An Etymological Dictionary of Astronomy and Astrophysics

A prefix meaning “good, well; true, genuine” (eupepsia; eukaryote); opposed to → dys-.

Etymology (EN): L. from Gk. eu “well,” combining form of eus “good” (hu-gies “healthy”); cf. Mid.Pers. hu-; Av. hu- “good;” PIE base *su- “good,” see below.

Etymology (PE): Mid.Pers. hu- “good, well” (hu-boy “sweet-smelling,” hu-cihr “beautiful,” hu-mânih “good-mindedness”); O.Pers. ^hu- “good, well” (ukāra- “having good people”); Av. hu-, hū- “well, good, beautiful” (hu-kərp- “well-shapen,” hūxta- “well spoken,” hu-manah- “good-minded”); Skt. su- “good” (svasti “well-being, good luck,” sumánas- “good-minded,” sūktá- “well spoken”); Gallic su-; O.S. su-; Welsh hy-; PIE base *su-, as above.

A prefix meaning “good, well; true, genuine” (eupepsia; eukaryote); opposed to → dys-.

Etymology (EN): L. from Gk. eu “well,” combining form of eus “good” (hu-gies “healthy”); cf. Mid.Pers. hu-; Av. hu- “good;” PIE base *su- “good,” see below.

Etymology (PE): Mid.Pers. hu- “good, well” (hu-boy “sweet-smelling,” hu-cihr “beautiful,” hu-mânih “good-mindedness”); O.Pers. ^hu- “good, well” (ukāra- “having good people”); Av. hu-, hū- “well, good, beautiful” (hu-kərp- “well-shapen,” hūxta- “well spoken,” hu-manah- “good-minded”); Skt. su- “good” (svasti “well-being, good luck,” sumánas- “good-minded,” sūktá- “well spoken”); Gallic su-; O.S. su-; Welsh hy-; PIE base *su-, as above.

Of or pertaining to Euclid, or his postulates. → Euclidean division, → Euclidean geometry, → Euclidean space, → non-Euclidean geometry.

See also: After the Gk. geometrician and educator at Alexandria, around 300 B.C., who applied the deductive principles of logic to geometry, thereby deriving statements from clearly defined axioms.

Of or pertaining to Euclid, or his postulates. → Euclidean division, → Euclidean geometry, → Euclidean space, → non-Euclidean geometry.

See also: After the Gk. geometrician and educator at Alexandria, around 300 B.C., who applied the deductive principles of logic to geometry, thereby deriving statements from clearly defined axioms.

In arithmetic, the conventional process of division of two → integers. For a → real number a divided by b > 0, there exists a unique integer q and a real number r, 0 ≤ r «i>b, such that a = qb + r.

See also: → Euclidean; → division.

In arithmetic, the conventional process of division of two → integers. For a → real number a divided by b > 0, there exists a unique integer q and a real number r, 0 ≤ r «i>b, such that a = qb + r.

See also: → Euclidean; → division.

The geometry based on the postulates or descriptions of Euclid. One of the critical assumptions of the Euclidean geometry is given in his fifth postulate: through a point not on a line, one and only one line be drawn parallel to the given line. See also → non-Euclidean geometry.

See also: → Euclidean; → geometry.

The geometry based on the postulates or descriptions of Euclid. One of the critical assumptions of the Euclidean geometry is given in his fifth postulate: through a point not on a line, one and only one line be drawn parallel to the given line. See also → non-Euclidean geometry.

See also: → Euclidean; → geometry.

A space in which the → distance between any two points is given by the → Pythagorean theorem: d² = (Δx)² + (Δy)² + (Δz)², where d is distance and Δx, Δy, and Δz are differential → Cartesian coordinates. Euclidean n-space Rⁿ is the set of all column vectors with n real entries.

See also: → Euclidean; → space.

A space in which the → distance between any two points is given by the → Pythagorean theorem: d² = (Δx)² + (Δy)² + (Δz)², where d is distance and Δx, Δy, and Δz are differential → Cartesian coordinates. Euclidean n-space Rⁿ is the set of all column vectors with n real entries.

