar radiation into useful power.

See also: → solar; → power.

Any power obtained by converting solar radiation into useful power.

See also: → solar; → power.

A space probe designed to gather data about the Sun.

See also: → solar; → probe.

A space probe designed to gather data about the Sun.

See also: → solar; → probe.

A large, arch-shaped filament of hot gas extending outward from the Sun’s surface.
More at → prominence.

See also: → solar; → prominence.

A large, arch-shaped filament of hot gas extending outward from the Sun’s surface.
More at → prominence.

See also: → solar; → prominence.

All the constituents making up the Sun’s emission: photons, electrons, protons, neutrinos, and atomic nuclei.

See also: → solar; → radiation.

All the constituents making up the Sun’s emission: photons, electrons, protons, neutrinos, and atomic nuclei.

See also: → solar; → radiation.

The → radiation pressure of solar photons, which pushes a comet’s dust outward to form a → dust tail.

See also: → solar; → radiation; → pressure.

The → radiation pressure of solar photons, which pushes a comet’s dust outward to form a → dust tail.

See also: → solar; → radiation; → pressure.

Plural form of → solar radius.

See also: → solar; → radii.

Plural form of → solar radius.

See also: → solar; → radii.

A unit of length, representing the radius of the → Sun, used to express the size of stars in astrophysics. It is equivalent to: 695,700 km, 0.00465047 → astronomical units, 7.35355 &times 10^-8 → light-years, and 2.32061 → light-seconds.

See also: → solar; → radius.

A unit of length, representing the radius of the → Sun, used to express the size of stars in astrophysics. It is equivalent to: 695,700 km, 0.00465047 → astronomical units, 7.35355 &times 10^-8 → light-years, and 2.32061 → light-seconds.

See also: → solar; → radius.

The motion of the Sun around an axis which is roughly perpendicular to the plane of the → ecliptic; the Sun’s rotational axis is tilted by 7.25° from perpendicular to the ecliptic. It rotates in the → counterclockwise direction (when viewed from the north), the same direction that the planets rotate (and orbit around the Sun). The Sun’s rotation is differential, i.e. the period varies with latitude on the Sun (→ differential rotation). Equatorial regions rotate in about 25.6 days. The regions at 60 degrees latitude rotate more slowly, in about 30.9 days.

See also: → solar; → rotation.

The motion of the Sun around an axis which is roughly perpendicular to the plane of the → ecliptic; the Sun’s rotational axis is tilted by 7.25° from perpendicular to the ecliptic. It rotates in the → counterclockwise direction (when viewed from the north), the same direction that the planets rotate (and orbit around the Sun). The Sun’s rotation is differential, i.e. the period varies with latitude on the Sun (→ differential rotation). Equatorial regions rotate in about 25.6 days. The regions at 60 degrees latitude rotate more slowly, in about 30.9 days.

See also: → solar; → rotation.

A space vehicle designed to orbit about the Sun.

See also: → solar; → satellite.

A space vehicle designed to orbit about the Sun.

See also: → solar; → satellite.

The spectrum of the Sun’s electromagnetic radiation, consisting of a continuum spectrum marked with dark absorption lines.

See also: → solar; → spectrum.

The spectrum of the Sun’s electromagnetic radiation, consisting of a continuum spectrum marked with dark absorption lines.

See also: → solar; → spectrum.

The collective name for the Sun and all objects gravitationally bound to it. These objects are the eight planets, their 166 known moons, five dwarf planets, and billions of small bodies. The small bodies include asteroids, icy Kuiper belt objects, comets, meteoroids, and interplanetary dust. The solar system is roughly a sphere with a radius greater than 100,000 AU.
Planets, satellites, and all interplanetary material together comprise only about 1/750 of the total mass. Geochemical dating methods show that the solar system chemically isolated itself from the rest of the Galaxy (4.7 ± 0.1) × 10⁹ years ago.

See also: → solar; → system.

The collective name for the Sun and all objects gravitationally bound to it. These objects are the eight planets, their 166 known moons, five dwarf planets, and billions of small bodies. The small bodies include asteroids, icy Kuiper belt objects, comets, meteoroids, and interplanetary dust. The solar system is roughly a sphere with a radius greater than 100,000 AU.
Planets, satellites, and all interplanetary material together comprise only about 1/750 of the total mass. Geochemical dating methods show that the solar system chemically isolated itself from the rest of the Galaxy (4.7 ± 0.1) × 10⁹ years ago.

See also: → solar; → system.

Same as → protosolar abundance.

See also: → solar system; → abundance.

Same as → protosolar abundance.

See also: → solar system; → abundance.

A telescope designed so that heating effects produced by the Sun do not distort the images.

See also: → solar; → telescope.

A telescope designed so that heating effects produced by the Sun do not distort the images.

See also: → solar; → telescope.

The time based on the rotation of the Earth relative to the Sun. → mean solar time.

See also: → solar; → time.

The time based on the rotation of the Earth relative to the Sun. → mean solar time.

See also: → solar; → time.

A structure used in solar observations in order to raise the equipment above the
atmospheric disturbances caused by solar heating of the ground and the radiation of the heat into the atmosphere.

See also: → solar; → tower.

A structure used in solar observations in order to raise the equipment above the
atmospheric disturbances caused by solar heating of the ground and the radiation of the heat into the atmosphere.

See also: → solar; → tower.

An ideal star possessing fundamental physical parameters (mass, chemical composition, age, effective temperature, luminosity, gravity, magnetic fields, equatorial rotation, etc.) very similar, if not identical, to those of the Sun. See also → solar analog; → solar-like star.

See also: → solar; → twins paradox.

An ideal star possessing fundamental physical parameters (mass, chemical composition, age, effective temperature, luminosity, gravity, magnetic fields, equatorial rotation, etc.) very similar, if not identical, to those of the Sun. See also → solar analog; → solar-like star.

See also: → solar; → twins paradox.

The rate of change of the Sun’s position with respect to the local standard of rest toward the → solar apex.

See also: → solar; → velocity.

The rate of change of the Sun’s position with respect to the local standard of rest toward the → solar apex.

See also: → solar; → velocity.

A mass outflow, consisting of protons, electrons, and other subatomic particles, expelled constantly from the solar corona at about 500 km per second.
The solar mass-loss rate in this phenomenon amounts to about 2 x 10^-14 solar masses per year, or about 10⁶ tons per second. → stellar wind.

See also: → solar; → wind.

A mass outflow, consisting of protons, electrons, and other subatomic particles, expelled constantly from the solar corona at about 500 km per second.
The solar mass-loss rate in this phenomenon amounts to about 2 x 10^-14 solar masses per year, or about 10⁶ tons per second. → stellar wind.

See also: → solar; → wind.

The period of time required for the Earth to make one complete revolution around the Sun. Solar year is a general term for: → tropical year, → vernal equinox year, and → autumnal equinox year, which have different lengths.

See also: → solar; → year.

The period of time required for the Earth to make one complete revolution around the Sun. Solar year is a general term for: → tropical year, → vernal equinox year, and → autumnal equinox year, which have different lengths.

See also: → solar; → year.

A member of a very broad class of stars in which is found a mixture of late F, early, middle, and, sometimes, late G type dwarfs and sub-giants. See also → solar analog; → solar twin.

See also: → solar; → -like;
→ star.

A member of a very broad class of stars in which is found a mixture of late F, early, middle, and, sometimes, late G type dwarfs and sub-giants. See also → solar analog; → solar twin.

