An Etymological Dictionary of Astronomy and Astrophysics

A multiple stellar system embedded in a → reflection nebula (NGC 6726/6727) in the → Corona Australis star forming region. The three stars are within 1.5 → astronomical units
of each other and lie at a distance of 129 pc. Two of its components form a → double-line eclipsing binary with an orbital period of almost 3 days. The primary is a → main sequence star (mass 3.16 solar masses, effective temperature 12,000 K)
and the secondary a → pre-main sequence star (mass 1.64 solar masses, effective temperature 4,900 K) with an age of a few million years. A third spectroscopic component is in a wide orbit around the eclipsing pair.
A fourth star is located at a projected distance of about 0.3 arcsecond (40 AU) from the compact tertiary system.

See also: → Corona Australis.

A multiple stellar system embedded in a → reflection nebula (NGC 6726/6727) in the → Corona Australis star forming region. The three stars are within 1.5 → astronomical units
of each other and lie at a distance of 129 pc. Two of its components form a → double-line eclipsing binary with an orbital period of almost 3 days. The primary is a → main sequence star (mass 3.16 solar masses, effective temperature 12,000 K)
and the secondary a → pre-main sequence star (mass 1.64 solar masses, effective temperature 4,900 K) with an age of a few million years. A third spectroscopic component is in a wide orbit around the eclipsing pair.
A fourth star is located at a projected distance of about 0.3 arcsecond (40 AU) from the compact tertiary system.

See also: → Corona Australis.

A → supernova of Type Ia in the constellation → Cassiopeia, which Tycho Brahe observed in November 1572. At its peak it was as bright as Venus and was visible in the daytime, reaching a magnitude of about -4. It is now visible as a → supernova remnant about 20 light-years across at a distance of about 7,500 light-years. It is associated with faint emission in the optical and X-rays, but is a strong radio source.
Other designations: SN 1572, 3C 10, B Cas, 2U 0022+63.

See also: Named after the Danish astronomer Tycho Brahe (1546-1601), who described the event; → star.

A → supernova of Type Ia in the constellation → Cassiopeia, which Tycho Brahe observed in November 1572. At its peak it was as bright as Venus and was visible in the daytime, reaching a magnitude of about -4. It is now visible as a → supernova remnant about 20 light-years across at a distance of about 7,500 light-years. It is associated with faint emission in the optical and X-rays, but is a strong radio source.
Other designations: SN 1572, 3C 10, B Cas, 2U 0022+63.

See also: Named after the Danish astronomer Tycho Brahe (1546-1601), who described the event; → star.

A hybrid of → geocentric and → heliocentric systems in which the Earth remains at the center, with the → Sun orbiting the Earth, but with all the other planets revolving about the Sun. Moreover, the fixed stars were located in a crystalline shell centered on the Earth.

See also: Related to the Danish astronomer Tycho Brahe (1546-1601), who imagined the model; → model.

A hybrid of → geocentric and → heliocentric systems in which the Earth remains at the center, with the → Sun orbiting the Earth, but with all the other planets revolving about the Sun. Moreover, the fixed stars were located in a crystalline shell centered on the Earth.

See also: Related to the Danish astronomer Tycho Brahe (1546-1601), who imagined the model; → model.

Thin brass disk inserted into the → mater of a → planispheric astrolabe. It carries the grid of → altazimuth coordinates shown in polar → stereographic projection for the → latitude of the specific observation locality. In addition to the main → vertical circles and the main → almucantars, the tympanum reproduces some elements of the → celestial sphere - the → celestial equator, the → tropic of Cancer, and the → tropic of Capricorn, as well as the hour lines for determining the unequal hours of day or night respectively from the Sun’s position on the ecliptic or from the altitude of a star marked on the → rete (online museo galileo, VirtualMuseum).

Etymology (EN): From L. tympanum “drum,” from Gk. tympanon “a drum, panel of a door,” from root of typtein “to beat, strike.”

Etymology (PE): Hojré, from Ar. hujrah “chamber.”

Thin brass disk inserted into the → mater of a → planispheric astrolabe. It carries the grid of → altazimuth coordinates shown in polar → stereographic projection for the → latitude of the specific observation locality. In addition to the main → vertical circles and the main → almucantars, the tympanum reproduces some elements of the → celestial sphere - the → celestial equator, the → tropic of Cancer, and the → tropic of Capricorn, as well as the hour lines for determining the unequal hours of day or night respectively from the Sun’s position on the ecliptic or from the altitude of a star marked on the → rete (online museo galileo, VirtualMuseum).