See also: → Euclidean; → space.

→ spheres of Eudoxus.

See also: → spheres of Eudoxus.

→ spheres of Eudoxus.

See also: → spheres of Eudoxus.

Leonhard Euler (1707-1783), the eminent Swiss mathematician, physicist, and astronomer.

Leonhard Euler (1707-1783), the eminent Swiss mathematician, physicist, and astronomer.

In → fluid mechanics, one of a set of → differential equations that govern the motion of a → compressible, → inviscid fluid. Euler equations correspond to the → Navier-Stokes equations with zero
→ viscosity.

See also: → Euler; → equation.

In → fluid mechanics, one of a set of → differential equations that govern the motion of a → compressible, → inviscid fluid. Euler equations correspond to the → Navier-Stokes equations with zero
→ viscosity.

See also: → Euler; → equation.

In any → triangle, the straight line on which always lie the → centroid, → circumcenter, and → orthocenter.

See also: → Euler; → line.

In any → triangle, the straight line on which always lie the → centroid, → circumcenter, and → orthocenter.

See also: → Euler; → line.

The line drawn in a coordinate plane connecting the approximate values of the solution of a → first-order differential equation.

See also: → Euler; → broken line.

The line drawn in a coordinate plane connecting the approximate values of the solution of a → first-order differential equation.

See also: → Euler; → broken line.

A formula which expresses an → exponential function with an → imaginary number  → exponent in terms of → trigonometric functions:
e^iθ = cos θ + i sinθ,
e^-iθ = cos θ - i sinθ,
cosθ = (e^iθ + e^-iθ)/2,
sinθ = (e^iθ - e^-iθ)/2i.

In the particular case of θ = π, Euler’s formula becomes: e^iπ + 1 = 0, which is considered by many mathematicians to be the most elegant mathematical equation. → mathematical elegance.

See also: → Euler; → formula.

A formula which expresses an → exponential function with an → imaginary number  → exponent in terms of → trigonometric functions:
e^iθ = cos θ + i sinθ,
e^-iθ = cos θ - i sinθ,
cosθ = (e^iθ + e^-iθ)/2,
sinθ = (e^iθ - e^-iθ)/2i.

In the particular case of θ = π, Euler’s formula becomes: e^iπ + 1 = 0, which is considered by many mathematicians to be the most elegant mathematical equation. → mathematical elegance.

See also: → Euler; → formula.

Fluid mechanics: A method in which the changes in the physical properties
of the fluid, such as velocity, acceleration, and density are described at a fixed point in space occupied by the fluid. Compare with → Lagrangian method.

See also: → Euler; → method.

Fluid mechanics: A method in which the changes in the physical properties
of the fluid, such as velocity, acceleration, and density are described at a fixed point in space occupied by the fluid. Compare with → Lagrangian method.

See also: → Euler; → method.

An inoffensive word or phrase substituted for one considered offensive or hurtful, especially one concerned with religion, sex, death, or excreta (TheFreeDictionary.com).

Etymology (EN): From Gk. euphemismos, from euphemizein “speak with fair words, use words of good omen,” from → eu- “well,” + pheme “speech, voice, talk,” from phanai “to speak,” ultimately from PIE *bha-
“to speak, tell, say;” cf. Skt. bhanati “speaks;” L. fari “to say,” fabula “tale, story,” fama “talk, rumor, report; reputation;” Armenian ban, bay “word, term.”

Etymology (PE): Xošguyi, xošzabâni, literally “pleasant talking, ~ speach,” from xoš “well, pleasant,” → eu- + guyi verbal noun of goftan “to say, talk, speak,” → logic; zabâni, from zabân, → language.

An inoffensive word or phrase substituted for one considered offensive or hurtful, especially one concerned with religion, sex, death, or excreta (TheFreeDictionary.com).