See also: → solar; → -like;
→ star.

Any of the various phenomena observable on the Earth that are caused by the influence of the Sun, such as aurora borealis.

See also: → solar; → terrestrial; → phenomenon.

Any of the various phenomena observable on the Earth that are caused by the influence of the Sun, such as aurora borealis.

See also: → solar; → terrestrial; → phenomenon.

A criterion for → convective stability in → massive stars. The Solberg-Høiland stability criterion corresponds to the inclusion of the effect of → rotation (variation of → centrifugal force) in the convective stability criterion. It is a combination of → Ledoux’s criterion (or possibly → Schwarzschild’s criterion) and → Rayleigh’s criterion. Both the dynamical shear and Solberg-Høiland instabilities occur in the case of a very large → angular velocity decrease outwards.

Therefore, in a → rotating star the Ledoux or Schwarzschild criteria for convective instability should be replaced by the Solberg-Høiland criterion. More specifically, this criterion accounts for the difference of the centrifugal force for an adiabatically displaced fluid element.

It is also known as the axisymmetric baroclinic instability. It arises when the net force (gravity + buoyancy + centrifugal force) applied to a fluid parcel in an adiabatical displacement has components only in the direction of the displacement (A. Maeder, Physics, Formation and Evolution of Rotating Stars, 2009, Springer).

See also: E. Høiland, 1939, On the Interpretation and Application of the Circulation Theorems of V. Bjerknes. Archiv for mathematik og naturvidenskab. B. XLII. Nr. 5. Oslo.

H. Solberg, 1936 (reprint), Le mouvement d’inertie de l’atmosphere stable et son rôle dans la théorie des cyclones.

H. Solberg, 1941, On the Stability of the Circular Vortex. Avhandl. utg. av Det Norske Videnskaps-Akademi i Oslo. I. Mat-Naturv. Klasse. No. 11.

Wasiutynski, J. 1946, Astrophysica Norvegica, 4, 1.

A criterion for → convective stability in → massive stars. The Solberg-Høiland stability criterion corresponds to the inclusion of the effect of → rotation (variation of → centrifugal force) in the convective stability criterion. It is a combination of → Ledoux’s criterion (or possibly → Schwarzschild’s criterion) and → Rayleigh’s criterion. Both the dynamical shear and Solberg-Høiland instabilities occur in the case of a very large → angular velocity decrease outwards.

Therefore, in a → rotating star the Ledoux or Schwarzschild criteria for convective instability should be replaced by the Solberg-Høiland criterion. More specifically, this criterion accounts for the difference of the centrifugal force for an adiabatically displaced fluid element.

It is also known as the axisymmetric baroclinic instability. It arises when the net force (gravity + buoyancy + centrifugal force) applied to a fluid parcel in an adiabatical displacement has components only in the direction of the displacement (A. Maeder, Physics, Formation and Evolution of Rotating Stars, 2009, Springer).

See also: E. Høiland, 1939, On the Interpretation and Application of the Circulation Theorems of V. Bjerknes. Archiv for mathematik og naturvidenskab. B. XLII. Nr. 5. Oslo.

H. Solberg, 1936 (reprint), Le mouvement d’inertie de l’atmosphere stable et son rôle dans la théorie des cyclones.

H. Solberg, 1941, On the Stability of the Circular Vortex. Avhandl. utg. av Det Norske Videnskaps-Akademi i Oslo. I. Mat-Naturv. Klasse. No. 11.

Wasiutynski, J. 1946, Astrophysica Norvegica, 4, 1.

The bottom or under surface of the → foot.

Etymology (EN): M.E., from O.Fr., from L. solea “sandal, bottom of a shoe,” from solum “base, bottom, ground,” of unknown origin.

Etymology (PE): From kaf, “the sole of the foot; the palm of the hand,” → floor; pâ, → foot.

The bottom or under surface of the → foot.

Etymology (EN): M.E., from O.Fr., from L. solea “sandal, bottom of a shoe,” from solum “base, bottom, ground,” of unknown origin.

Etymology (PE): From kaf, “the sole of the foot; the palm of the hand,” → floor; pâ, → foot.

An optical compensator which produces a constant phase change over the entire field, as opposed to the phase change produced by the → Babinet compensator, which occurs progressively across the field. The compensator consists of two wedges of the same wedge angle and a parallel plate. The optic axes of the two wedges has the same orientation. These form a variable thickness plate. One of the wedges is assembled to the fixed parallel plate. The optic axis of the parallel plate is at 90° to that of the wedges. The other wedge is attached to a micrometer and moves to produce a thickness difference between the fixed and variable thickness plates, thus producing a phase delay.

See also: Jean-Baptiste Soleil (1798-1849); → compensateur.

An optical compensator which produces a constant phase change over the entire field, as opposed to the phase change produced by the → Babinet compensator, which occurs progressively across the field. The compensator consists of two wedges of the same wedge angle and a parallel plate. The optic axes of the two wedges has the same orientation. These form a variable thickness plate. One of the wedges is assembled to the fixed parallel plate. The optic axis of the parallel plate is at 90° to that of the wedges. The other wedge is attached to a micrometer and moves to produce a thickness difference between the fixed and variable thickness plates, thus producing a phase delay.

See also: Jean-Baptiste Soleil (1798-1849); → compensateur.

A long coil of insulated copper wire containing a large number of close turns. The strength of magnetic field produced by a current carrying solenoid is directly proportional to the number of turns in the solenoid and to the strength of current in the solenoid. It also depends on the nature of “core material” used in making the solenoid. The use of → soft iron rod as core in a solenoid produces the strongest magnetism.

Etymology (EN): From Fr. solénoïde “pipe-shaped,” from Gk. solen “pipe, channel” + combining form of eidos “form, shape,” → -oid.

Etymology (PE): Sulvâr, from sul “pipe, gutter,” Lori sil, Sangesari sula, Šahmirzâdi solla, Tabari seltek, may be cognate with Gk. solen, as above, + -vâr, → -oid.

A long coil of insulated copper wire containing a large number of close turns. The strength of magnetic field produced by a current carrying solenoid is directly proportional to the number of turns in the solenoid and to the strength of current in the solenoid. It also depends on the nature of “core material” used in making the solenoid. The use of → soft iron rod as core in a solenoid produces the strongest magnetism.

Etymology (EN): From Fr. solénoïde “pipe-shaped,” from Gk. solen “pipe, channel” + combining form of eidos “form, shape,” → -oid.

Etymology (PE): Sulvâr, from sul “pipe, gutter,” Lori sil, Sangesari sula, Šahmirzâdi solla, Tabari seltek, may be cognate with Gk. solen, as above, + -vâr, → -oid.

1. A body or object having → three  → dimensions (length, breadth, and thickness). Of or pertaining to bodies or figures of three dimensions.
   

2. One of the four main → states of → matter, in which the substance molecules vibrate about fixed positions. Unlike a gas or liquid, a solid has a fixed shape, and unlike a gas, a solid has a fixed volume.
   

3. Without holes, free from cavities, not hollow.
   

4. Dense, thick, or heavy in nature or appearance.
   

5. Reliable; that can be depended upon.

Etymology (EN): M.E., from O.Fr. solide “firm, dense, compact,” from L. solidus “firm, whole, entire,” from PIE base *sol- “whole;” cf. Mod.Pers. har “every, all, each, any;” O.Pers. haruva- “whole, all together;” Av. hauruua- “whole, at all, undamaged;” Skt. sárva- “whole, all, every, undivided;” Gk. holos “whole, complete;” L. salvus “whole, safe, healthy,” sollus “whole, entire, unbroken.”