Etymology (EN): From L. tympanum “drum,” from Gk. tympanon “a drum, panel of a door,” from root of typtein “to beat, strike.”

Etymology (PE): Hojré, from Ar. hujrah “chamber.”

The observation whereby when light passes through a clear fluid holding small particles in suspension, the shorter blue wavelengths are scattered more strongly than the red. The effect is most commonly known as the → Rayleigh scattering.

See also: Names for John Tyndall (1820-1893), who discovered the effect in 1859.

The observation whereby when light passes through a clear fluid holding small particles in suspension, the shorter blue wavelengths are scattered more strongly than the red. The effect is most commonly known as the → Rayleigh scattering.

See also: Names for John Tyndall (1820-1893), who discovered the effect in 1859.

A group of items that have strongly marked and readily defined similarities.

Etymology (EN): M.E., from M.Fr., from L. typus “figure, image, form, kind,” from Gk. typos “dent, impression, mark, figure, original form,” from root of typtein “to strike, beat.”

Etymology (PE): Guné “species; color; form; manner, kind;” Mid.Pers. gônak “kind, species;” Av. gaona- “color; body hair;” PIE base *góur- “(animal) body hair,” genitive form *gunós.

A group of items that have strongly marked and readily defined similarities.

Etymology (EN): M.E., from M.Fr., from L. typus “figure, image, form, kind,” from Gk. typos “dent, impression, mark, figure, original form,” from root of typtein “to strike, beat.”

Etymology (PE): Guné “species; color; form; manner, kind;” Mid.Pers. gônak “kind, species;” Av. gaona- “color; body hair;” PIE base *góur- “(animal) body hair,” genitive form *gunós.

A type of → Seyfert galaxy showing both broad and narrow spectral emission lines. The widths of the broad lines indicates velocities around 1000 km s^-1. Sy 1 galaxies are also very bright sources of UV and X-ray emission.

See also: → type; → one; → Seyfert galaxy.

A type of → Seyfert galaxy showing both broad and narrow spectral emission lines. The widths of the broad lines indicates velocities around 1000 km s^-1. Sy 1 galaxies are also very bright sources of UV and X-ray emission.

See also: → type; → one; → Seyfert galaxy.

A type of → Seyfert galaxy showing only narrow emission lines and weak UV and X-ray emissions
but strong IR emission.

See also: → type; → two; → Seyfert galaxy.

A type of → Seyfert galaxy showing only narrow emission lines and weak UV and X-ray emissions
but strong IR emission.

See also: → type; → two; → Seyfert galaxy.

A burst of → X-rays observed toward → low-mass X-ray binary (LMXB)s. It is characterized by a sharp increase in → luminosity, which lasts 1-10 s, followed by the peak and a slow decrease, which can last from ~ 10s to 100s. Observationally, X-ray bursts manifest as a bright peak of emission on top of the persistent emission powered by → accretion. See also → Type II burst.

See also: → type; → burst.

A burst of → X-rays observed toward → low-mass X-ray binary (LMXB)s. It is characterized by a sharp increase in → luminosity, which lasts 1-10 s, followed by the peak and a slow decrease, which can last from ~ 10s to 100s. Observationally, X-ray bursts manifest as a bright peak of emission on top of the persistent emission powered by → accretion. See also → Type II burst.

See also: → type; → burst.

Statistics: An error made if a → hypothesis is rejected when it should be accepted. → Type II error.

See also: → type; → error.

Statistics: An error made if a → hypothesis is rejected when it should be accepted. → Type II error.

See also: → type; → error.

An → orbital migration of low-mass → planets in which no gap is created in the → protoplanetary disk. According to planetary models, beyond a critical core mass for the forming planet, a gap in the protoplanetary disk is created. The critical mass depends on the mass and → metallicity of the disk and therefore it does not have a singular value, but has been shown to be between about 10-30 Earth masses. Compare with → Type II migration.

See also: → type; → migration.

An → orbital migration of low-mass → planets in which no gap is created in the → protoplanetary disk. According to planetary models, beyond a critical core mass for the forming planet, a gap in the protoplanetary disk is created. The critical mass depends on the mass and → metallicity of the disk and therefore it does not have a singular value, but has been shown to be between about 10-30 Earth masses. Compare with → Type II migration.