Etymology (EN): From Gk. euphemismos, from euphemizein “speak with fair words, use words of good omen,” from → eu- “well,” + pheme “speech, voice, talk,” from phanai “to speak,” ultimately from PIE *bha-
“to speak, tell, say;” cf. Skt. bhanati “speaks;” L. fari “to say,” fabula “tale, story,” fama “talk, rumor, report; reputation;” Armenian ban, bay “word, term.”

Etymology (PE): Xošguyi, xošzabâni, literally “pleasant talking, ~ speach,” from xoš “well, pleasant,” → eu- + guyi verbal noun of goftan “to say, talk, speak,” → logic; zabâni, from zabân, → language.

The → continents of → Europe and → Asia considered as a whole.

See also: From Euro-, → Europe, + → Asia.

The → continents of → Europe and → Asia considered as a whole.

See also: From Euro-, → Europe, + → Asia.

The sixth of → Jupiter’s known moons
and the fourth largest; it is the second of the → Galilean satellites. With a diameter of 3140 km, Europa is slightly smaller than Earth’s Moon. Its mass is 4.80 × 10²² kg, i.e.
1.5 times less massive than Earth Moon. Its distance to Jupiter is 670,900 km, or about 9 Jovian radii. Its → orbital period is 3.55 Earth days which
equals its → rotation period.
Europa’s density is 3.0 g cm^-3, typical of a mixture of rocks including → ice. Its high → albedo (0.67) suggests that its surface is mostly → water ice. The → surface temperature of Europa ranges between about 125 K (-150 °C) at the equator and about 50 K (-220 °C) at the poles. There are few → impact craters on Europa, because its surface is too active and therefore young. The most striking features of Europa’s surface are structures called → lineae and → lenticulae. The thickness of the ice crust could range between a few kilometers to a few tens of kilometers. It is now believed that there is an ocean of salty water, up to 100 km deep, flowing under Europa’s ice. Europa’s ocean is kept liquid due to → tidal heating by Jupiter.

See also: In Gk. mythology, Europa was a Phoenician princess (Agenor’s daughter) abducted to Crete by Zeus, who had assumed the form of a white bull, and by him the mother of Minos, Sarpedon, and Rhadamanthys.

The sixth of → Jupiter’s known moons
and the fourth largest; it is the second of the → Galilean satellites. With a diameter of 3140 km, Europa is slightly smaller than Earth’s Moon. Its mass is 4.80 × 10²² kg, i.e.
1.5 times less massive than Earth Moon. Its distance to Jupiter is 670,900 km, or about 9 Jovian radii. Its → orbital period is 3.55 Earth days which
equals its → rotation period.
Europa’s density is 3.0 g cm^-3, typical of a mixture of rocks including → ice. Its high → albedo (0.67) suggests that its surface is mostly → water ice. The → surface temperature of Europa ranges between about 125 K (-150 °C) at the equator and about 50 K (-220 °C) at the poles. There are few → impact craters on Europa, because its surface is too active and therefore young. The most striking features of Europa’s surface are structures called → lineae and → lenticulae. The thickness of the ice crust could range between a few kilometers to a few tens of kilometers. It is now believed that there is an ocean of salty water, up to 100 km deep, flowing under Europa’s ice. Europa’s ocean is kept liquid due to → tidal heating by Jupiter.

See also: In Gk. mythology, Europa was a Phoenician princess (Agenor’s daughter) abducted to Crete by Zeus, who had assumed the form of a white bull, and by him the mother of Minos, Sarpedon, and Rhadamanthys.

The northern hemisphere → continent that has the Atlantic Ocean to its west, the Arctic Ocean to its north, Asia to its east, and Africa to its south (area 10,354,636 square kilometers).

See also: From → Europa.

The northern hemisphere → continent that has the Atlantic Ocean to its west, the Arctic Ocean to its north, Asia to its east, and Africa to its south (area 10,354,636 square kilometers).

See also: From → Europa.

Of or relating to Europe or its inhabitants.