Etymology (PE): Dafzé, from dafzak “big, gross, thick, hard” (Dehxodâ), variant dabz “thick, coarse,” → concentrated; cf. Ossetic baezgin “thick, dense;” Shughni divask, Oroshori devaskak “calf of the leg;” Khotanese baysga- “thick, deep, many, large;” Sogd. δβânz “wide, coarse;” Av. bəzuuant- “thick, dense,” bazah- “thickness;” Proto-Ir. *(d)banz- “to be(come) thick, dense;” cf. Gk. pakhos “thickness, coarseness;” Latvian biezs “thick” (Cheung 2007).

1. A body or object having → three  → dimensions (length, breadth, and thickness). Of or pertaining to bodies or figures of three dimensions.
   

2. One of the four main → states of → matter, in which the substance molecules vibrate about fixed positions. Unlike a gas or liquid, a solid has a fixed shape, and unlike a gas, a solid has a fixed volume.
   

3. Without holes, free from cavities, not hollow.
   

4. Dense, thick, or heavy in nature or appearance.
   

5. Reliable; that can be depended upon.

Etymology (EN): M.E., from O.Fr. solide “firm, dense, compact,” from L. solidus “firm, whole, entire,” from PIE base *sol- “whole;” cf. Mod.Pers. har “every, all, each, any;” O.Pers. haruva- “whole, all together;” Av. hauruua- “whole, at all, undamaged;” Skt. sárva- “whole, all, every, undivided;” Gk. holos “whole, complete;” L. salvus “whole, safe, healthy,” sollus “whole, entire, unbroken.”

Etymology (PE): Dafzé, from dafzak “big, gross, thick, hard” (Dehxodâ), variant dabz “thick, coarse,” → concentrated; cf. Ossetic baezgin “thick, dense;” Shughni divask, Oroshori devaskak “calf of the leg;” Khotanese baysga- “thick, deep, many, large;” Sogd. δβânz “wide, coarse;” Av. bəzuuant- “thick, dense,” bazah- “thickness;” Proto-Ir. *(d)banz- “to be(come) thick, dense;” cf. Gk. pakhos “thickness, coarseness;” Latvian biezs “thick” (Cheung 2007).

The figure formed by three or more planes meeting at a common point or formed at the vertex of a cone. The solid angle completely surrounding a point is 4π steradian. → steradian.

Etymology (EN): → solid; → angle.

Etymology (PE): Zâviyé, → angle; fazâyi “of or relating to space,” → space; jâmed, → solid.

The figure formed by three or more planes meeting at a common point or formed at the vertex of a cone. The solid angle completely surrounding a point is 4π steradian. → steradian.

Etymology (EN): → solid; → angle.

Etymology (PE): Zâviyé, → angle; fazâyi “of or relating to space,” → space; jâmed, → solid.

In electronics, based on or consisting chiefly or exclusively of semiconducting materials, components, and related devices.

See also: → solid; → state.

In electronics, based on or consisting chiefly or exclusively of semiconducting materials, components, and related devices.

See also: → solid; → state.

The branch of condensed matter physics concerned with the study of rigid matter or solids in terms of their constituent particles (electrons and nuclei). The bulk of solid-state physics theory and research is focused on the electromagnetic, thermodynamic, and structural properties of crystalline solids.

See also: → solid state; → physics.

The branch of condensed matter physics concerned with the study of rigid matter or solids in terms of their constituent particles (electrons and nuclei). The bulk of solid-state physics theory and research is focused on the electromagnetic, thermodynamic, and structural properties of crystalline solids.

See also: → solid state; → physics.

1. To become or make solid, hard, or firm.

See also: → solid; → -fy.

1. To become or make solid, hard, or firm.

See also: → solid; → -fy.

1. To become or make solid, hard, or firm.

See also: → solid; → -fy.

1. To become or make solid, hard, or firm.

See also: → solid; → -fy.

The state, property, or quality of being solid. Solidness.

See also: → solid; → -ity.

The state, property, or quality of being solid. Solidness.

See also: → solid; → -ity.

In the → phase diagram of a → mixture at constant pressure, (such as an → alloy), the → curve that separates the → liquid+solid → phase from the all solid phase.
Above the solidus some or all of the mixture will be in a liquid state. See also → liquidus.

See also: From L. solidus, → solid.

In the → phase diagram of a → mixture at constant pressure, (such as an → alloy), the → curve that separates the → liquid+solid → phase from the all solid phase.
Above the solidus some or all of the mixture will be in a liquid state. See also → liquidus.

See also: From L. solidus, → solid.

Math., Physics: A solution of a certain type of partial differential equation that represents a solitary wave.
A soliton is a self-reinforcing wave that maintains its shape while it travels at constant speed. Solitons are caused by a cancellation of nonlinear and dispersive effects in the medium.

See also: From solit(ary) + → -on.

Math., Physics: A solution of a certain type of partial differential equation that represents a solitary wave.
A soliton is a self-reinforcing wave that maintains its shape while it travels at constant speed. Solitons are caused by a cancellation of nonlinear and dispersive effects in the medium.

See also: From solit(ary) + → -on.

Either of the two points on the → ecliptic at which the apparent → longitude of the → Sun is 90° or 270°. Also the time at which the Sun is at either point. Solstices occur when the Earth’s axis is oriented directly toward or away from the Sun, causing the Sun to reach its northernmost and southernmost extremes. → summer solstice, → winter solstice.

Etymology (EN): M.E., from O.Fr. solstice, from L. solstitium “point at which the sun seems to stand still,” from sol, → sun, cognate with Pers. xor, xoršid, hur, as below, + p.p. stem of sistere “to come to a stop, make stand still,” akin to Pers. istâdan “to stand,” as below.

Etymology (PE): Xoristân, is composed of two components. The first one xor “sun,” variant hur; Mid.Pers. xwar
“sun;” Av. hū-, hvar- “sun;” cf. Skt. surya-, Gk. helios, L. sol, cognate with E. sun, as above;
PIE base *sawel- “sun.” The second component istân “standing,” from istâdan “to stand;” Mid.Pers. êstâtan;
O.Pers./Av. sta- “to stand, stand still; set;” Av. hištaiti; cf. Skt. sthā- “to stand;” Gk. histemi “put, place, weigh,” stasis “a standing still;” L. stare “to stand;” Lith. statau “place;” Goth. standan; PIE base *sta- “to stand.”

Either of the two points on the → ecliptic at which the apparent → longitude of the → Sun is 90° or 270°. Also the time at which the Sun is at either point. Solstices occur when the Earth’s axis is oriented directly toward or away from the Sun, causing the Sun to reach its northernmost and southernmost extremes. → summer solstice, → winter solstice.

Etymology (EN): M.E., from O.Fr. solstice, from L. solstitium “point at which the sun seems to stand still,” from sol, → sun, cognate with Pers. xor, xoršid, hur, as below, + p.p. stem of sistere “to come to a stop, make stand still,” akin to Pers. istâdan “to stand,” as below.