See also: → type; → migration.

A type of supernova whose spectra lacks hydrogen lines. Its → light curve exhibits a sharp maximum with a gradual decrease. Typical magnitudes M_V = -14 to -17. Ejecta velocities about 10,000 km/sec. Type I supernovae have several subtypes: → Type Ia, → Type Ib, and → Type Ic.

See also: Type I initially introduced by R. Minkowski (1941, PASP 53, 224); → type; → supernova.

A type of supernova whose spectra lacks hydrogen lines. Its → light curve exhibits a sharp maximum with a gradual decrease. Typical magnitudes M_V = -14 to -17. Ejecta velocities about 10,000 km/sec. Type I supernovae have several subtypes: → Type Ia, → Type Ib, and → Type Ic.

See also: Type I initially introduced by R. Minkowski (1941, PASP 53, 224); → type; → supernova.

The → gas tail of of a comet.

See also: → type; → tail.

The → gas tail of of a comet.

See also: → type; → tail.

A → Type I supernova that presents a singly-ionized silicon (Si II) absorption feature at 6150 Å near peak brightness. Type Ia SNe
are believed to result from mass → accretion to a carbon-oxygen → white dwarf in a → close binary system. When the white dwarf mass exceeds the → Chandrasekhar limit, the → degenerate electron pressure can no longer support the accumulated mass and the star collapses in a thermonuclear explosion producing a supernova. The → peak luminosity of SNe Ia is set by the radioactive decay chain ⁵⁶Ni → ⁵⁶Co → ⁵⁶Fe, and the observed photometric correlation between the peak luminosity and the time-scale over which the → light curve decays from its maximum is understood physically as having both the luminosity and → opacity being set by the mass of ⁵⁶Ni synthesized in the explosion.
Type Ia supernovae occur in all types of galaxies. Type Ia SNe are used as → standard candles in determining cosmological distances, after normalizing their light curves with the → Phillips relation.

See also: → type; → supernova.

A → Type I supernova that presents a singly-ionized silicon (Si II) absorption feature at 6150 Å near peak brightness. Type Ia SNe
are believed to result from mass → accretion to a carbon-oxygen → white dwarf in a → close binary system. When the white dwarf mass exceeds the → Chandrasekhar limit, the → degenerate electron pressure can no longer support the accumulated mass and the star collapses in a thermonuclear explosion producing a supernova. The → peak luminosity of SNe Ia is set by the radioactive decay chain ⁵⁶Ni → ⁵⁶Co → ⁵⁶Fe, and the observed photometric correlation between the peak luminosity and the time-scale over which the → light curve decays from its maximum is understood physically as having both the luminosity and → opacity being set by the mass of ⁵⁶Ni synthesized in the explosion.
Type Ia supernovae occur in all types of galaxies. Type Ia SNe are used as → standard candles in determining cosmological distances, after normalizing their light curves with the → Phillips relation.

See also: → type; → supernova.

A → Type I supernova that has neutral helium line (He I) at 5876 Å, and no strong silicon (Si II) absorption feature at 6150 Å. Type Ib supernovae are believed to result from the evolution of → massive stars.

See also: → type; → supernova.

A → Type I supernova that has neutral helium line (He I) at 5876 Å, and no strong silicon (Si II) absorption feature at 6150 Å. Type Ib supernovae are believed to result from the evolution of → massive stars.

See also: → type; → supernova.

A → Type I supernova that shows weak or no helium lines and no strong silicon (Si II) absorption feature near 6150 Å. Type Ic supernovae are believed to result from the evolution of → massive stars.

See also: → type; → supernova.

A → Type I supernova that shows weak or no helium lines and no strong silicon (Si II) absorption feature near 6150 Å. Type Ic supernovae are believed to result from the evolution of → massive stars.

See also: → type; → supernova.

A burst of → X-rays observed toward → low-mass X-ray binary (LMXB)s and characterized by quick succession of bursts with recurrence intervals as short as ~ 7 s. Type II X-ray bursts look similar to → Type I bursts, but they are thought to be related with spasmodic episodes of → accretion.

See also: → type; → burst.

A burst of → X-rays observed toward → low-mass X-ray binary (LMXB)s and characterized by quick succession of bursts with recurrence intervals as short as ~ 7 s. Type II X-ray bursts look similar to → Type I bursts, but they are thought to be related with spasmodic episodes of → accretion.