See also: → Europe.

Of or relating to Europe or its inhabitants.

See also: → Europe.

An major intergovernmental research organisation in astronomy supported by 14 European countries. ESO was founded in 1962 as a consortium among Belgium, Denmark, France, Germany, the Netherlands, and Sweden. The ESO Headquarters are located in Garching near Munich, Germany. The organization operates three outstanding observing sites in the Atacama Desert region of Chile: → La Silla, → Paranal, and Chajnantor. The → Very Large Telescope (VLT), the world’s most advanced visible-light astronomical facility, is located on the 2600 m high mountain of Paranal, which also hosts the → VLT Interferometer (VLTI). The Chajnantor site, 5000 m above sea level, near San Pedro de Atacama, operates a submillimeter telescope (APEX). Moreover, a giant array of 12 m submillimeter antennas, called → ALMA, is being constructed in collaboration with North America, East Asia and Chile. ESO is currently planning a 42 m European Extremely Large optical/near-infrared Telescope, the → E-ELT.

See also: → European; → southern; → observatory.

An major intergovernmental research organisation in astronomy supported by 14 European countries. ESO was founded in 1962 as a consortium among Belgium, Denmark, France, Germany, the Netherlands, and Sweden. The ESO Headquarters are located in Garching near Munich, Germany. The organization operates three outstanding observing sites in the Atacama Desert region of Chile: → La Silla, → Paranal, and Chajnantor. The → Very Large Telescope (VLT), the world’s most advanced visible-light astronomical facility, is located on the 2600 m high mountain of Paranal, which also hosts the → VLT Interferometer (VLTI). The Chajnantor site, 5000 m above sea level, near San Pedro de Atacama, operates a submillimeter telescope (APEX). Moreover, a giant array of 12 m submillimeter antennas, called → ALMA, is being constructed in collaboration with North America, East Asia and Chile. ESO is currently planning a 42 m European Extremely Large optical/near-infrared Telescope, the → E-ELT.

See also: → European; → southern; → observatory.

An intergovernmental organisation dedicated to space research and technology as well as peaceful exploration of space, founded in 1975. It is headquartered in Paris and currently comprises 18 member states and one associated state (Canada). ESA has developed the Ariane series of space launch vehicles, and supports a launch facility in French Guiana. Moreover, ESA has four major research centers: The European Space Research and Technology Center (ESTEC), located in Noordwijk, the Netherlands, is the primary research center and manages the satellite projects. The European Space Operations Center (ESOC), situated in Darmstadt, Germany, is responsible for satellite control, monitoring, and data retrieval. The European Space Research Institute (ESRIN), located in Frascati, Italy, supports the ESA documentation service and manages the data obtained from remote sensing satellites. The European Astronaut Center (EAC), located in Cologne, Germany, is responsible for the selection and training of astronauts for space station missions. The European Space Astronomy Centre (ESAC), located in Villafranca del Castillo, Madrid, Spain, which holds scientific operations centres as well as archives. Some of the past ESA missions are the following ones. The Giotto space probe, which enabled examination of the core of → Halley’s Comet in 1986. ESA also developed the Ulysses spacecraft (launched 1990) to explore the Sun’s polar regions. Similarly, ESA established a system of meteorological satellites known as Meteosat. In 2003 ESA launched the Mars Express orbiter and its lander, Beagle 2. In 2009 ESA launched → Planck Satellite, that is designed to study the → cosmic microwave background, and the → Herschel Satellite, an infrared observatory that is the largest telescope in space.

Etymology (EN): → European; → space; agency, from M.L. agentia, from L. ag-, root of agere, → act + -entia noun suffix.

Etymology (PE): Sâzmân, → organization; fazâyi adj. of fazâ, → space; Orupâ, → Europa.