Etymology (PE): Xoristân, is composed of two components. The first one xor “sun,” variant hur; Mid.Pers. xwar
“sun;” Av. hū-, hvar- “sun;” cf. Skt. surya-, Gk. helios, L. sol, cognate with E. sun, as above;
PIE base *sawel- “sun.” The second component istân “standing,” from istâdan “to stand;” Mid.Pers. êstâtan;
O.Pers./Av. sta- “to stand, stand still; set;” Av. hištaiti; cf. Skt. sthā- “to stand;” Gk. histemi “put, place, weigh,” stasis “a standing still;” L. stare “to stand;” Lith. statau “place;” Goth. standan; PIE base *sta- “to stand.”

The great circle of the celestial sphere which passes through the poles of the celestial equator and the solstice points. → equinoctial colure.

See also: Solsticial, adj. of → solstice; → colure.

The great circle of the celestial sphere which passes through the poles of the celestial equator and the solstice points. → equinoctial colure.

See also: Solsticial, adj. of → solstice; → colure.

The two points of the ecliptic the most distant from the equator.

See also: Solsticial, adj. of → solstice; → point.

The two points of the ecliptic the most distant from the equator.

See also: Solsticial, adj. of → solstice; → point.

Chem.: Capable of being dissolved .

Etymology (EN): M.E., from M.Fr. soluble, from L.L. solubilis “that may be loosened or dissolved,” from stem of L. solvere “loosen, dissolve,” → solve.

Etymology (PE): Luyidani, from luyidan, → solve + -i, → -able.

Chem.: Capable of being dissolved .

Etymology (EN): M.E., from M.Fr. soluble, from L.L. solubilis “that may be loosened or dissolved,” from stem of L. solvere “loosen, dissolve,” → solve.

Etymology (PE): Luyidani, from luyidan, → solve + -i, → -able.

Chem.: A substance which is dissolved in a solvent to form a solution.

Etymology (EN): From L. solutus, p.p. of solvere “to loosen, dissolve,” → solve.

Etymology (PE): Luyešt, from luyešte, p.p. of luyeštan, variant of luyidan, → solve.

Chem.: A substance which is dissolved in a solvent to form a solution.

Etymology (EN): From L. solutus, p.p. of solvere “to loosen, dissolve,” → solve.

Etymology (PE): Luyešt, from luyešte, p.p. of luyeštan, variant of luyidan, → solve.

1. The act of solving a problem, question. The state of being solved.
   

2a) Math.: The process of determining the answer to a problem. The answer itself.

2b) Math.: Of a differential equation, any function which, when put into the equation, converts it into an identity.

3. Chem.: The process by which a gas, liquid, or solid is dispersed homogeneously in a gas, liquid, or solid without chemical change. a homogeneous, molecular mixture of two or more substances.

See also: Verbal noun of → solve.

1. The act of solving a problem, question. The state of being solved.
   

2a) Math.: The process of determining the answer to a problem. The answer itself.

2b) Math.: Of a differential equation, any function which, when put into the equation, converts it into an identity.

3. Chem.: The process by which a gas, liquid, or solid is dispersed homogeneously in a gas, liquid, or solid without chemical change. a homogeneous, molecular mixture of two or more substances.

See also: Verbal noun of → solve.

Any of a class of chemical reactions in which solute and solvent molecules combine.

Etymology (EN): From solv(ent), → solvent + -ation.

Etymology (PE): Luyé, from luy- the stem of luyidé→ solute and luyandé→ solvent + -é nuance suffix.

Any of a class of chemical reactions in which solute and solvent molecules combine.

Etymology (EN): From solv(ent), → solvent + -ation.

Etymology (PE): Luyé, from luy- the stem of luyidé→ solute and luyandé→ solvent + -é nuance suffix.

1. To find an answer or solution to; clear up; explain. related concept: → dissolve.
   
2. To make a solution of, as by mixing with liquid.

Etymology (EN): M.E. solven, from L. solvere “to loosen, dissolve, untie,” from PIE *se-lu-, from reflexive pronoun *swe- + base *leu- “to loosen, divide, cut apart;” cf. Gk. lyein “to loosen, release, untie,” O.E. -leosan “to lose,” leas “loose;” E. lose, loose and Ger. los derive from this root.

Etymology (PE): Luyidan, infinitive from stem lu(y)-, from
lu, variant of Mod.Pers. las “loose,” lâ “slit, cut,” luš “torn,” lok “torn, piece,” lâc “open, wide open;” lu, lunoti “to cut, sever, mow, pluck, tear asunder, destroy,” lava “cutting, plucking; what is cut; fragment, piece;” Gk. lyein “to loosen, release, untie,” as above. PIE *leu- “to loosen, divide, cut apart”.

1. To find an answer or solution to; clear up; explain. related concept: → dissolve.
   
2. To make a solution of, as by mixing with liquid.

Etymology (EN): M.E. solven, from L. solvere “to loosen, dissolve, untie,” from PIE *se-lu-, from reflexive pronoun *swe- + base *leu- “to loosen, divide, cut apart;” cf. Gk. lyein “to loosen, release, untie,” O.E. -leosan “to lose,” leas “loose;” E. lose, loose and Ger. los derive from this root.

Etymology (PE): Luyidan, infinitive from stem lu(y)-, from
lu, variant of Mod.Pers. las “loose,” lâ “slit, cut,” luš “torn,” lok “torn, piece,” lâc “open, wide open;” lu, lunoti “to cut, sever, mow, pluck, tear asunder, destroy,” lava “cutting, plucking; what is cut; fragment, piece;” Gk. lyein “to loosen, release, untie,” as above. PIE *leu- “to loosen, divide, cut apart”.

Substance having the power of dissolving other substances in it.

See also: Agent noun of → solve.

Substance having the power of dissolving other substances in it.

See also: Agent noun of → solve.

A → spiral galaxy in the constellation → Virgo. It was the first galaxy whose rotation was detected. Also named M104 and NGC 4594.

Etymology (EN): Sp. sombrero “broad-brimmed hat,” originally “umbrella or parasol,”
from sombra “shade,” from L.L. subumbrare,
from → sub- “under” + umbra “shade, shadow;” → galaxy.

Etymology (PE): Kahkešân, → galaxy; sombrero, Sp., as above.

A → spiral galaxy in the constellation → Virgo. It was the first galaxy whose rotation was detected. Also named M104 and NGC 4594.

Etymology (EN): Sp. sombrero “broad-brimmed hat,” originally “umbrella or parasol,”
from sombra “shade,” from L.L. subumbrare,
from → sub- “under” + umbra “shade, shadow;” → galaxy.

Etymology (PE): Kahkešân, → galaxy; sombrero, Sp., as above.

A rocket or balloon carrying instruments to probe conditions in the upper atmosphere.

Etymology (EN): From Fr. sonde “ounding line; plumb line.”

Etymology (PE): Gomâné “a shaft sunk in order to ascertain the depth of the water when making a subterraneous canal,” from Proto-Iranian *vi-mā-, from vi- “apart, away from, out” (cf. Av. vi-; O.Pers. viy- “apart, away;” Skt. vi- “apart, asunder, away, out;” L. vitare “to avoid, turn aside”) + mā- “to measure” (cf.
O.Pers./Av. mā(y)- “to measure;” Mod.Pers.
mâ/mun/mân “measure,” as in Pers. terms âzmâ- “to test;”
pirâmun “perimeter,” âzmun “test, trial,”
peymân “measuring, agreement,” peymâné “a measure; a cup, bowl;”
PIE base *me- “to measure;”
cf. Skt. mati “measures,” matra- “measure;” Gk. metron “measure;” L. metrum).