See also: → type; → burst.

Statistics: An error made if a → hypothesis is accepted when it should be rejected. → Type I error.

See also: → type; → error.

Statistics: An error made if a → hypothesis is accepted when it should be rejected. → Type I error.

See also: → type; → error.

The → orbital migration of forming → planets that → accrete
enough disk material to exceed the critical mass. This type migrates in a gap created in the → protoplanetary disk. Compare with → Type I migration.

See also: → type; → migration.

The → orbital migration of forming → planets that → accrete
enough disk material to exceed the critical mass. This type migrates in a gap created in the → protoplanetary disk. Compare with → Type I migration.

See also: → type; → migration.

A supernova type whose spectrum contains hydrogen lines. Compared with → Type I supernovae, its → light curve has a broader peak at maximum and dies away more rapidly. The magnitudes are smaller, ranging from M_V = -12 to -13.5, and the ejecta have lower velocities (about 5,000 km/sec). These supernovae, which result from the final evolution of
→ massive stars, have three main divisions: → Type II-P, → Type II-L, and → Type II-n.

See also: Type II initially introduced by R. Minkowski (1941, PASP 53, 224); → type; → supernova.

A supernova type whose spectrum contains hydrogen lines. Compared with → Type I supernovae, its → light curve has a broader peak at maximum and dies away more rapidly. The magnitudes are smaller, ranging from M_V = -12 to -13.5, and the ejecta have lower velocities (about 5,000 km/sec). These supernovae, which result from the final evolution of
→ massive stars, have three main divisions: → Type II-P, → Type II-L, and → Type II-n.

See also: Type II initially introduced by R. Minkowski (1941, PASP 53, 224); → type; → supernova.

The → dust tail of a → comet.

See also: → type; → tail.

The → dust tail of a → comet.

See also: → type; → tail.

A → Type II supernova which displays a linear decrease in its → light curve.

See also: → Type II supernova; L short for → linear.

A → Type II supernova which displays a linear decrease in its → light curve.

See also: → Type II supernova; L short for → linear.

A → Type II supernova which shows intermediate or very narrow width hydrogen → emission lines in the spectra.

See also: → Type II supernova; n short for → narrow.

A → Type II supernova which shows intermediate or very narrow width hydrogen → emission lines in the spectra.

See also: → Type II supernova; n short for → narrow.

A → Type II supernova which reaches a plateau in its → light curve. The vast majority of Type II SNe are characterized by a fast (few days) rise to a flat light curve, most pronounced in the reddest optical bands, with a duration of 80-100 days. This plateau phase is interpreted as the recession of the photosphere as the ejecta expand and cool. The spectra of SNe II-P are typically dominated by strong
→ P Cygni profiles of hydrogen lines, as well as iron absorption features (for a review, e.g., see Filippenko 1997, ARA&A 35, 309).

See also: → Type II supernova; P short for → plateau.

A → Type II supernova which reaches a plateau in its → light curve. The vast majority of Type II SNe are characterized by a fast (few days) rise to a flat light curve, most pronounced in the reddest optical bands, with a duration of 80-100 days. This plateau phase is interpreted as the recession of the photosphere as the ejecta expand and cool. The spectra of SNe II-P are typically dominated by strong
→ P Cygni profiles of hydrogen lines, as well as iron absorption features (for a review, e.g., see Filippenko 1997, ARA&A 35, 309).

See also: → Type II supernova; P short for → plateau.

Having all or most of the characteristics shared by others of the same kind and therefore suitable as an example of it.

Etymology (EN): From M.L. typicalis “symbolic,” from L.L. typicus “of or pertaining to a type,” from Gk. typikos, from typos “impression,” from typ(os) + -ikos, → -ic.

Etymology (PE): Gune-vâr, from guné, → type, + -vâr a suffix meaning “resembling, like” (Mid.Pers. -wâr, Av. -vara, -var, cf. Skt. -vara).

Having all or most of the characteristics shared by others of the same kind and therefore suitable as an example of it.

Etymology (EN): From M.L. typicalis “symbolic,” from L.L. typicus “of or pertaining to a type,” from Gk. typikos, from typos “impression,” from typ(os) + -ikos, → -ic.

Etymology (PE): Gune-vâr, from guné, → type, + -vâr a suffix meaning “resembling, like” (Mid.Pers. -wâr, Av. -vara, -var, cf. Skt. -vara).