An intergovernmental organisation dedicated to space research and technology as well as peaceful exploration of space, founded in 1975. It is headquartered in Paris and currently comprises 18 member states and one associated state (Canada). ESA has developed the Ariane series of space launch vehicles, and supports a launch facility in French Guiana. Moreover, ESA has four major research centers: The European Space Research and Technology Center (ESTEC), located in Noordwijk, the Netherlands, is the primary research center and manages the satellite projects. The European Space Operations Center (ESOC), situated in Darmstadt, Germany, is responsible for satellite control, monitoring, and data retrieval. The European Space Research Institute (ESRIN), located in Frascati, Italy, supports the ESA documentation service and manages the data obtained from remote sensing satellites. The European Astronaut Center (EAC), located in Cologne, Germany, is responsible for the selection and training of astronauts for space station missions. The European Space Astronomy Centre (ESAC), located in Villafranca del Castillo, Madrid, Spain, which holds scientific operations centres as well as archives. Some of the past ESA missions are the following ones. The Giotto space probe, which enabled examination of the core of → Halley’s Comet in 1986. ESA also developed the Ulysses spacecraft (launched 1990) to explore the Sun’s polar regions. Similarly, ESA established a system of meteorological satellites known as Meteosat. In 2003 ESA launched the Mars Express orbiter and its lander, Beagle 2. In 2009 ESA launched → Planck Satellite, that is designed to study the → cosmic microwave background, and the → Herschel Satellite, an infrared observatory that is the largest telescope in space.

Etymology (EN): → European; → space; agency, from M.L. agentia, from L. ag-, root of agere, → act + -entia noun suffix.

Etymology (PE): Sâzmân, → organization; fazâyi adj. of fazâ, → space; Orupâ, → Europa.

A ductile silvery-white metallic → chemical element; symbol Eu. → Atomic number 63; → atomic weight 151.96;
→ melting point about 820°C;
→ boiling point about 1,600°C; → specific gravity 5.25 at 25°C. Europium occurs in monazite and bastnaesite and is used to dope → lasers and to absorb → neutrons in research. It was separated from the mineral samaria in magnesium-samarium nitrate by the French chemist Eugène-Anatole Demarçay (1852-1904) in 1901.

See also: Named after the continent Europe, → Europa.

A ductile silvery-white metallic → chemical element; symbol Eu. → Atomic number 63; → atomic weight 151.96;
→ melting point about 820°C;
→ boiling point about 1,600°C; → specific gravity 5.25 at 25°C. Europium occurs in monazite and bastnaesite and is used to dope → lasers and to absorb → neutrons in research. It was separated from the mineral samaria in magnesium-samarium nitrate by the French chemist Eugène-Anatole Demarçay (1852-1904) in 1901.

See also: Named after the continent Europe, → Europa.

Mixture of two substances which solidifies as a whole when cooled, without change in composition. The eutectic point is the temperature at which the eutectic mixture solidifies.

Etymology (EN): From Gk. eutektos “easily melted,” from → eu- + tektos “melted” + → -ic.

Etymology (PE): Hugodâz, from hu-, → eu-, + godâz, → melt.

Mixture of two substances which solidifies as a whole when cooled, without change in composition. The eutectic point is the temperature at which the eutectic mixture solidifies.

Etymology (EN): From Gk. eutektos “easily melted,” from → eu- + tektos “melted” + → -ic.

Etymology (PE): Hugodâz, from hu-, → eu-, + godâz, → melt.

The act or practice of putting painlessly to death, or allowing to die, especially in cases of incurable suffering.

Etymology (EN): From Gk. euthanasia “an easy or happy death,” from → eu- “good” + thanatos “death.”

Etymology (PE): Âsânmiri, literally “easy dyind,” from âsân, → easy,

• miri “dying,” from mordan “to die,” → death.

The act or practice of putting painlessly to death, or allowing to die, especially in cases of incurable suffering.

Etymology (EN): From Gk. euthanasia “an easy or happy death,” from → eu- “good” + thanatos “death.”

Etymology (PE): Âsânmiri, literally “easy dyind,” from âsân, → easy,

• miri “dying,” from mordan “to die,” → death.