A rocket or balloon carrying instruments to probe conditions in the upper atmosphere.

Etymology (EN): From Fr. sonde “ounding line; plumb line.”

Etymology (PE): Gomâné “a shaft sunk in order to ascertain the depth of the water when making a subterraneous canal,” from Proto-Iranian *vi-mā-, from vi- “apart, away from, out” (cf. Av. vi-; O.Pers. viy- “apart, away;” Skt. vi- “apart, asunder, away, out;” L. vitare “to avoid, turn aside”) + mā- “to measure” (cf.
O.Pers./Av. mā(y)- “to measure;” Mod.Pers.
mâ/mun/mân “measure,” as in Pers. terms âzmâ- “to test;”
pirâmun “perimeter,” âzmun “test, trial,”
peymân “measuring, agreement,” peymâné “a measure; a cup, bowl;”
PIE base *me- “to measure;”
cf. Skt. mati “measures,” matra- “measure;” Gk. metron “measure;” L. metrum).

Of, relating to, or being the speed of sound in a medium.

Etymology (EN): From L. sonus, → sound.

Etymology (PE): Sedâyi, pertaining to sedâ, → sound.

Of, relating to, or being the speed of sound in a medium.

Etymology (EN): From L. sonus, → sound.

Etymology (PE): Sedâyi, pertaining to sedâ, → sound.

A noise caused by a shock wave that emanates from an object traveling at or above the speed of sound.

Etymology (EN): → sonic; boom, M.E. bombon, bummyn “to buzz;” cf. Du. bommen, Ger. bummen, word made by sound imitation.

Etymology (PE): Qariv “shout, clamour, cry;” sedâyi, → sonic.

A noise caused by a shock wave that emanates from an object traveling at or above the speed of sound.

Etymology (EN): → sonic; boom, M.E. bombon, bummyn “to buzz;” cf. Du. bommen, Ger. bummen, word made by sound imitation.

Etymology (PE): Qariv “shout, clamour, cry;” sedâyi, → sonic.

The point where the → stellar wind makes a transition from → subsonic to → supersonic flow. In the particular case of a spherically symmetric wind (thus with no magnetic field), the distance from star, at which the sonic point occurs, is given by: r_s = (GM)/2c_s², where G is the → gravitational constant, M is the stellar mass, and c_s the → sound speed at the sonic point.

See also: → sonic; → point.

The point where the → stellar wind makes a transition from → subsonic to → supersonic flow. In the particular case of a spherically symmetric wind (thus with no magnetic field), the distance from star, at which the sonic point occurs, is given by: r_s = (GM)/2c_s², where G is the → gravitational constant, M is the stellar mass, and c_s the → sound speed at the sonic point.

See also: → sonic; → point.

To gather on a surface either by absorption, adsorption, or a combination of the two processes.

Etymology (EN): Verb, from sorption, extracted from → absorption→ adsorption, from L. sorbere “suck in,” from PIE base *srebh- “to suck, absorb” (cf. Arm. arbi “I drank;” Gk. rhopheo “to gulp down;” Lith. srebiu “to drink greedily”).

Etymology (PE): Šamidan, from šam, variant of šâm, as in âšâm, âšâmidan “to drink, to sip;” Av. šam- “to drink, sip, swallow;” Skt. cam, camati “to sip, dirink, lick up, absorb.”

To gather on a surface either by absorption, adsorption, or a combination of the two processes.

Etymology (EN): Verb, from sorption, extracted from → absorption→ adsorption, from L. sorbere “suck in,” from PIE base *srebh- “to suck, absorb” (cf. Arm. arbi “I drank;” Gk. rhopheo “to gulp down;” Lith. srebiu “to drink greedily”).

Etymology (PE): Šamidan, from šam, variant of šâm, as in âšâm, âšâmidan “to drink, to sip;” Av. šam- “to drink, sip, swallow;” Skt. cam, camati “to sip, dirink, lick up, absorb.”

The process of sorbing. The state of being sorbed. → absorption; → adsorption.

See also: Verbal noun of → sorb

The process of sorbing. The state of being sorbed. → absorption; → adsorption.

See also: Verbal noun of → sorb

The interval after which the heliacal rising of the star Sirius occurs at the same time of the year. It is a period of 1,460 Sothic years.

Etymology (EN): From Fr. sothique, from Gk. Sothis, an Egyptian name of Sirius; → period.

Etymology (PE): Tištari, of or pertaining to Tištar→ serius; dowré, → period.

The interval after which the heliacal rising of the star Sirius occurs at the same time of the year. It is a period of 1,460 Sothic years.

Etymology (EN): From Fr. sothique, from Gk. Sothis, an Egyptian name of Sirius; → period.

Etymology (PE): Tištari, of or pertaining to Tištar→ serius; dowré, → period.

The Egyptian year of 365 days and 6 hours, as distinguished from them Egyptian vague year, which contained 365 days.

Etymology (EN): From Fr. sothique, from Gk. Sothis, an Egyptian name of Sirius; → year.

Etymology (PE): Tištari, of or pertaining to Tištar→ serius; sâl, → year.

The Egyptian year of 365 days and 6 hours, as distinguished from them Egyptian vague year, which contained 365 days.

Etymology (EN): From Fr. sothique, from Gk. Sothis, an Egyptian name of Sirius; → year.

Etymology (PE): Tištari, of or pertaining to Tištar→ serius; sâl, → year.

1. A physiological sensation received by the ear. It is caused by a vibrating source and transmitted as a longitudinal pressure wave motion through a material medium such as air.
   

2a) Free from damage, injury, decay, etc.

2b) Describing an → argument→ iff its → reasoning is → valid and all its → premises are → true.

2c) Logic: A formal system is sound if all the → inferences
that are permitted by the rules of the system are valid inferences, that is, if no invalid arguments are provable within the system. → soundness.

Etymology (EN): 1) M.E. soun; O.Fr. son, from L. sonus “sound,” sonare “to sound;” PIE base *suen- “to sound;” cf. Av. x^van- “to sound;” Pers. x^vân-, x^vândan “to sing, read;”
Skt. svana- “sound,” svan- “to sound,” svanati “it sounds;” O.E. swinn “music, song”
(Cheung 2007).

2. M.E. sund, from O.E. gesund “sound, safe, having the organs and faculties complete and in perfect action,” cf. O.S. gisund, O.Fris. sund, Du. gezond, O.H.G. gisunt, Ger. gesund “healthy,” as in interjection gesundheit.

Etymology (PE): 1) Sedâ “sound,” most probably a Pers. term, since it exists also in Indo-Aryan
languages: Skt. (late Vedic): sabda “articulate sound, noise,”
Pali and Prakriti: sadda “sound, noise,” Sindhi: sadu, sado “shout, call,” Gujrâti sad “call, voice, echo,” Marathi: sad “shouting to,” Konkani sad “sound,”
Sinhali: sada “sound.” Therefore,
sadâ in Ar. “reverberating noise, echo” maybe a loan from Pers., or a coincidence. Note that for the author of the classical Pers. dictionary Borhân-e Qâte’ (India, 1652 A.D.), the Ar. term is a loanword from Pers.

2. Dorvâ (Dehxodâ) “whole, right, just;” Qâyeni, Gonâbâdi, Tabasi, Râvari dorvâx “healthy, whole,” dorvâxi “health” (related to Pers. dorud “benediction, praise,” dorost “whole, healthy, right”); cf. Sogd. žûk (from *druva-) “healthy;” O.Pers. duruwa- “healthy, firm, secure;” Av. druua- “healthy, firm, sound,” druuatāt “health, soundness,” drvô.cašman- “of sound eyes;” Skt. dhruvá- “fixed, firm;” → integral.

1. A physiological sensation received by the ear. It is caused by a vibrating source and transmitted as a longitudinal pressure wave motion through a material medium such as air.
   

2a) Free from damage, injury, decay, etc.

2b) Describing an → argument→ iff its → reasoning is → valid and all its → premises are → true.

2c) Logic: A formal system is sound if all the → inferences
that are permitted by the rules of the system are valid inferences, that is, if no invalid arguments are provable within the system. → soundness.

Etymology (EN): 1) M.E. soun; O.Fr. son, from L. sonus “sound,” sonare “to sound;” PIE base *suen- “to sound;” cf. Av. x^van- “to sound;” Pers. x^vân-, x^vândan “to sing, read;”
Skt. svana- “sound,” svan- “to sound,” svanati “it sounds;” O.E. swinn “music, song”
(Cheung 2007).

2. M.E. sund, from O.E. gesund “sound, safe, having the organs and faculties complete and in perfect action,” cf. O.S. gisund, O.Fris. sund, Du. gezond, O.H.G. gisunt, Ger. gesund “healthy,” as in interjection gesundheit.

Etymology (PE): 1) Sedâ “sound,” most probably a Pers. term, since it exists also in Indo-Aryan
languages: Skt. (late Vedic): sabda “articulate sound, noise,”
Pali and Prakriti: sadda “sound, noise,” Sindhi: sadu, sado “shout, call,” Gujrâti sad “call, voice, echo,” Marathi: sad “shouting to,” Konkani sad “sound,”
Sinhali: sada “sound.” Therefore,
sadâ in Ar. “reverberating noise, echo” maybe a loan from Pers., or a coincidence. Note that for the author of the classical Pers. dictionary Borhân-e Qâte’ (India, 1652 A.D.), the Ar. term is a loanword from Pers.

2. Dorvâ (Dehxodâ) “whole, right, just;” Qâyeni, Gonâbâdi, Tabasi, Râvari dorvâx “healthy, whole,” dorvâxi “health” (related to Pers. dorud “benediction, praise,” dorost “whole, healthy, right”); cf. Sogd. žûk (from *druva-) “healthy;” O.Pers. duruwa- “healthy, firm, secure;” Av. druua- “healthy, firm, sound,” druuatāt “health, soundness,” drvô.cašman- “of sound eyes;” Skt. dhruvá- “fixed, firm;” → integral.

A sharp increase in aerodynamic drag that occurs as the speed of an aircraft approaches the speed of sound. Also called sonic barrier.

See also: → sound; → barrier.

A sharp increase in aerodynamic drag that occurs as the speed of an aircraft approaches the speed of sound. Also called sonic barrier.

See also: → sound; → barrier.

The energy which → sound waves impart to a medium. Same as acoustic energy.

See also: → sound; → energy.

The energy which → sound waves impart to a medium. Same as acoustic energy.

See also: → sound; → energy.

The distribution of → sound energy in a defined space.

See also: → sound; → field.

The distribution of → sound energy in a defined space.

See also: → sound; → field.

The maximum distance a → sound wave could have traveled through the ionized plasma from the → Big Bang until the → recombination era. It is 150 → Mpc, or bout 500 million → light-years. Sound horizon is the equivalent of the concept of → cosmic horizon, where one replaces → electromagnetic wave by
→ sound wave. The sound horizon is a fixed physical scale at the → last scattering surface. Cosmological models relate the value of sound horizon to the angle it subtends on the sky today. Same as acoustic horizon and sonic horizon. See also → CMB angular power spectrum.

See also: → sound; → horizon.

The maximum distance a → sound wave could have traveled through the ionized plasma from the → Big Bang until the → recombination era. It is 150 → Mpc, or bout 500 million → light-years. Sound horizon is the equivalent of the concept of → cosmic horizon, where one replaces → electromagnetic wave by
→ sound wave. The sound horizon is a fixed physical scale at the → last scattering surface. Cosmological models relate the value of sound horizon to the angle it subtends on the sky today. Same as acoustic horizon and sonic horizon. See also → CMB angular power spectrum.

See also: → sound; → horizon.

The average → sound power passing through a unit area perpendicular to the direction that the sound is traveling. It is usually expressed in watts per square meter.

See also: → sound; → level.

The average → sound power passing through a unit area perpendicular to the direction that the sound is traveling. It is usually expressed in watts per square meter.

See also: → sound; → level.

The expression of sound intensity in decibel units. The sound intensity level
(L_I), in decibels, is computed as: L_I = 10 log (I/I₀), where I is the measured sound intensity and I₀ is the reference intensity (1 x 10 ^-12 watt per square meter).

See also: → sound; → intensity; → level.

The expression of sound intensity in decibel units. The sound intensity level
(L_I), in decibels, is computed as: L_I = 10 log (I/I₀), where I is the measured sound intensity and I₀ is the reference intensity (1 x 10 ^-12 watt per square meter).

See also: → sound; → intensity; → level.

The → sound energy emitted by a source per unit time, usually expressed in → watts. Sound power causes → sound pressure.

See also: → sound; → power.

The → sound energy emitted by a source per unit time, usually expressed in → watts. Sound power causes → sound pressure.

See also: → sound; → power.

The sound energy emitted by a sound source per unit time and expressed in → decibels. Sound power, in → watts, is converted to sound power level in decibels (L), by L = 10 log (W/W₀), where W₀ is the reference power (1 x 10 ^-12 watt).

See also: → sound; → power; → level.

The sound energy emitted by a sound source per unit time and expressed in → decibels. Sound power, in → watts, is converted to sound power level in decibels (L), by L = 10 log (W/W₀), where W₀ is the reference power (1 x 10 ^-12 watt).

See also: → sound; → power; → level.

The periodic fluctuation above and below atmospheric pressure created by an oscillating body which provides the → sound power. Instantaneous sound pressure is the peak value of air pressure.

See also: → sound; → pressure.

The periodic fluctuation above and below atmospheric pressure created by an oscillating body which provides the → sound power. Instantaneous sound pressure is the peak value of air pressure.

See also: → sound; → pressure.

The number of → overtones present in a sound and their respective intensity. Like → loudness, it is a subjective quantity and cannot be
measured with instruments.

See also: → sound; → quality.

The number of → overtones present in a sound and their respective intensity. Like → loudness, it is a subjective quantity and cannot be
measured with instruments.

See also: → sound; → quality.

The velocity of propagation of a → longitudinal wave in a medium under specified conditions. Also known as sonic speed, sonic velocity, acoustic velocity, sound velocity, velocity of sound, speed of sound. The speed of sound is a thermodynamic property that relates to the change in pressure and density of the medium and can be expressed as C = (dP/dρ)^1/2, where C is the sound velocity, dP is the change in pressure, and dρ the change in density. It can also be expressed as C = (E/ρ)^1/2, where E is the bulk modulus elasticity. This equation is valid for liquids, solids and gases. The sound travels faster through media with higher → elasticity and/or lower density. If a medium is → incompressible the speed of sound is infinite. For → ideal gases, a simple relationship exists between the sound speed and temperature: C = (γR T)^1/2, where γ is the → specific heat ratio (C_P/C_V), and R is the → gas constant. We see that for ideal gases it the speed is independent of pressure. In air at 0°C it is 332 m/sec. The speed of sound in a gas of hydrogen is 1315 m/s. → Mach number.

See also: → sound; → speed.

The velocity of propagation of a → longitudinal wave in a medium under specified conditions. Also known as sonic speed, sonic velocity, acoustic velocity, sound velocity, velocity of sound, speed of sound. The speed of sound is a thermodynamic property that relates to the change in pressure and density of the medium and can be expressed as C = (dP/dρ)^1/2, where C is the sound velocity, dP is the change in pressure, and dρ the change in density. It can also be expressed as C = (E/ρ)^1/2, where E is the bulk modulus elasticity. This equation is valid for liquids, solids and gases. The sound travels faster through media with higher → elasticity and/or lower density. If a medium is → incompressible the speed of sound is infinite. For → ideal gases, a simple relationship exists between the sound speed and temperature: C = (γR T)^1/2, where γ is the → specific heat ratio (C_P/C_V), and R is the → gas constant. We see that for ideal gases it the speed is independent of pressure. In air at 0°C it is 332 m/sec. The speed of sound in a gas of hydrogen is 1315 m/s. → Mach number.

See also: → sound; → speed.

A → longitudinal wave which when striking the ear gives rise to the sensation of sound. Such waves can be propagated in solids, liquids, and gases. The material particles transmitting sound waves oscillate in the direction of propagation of the wave itself. There is a large range of frequencies within which longitudinal waves can stimulate the human ear and brain to the sensation of hearing. This range is from about 20 → Hz to about 20,000 Hz and is called the audible range. → ultrasound; → infrasound.

See also: → sound; → wave.

A → longitudinal wave which when striking the ear gives rise to the sensation of sound. Such waves can be propagated in solids, liquids, and gases. The material particles transmitting sound waves oscillate in the direction of propagation of the wave itself. There is a large range of frequencies within which longitudinal waves can stimulate the human ear and brain to the sensation of hearing. This range is from about 20 → Hz to about 20,000 Hz and is called the audible range. → ultrasound; → infrasound.

See also: → sound; → wave.

1. In geophysics, any penetration of the natural environment for scientific observation.
   
2. In meteorology, a free, unmanned balloon carrying instruments aloft to make atmospheric measurements, esp. a radiosonde balloon.
   
3. The measurement of the depth of water beneath a vessel.

Etymology (EN): From Fr. sonder, → sonde.

Etymology (PE): From gomâné, → sonde, + zani verbal noun of zadan “to do; to strike, beat; to play an instrument” (Mid.Pers. zatan, žatan; O.Pers./Av. jan-, gan- “to strike, hit, smite, kill” (jantar- “smiter”); cf.
Skt. han- “to strike, beat” (hantar- “smiter, killer”);
Gk. theinein “to strike;” L. fendere “to strike, push;” Gmc. *gundjo “war, battle;” PIE *g^when- “to strike, kill”).

1. In geophysics, any penetration of the natural environment for scientific observation.
   
2. In meteorology, a free, unmanned balloon carrying instruments aloft to make atmospheric measurements, esp. a radiosonde balloon.
   
3. The measurement of the depth of water beneath a vessel.

Etymology (EN): From Fr. sonder, → sonde.

Etymology (PE): From gomâné, → sonde, + zani verbal noun of zadan “to do; to strike, beat; to play an instrument” (Mid.Pers. zatan, žatan; O.Pers./Av. jan-, gan- “to strike, hit, smite, kill” (jantar- “smiter”); cf.
Skt. han- “to strike, beat” (hantar- “smiter, killer”);
Gk. theinein “to strike;” L. fendere “to strike, push;” Gmc. *gundjo “war, battle;” PIE *g^when- “to strike, kill”).

A small, free balloon sent into the upper atmosphere to measure, record, and transmit meteorological reports to a ground station.

See also: → sounding; → balloon.

A small, free balloon sent into the upper atmosphere to measure, record, and transmit meteorological reports to a ground station.

See also: → sounding; → balloon.

1. The quality of being → sound.
   

2. Logic: The quality or condition of a → deductive reasoning if it meets the two conditions of
   → valid arguments and → true→ premises. These are the
   → necessary and sufficient conditions for soundness.

See also: → sound; → -ness.

1. The quality of being → sound.
   

2. Logic: The quality or condition of a → deductive reasoning if it meets the two conditions of
   → valid arguments and → true→ premises. These are the
   → necessary and sufficient conditions for soundness.

See also: → sound; → -ness.

General: Any thing or place from which something comes, arises, or is obtained.
Physics: A point, line, or area in space from which the lines of force in a vector field originate.
Electricity: Any active component, battery, or generator that supplies energy.
Thermodynamics: Any body, device, or system that provides energy.

Etymology (EN): M.E., from O.Fr. sourse “a rising, beginning, fountainhead of a river or stream,” from p.p. of sourdre “to rise, spring up,” from L. surgere “to rise,” → surge.

Etymology (PE): Xan “source,” variant xân (Gilaki xoni, Tabari xoni,Laki kyani, Tâleši xâni, xoni,); Mid.Pers. xân, xânig “source, spring,” Av. xâ-, xan- “source, fountain, spring,” xayana- “belonging to a spring;” cf. Khotanese khâhâ- “spring, fountain;” Skt. khâ’- “spring, source.”

General: Any thing or place from which something comes, arises, or is obtained.
Physics: A point, line, or area in space from which the lines of force in a vector field originate.
Electricity: Any active component, battery, or generator that supplies energy.
Thermodynamics: Any body, device, or system that provides energy.

Etymology (EN): M.E., from O.Fr. sourse “a rising, beginning, fountainhead of a river or stream,” from p.p. of sourdre “to rise, spring up,” from L. surgere “to rise,” → surge.

Etymology (PE): Xan “source,” variant xân (Gilaki xoni, Tabari xoni,Laki kyani, Tâleši xâni, xoni,); Mid.Pers. xân, xânig “source, spring,” Av. xâ-, xan- “source, fountain, spring,” xayana- “belonging to a spring;” cf. Khotanese khâhâ- “spring, fountain;” Skt. khâ’- “spring, source.”

For a radiating material, the ratio of emissivity to opacity.

See also: → source; → function.

For a radiating material, the ratio of emissivity to opacity.

See also: → source; → function.

The cardinal point which is opposite to north. It is also the direction of the Sun at local noon (in the northern hemisphere).

Etymology (EN): M.E. suth(e), south(e), from
O.E. suth “southward, in the south;” cf. O.S., O.Fris. suth “southward, in the south,” M.Du. suut), O.H.G. sund, perhaps related to base of *sunnon “sun,” with sense of “the region of the sun.”

Etymology (PE): Note: South is related to right since it is to the right when one faces the rising Sun.
This occurs in, for example, in Av., Skt., and O.Ir., as below.

Daštar, from Mid.Pers. dašn “right hand;” Av. dašina- “right;” Ossetic dæsni “skillful, dexterous;” cf. Skt. dáksina- “right; southern;” Gk. dexios («i>*deks-i-uo-) “right,” dexiteros “located on the right side;” L. dexter “right;” Goth. taihswo “right hand;” O.Ir. dess “on the right hand, southern;”

PIE base *deks- “right.” The second element -tar direction suffix, as in Mid.Pers. ošastar “east” (Av. ušastara- “eastern”), dôšastar “west” (Av. daôšatara-, daôšastara- “western”), abâxtar “north” (Av. apāxtara- “northern”), Mod.Pers. bâxtar, → west.

The cardinal point which is opposite to north. It is also the direction of the Sun at local noon (in the northern hemisphere).

Etymology (EN): M.E. suth(e), south(e), from
O.E. suth “southward, in the south;” cf. O.S., O.Fris. suth “southward, in the south,” M.Du. suut), O.H.G. sund, perhaps related to base of *sunnon “sun,” with sense of “the region of the sun.”

Etymology (PE): Note: South is related to right since it is to the right when one faces the rising Sun.
This occurs in, for example, in Av., Skt., and O.Ir., as below.

Daštar, from Mid.Pers. dašn “right hand;” Av. dašina- “right;” Ossetic dæsni “skillful, dexterous;” cf. Skt. dáksina- “right; southern;” Gk. dexios («i>*deks-i-uo-) “right,” dexiteros “located on the right side;” L. dexter “right;” Goth. taihswo “right hand;” O.Ir. dess “on the right hand, southern;”

PIE base *deks- “right.” The second element -tar direction suffix, as in Mid.Pers. ošastar “east” (Av. ušastara- “eastern”), dôšastar “west” (Av. daôšatara-, daôšastara- “western”), abâxtar “north” (Av. apāxtara- “northern”), Mod.Pers. bâxtar, → west.

A region of the Earth where the inner → Van Allen belt comes closest to the Earth’s surface. It is due to the fact that the → geomagnetic field is offset from the center of the Earth. The region is centered near 25 degrees South 50 degrees West, close to the Atlantic coast of Brazil. The excess of trapped energetic particles in that region presents a problem for satellites in orbit around the Earth.

See also: → south; → Atlantic; → anomaly.

A region of the Earth where the inner → Van Allen belt comes closest to the Earth’s surface. It is due to the fact that the → geomagnetic field is offset from the center of the Earth. The region is centered near 25 degrees South 50 degrees West, close to the Atlantic coast of Brazil. The excess of trapped energetic particles in that region presents a problem for satellites in orbit around the Earth.

See also: → south; → Atlantic; → anomaly.

The point in the → southern hemisphere where the → rotation axis of the Earth touches the → celestial sphere. In contrast to the → north celestial pole, no bright star is visible in that direction.

See also: → north; → celestial; → pole.

The point in the → southern hemisphere where the → rotation axis of the Earth touches the → celestial sphere. In contrast to the → north celestial pole, no bright star is visible in that direction.

See also: → north; → celestial; → pole.

The point on → horizon in direction of → geographic south pole.

See also: → south; → point.

The point on → horizon in direction of → geographic south pole.

See also: → south; → point.

A large area of the south polar region of → Mars which is covered with layers of → water ice and → dust.

The SPLD, like the NPLD, has a maximum relief relative to the surrounding terrain of ~ 3.5 km and ~ 1,000 km across.

Above the SPLD lies a very thin temporary (1-10 m) cap of → carbon dioxide ice/frost that snows out in the winter and sublimates over the spring and summer seasons.

It is believed that the rhythmic nature of the deposits is related to oscillations in Mars’ → orbital parameters (J. J. Plaut et al., 2007, Science 316, 92).

See also: → south; → polar; → layer; → deposit.

A large area of the south polar region of → Mars which is covered with layers of → water ice and → dust.

The SPLD, like the NPLD, has a maximum relief relative to the surrounding terrain of ~ 3.5 km and ~ 1,000 km across.

Above the SPLD lies a very thin temporary (1-10 m) cap of → carbon dioxide ice/frost that snows out in the winter and sublimates over the spring and summer seasons.

It is believed that the rhythmic nature of the deposits is related to oscillations in Mars’ → orbital parameters (J. J. Plaut et al., 2007, Science 316, 92).

See also: → south; → polar; → layer; → deposit.

1. An → imaginary point in the → southern hemisphere representing the intersection of the → Earth’s → rotation axis with the → globe with the → celestial sphere.
   

2. For a → magnet, the pole which points toward the geographic south.
   

3. In a → magnetic field, the point which receives a → line of force coming from the
   → north pole.

See also: → south; → pole.

1. An → imaginary point in the → southern hemisphere representing the intersection of the → Earth’s → rotation axis with the → globe with the → celestial sphere.
   

2. For a → magnet, the pole which points toward the geographic south.
   

3. In a → magnetic field, the point which receives a → line of force coming from the
   → north pole.

See also: → south; → pole.

A star that would mark the south → celestial pole. Presently no bright visible star is situated along the → rotation axis of the Earth in the southern hemisphere. But, because of the Earth’s → axial precession, about 7,000 years from now the star → Delta Velorum in the constellation → Vela, the Sail, will come to within 0.2 degrees of the South Celestial Pole (around the year 9250 B.C.). That is closer to marking the celestial pole than → Polaris or → Sirius ever do during their reigns as pole stars!

 Sirius will become the South Pole Star some 60 thousand
 years from now (around the year 66270 B.C.). In that time, Sirius will
 come to within 1.6 degrees of the South Celestial Pole.

See also: → south; → celestial; → pole.

A star that would mark the south → celestial pole. Presently no bright visible star is situated along the → rotation axis of the Earth in the southern hemisphere. But, because of the Earth’s → axial precession, about 7,000 years from now the star → Delta Velorum in the constellation → Vela, the Sail, will come to within 0.2 degrees of the South Celestial Pole (around the year 9250 B.C.). That is closer to marking the celestial pole than → Polaris or → Sirius ever do during their reigns as pole stars!

 Sirius will become the South Pole Star some 60 thousand
 years from now (around the year 66270 B.C.). In that time, Sirius will
 come to within 1.6 degrees of the South Celestial Pole.

See also: → south; → celestial; → pole.

Of or pertaining to the south.

Etymology (EN): M.E., O.E. suðerne, from suð, → south,

• -erne, suffix denoting direction.

Etymology (PE): Daštari, relating to daštar, → south.

Of or pertaining to the south.

Etymology (EN): M.E., O.E. suðerne, from suð, → south,

• -erne, suffix denoting direction.

Etymology (PE): Daštari, relating to daštar, → south.

Popular name for the constellation → Crux. Its four brightest stars form a distinctive cross shape.

See also: → southern; → Crux.

Popular name for the constellation → Crux. Its four brightest stars form a distinctive cross shape.

See also: → southern; → Crux.

The half of the → Earth or another → north pole between the → south pole and the → equator.

See also: → southern; → hemisphere.

The half of the → Earth or another → north pole between the → south pole and the → equator.

See also: → southern; → hemisphere.

The transit of a celestial object, especially the Sun, across the meridian due south of the observer.

Etymology (EN): Verbal noun from → south (v.).

Etymology (PE): Gozar-e daštar-su, literally “passage southward,” from gozar, → passage; daštar→ south; su, → direction.

The transit of a celestial object, especially the Sun, across the meridian due south of the observer.

Etymology (EN): Verbal noun from → south (v.).

Etymology (PE): Gozar-e daštar-su, literally “passage southward,” from gozar, → passage; daštar→ south; su, → direction.