An Etymological Dictionary of Astronomy and Astrophysics
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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.

→ type; → burst.

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

→ 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.

→ 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.

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

The → dust tail of a → comet.

→ type; → tail.

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

→ Type II supernova; L short for → linear.

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

→ 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).

→ 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.

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.

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

A → carbon star of the → asymptotic giant branch type located in the constellation of → Antlia. Its other designations are HIP 51821 (→ Hipparcos Star Catalogue), HD 91793, and HR 4153. U Antliae is an → irregular variable that changes its → visual magnitude between 5.27 and 6.04. About 850 → light-years from Earth, it shines with a → luminosity approximately 8,000 times that of the → solar luminosity and has a → surface temperature 2,800 K. It is surrounded by a complex structure of dust shells. Around 2,700 years ago, U Antliae went through a short period of rapid → mass loss. During this period of only a few hundred years, the material making up the shell seen in the → Atacama Large Millimeter Array (ALMA) data was ejected at high speed (Kerschbaum et al., 2017, A&A 605, A116, arXiv:1708.02915).

U, according to → variable star designation; → Antlia.

The prototypical and first discovered → cataclysmic variable. It is a → dwarf nova system with a relatively long → orbital period of 4 hr 17 minutes. U Gem undergoes → outbursts on time-scales between 30 and 250 days and shows → grazing occultations. The → accretion disk is partially eclipsed, but the → white dwarf remains visible during mideclipse. The mass of the white dwarf → primary is estimated to be 1.24 Msun, about two times higher than the mass of the → secondary; the → angle of inclination is 69°.7 (P. J. Groot 2001, ApJ 551, L89).

→ variable star designation; → Gemini.

Existing or being everywhere, especially at the same time; omnipresent.

From L. ubiquitarius, from ubique "everywhere," from ubi "where" + que "any, also, ever."

From visp-, → omni-, + bâšandé, bâš, bâšâ "existing, being," from budan "to be," → condition.

The state or capacity of being everywhere, especially at the same time; omnipresence.

From M.Fr. ubiquité, from L. ubique "everywhere," → ubiquitous; → -ity.

Noun from visp-bâšandé, visp-bâš, visp-bâšâyi, → ubiquitous.

A → photometric system which consists of measuring an object's → apparent magnitude through three broad-band filters: the ultraviolet (U) at 3650 Å, the blue (B) at 4400 Å, and the visual (V) in the green-yellow spectral region at 5500 Å. The filter bandwidths are 680, 980, and 890 Å respectively. The system is defined so that for A0 stars B - V = U - B = 0. The system was devised by Harold Johnson (1921-1980) and William Morgan (1906-1994) at Yerkes Observatory. It was extended to the R and I bands centered at 7000 and 9000 Å respectively and later to other infrared bands.

U, B, and V referring to "ultraviolet," "blue," and "visible" respectively; → system.

Short for → unidentified flying object.

→ unidentified flying object.

The act or occasion of catching sight of a UFO.

→ UFO; sighting, from sight, M.E. from O.E. sihth; cf. Dan. sigte, Swed. sigt, Du. zicht, O.H.G. siht, Ger. Sicht, Gesicht, related to see.

Didâr "sight, vision," verbal noun from didan "to see" (Mid.Pers. ditan "to see, regard, catch sight of, contemplate, experience;" O.Pers. dī- "to see;" Av. dā(y)- "to see," didāti "sees;" cf. Skt. dhī- "to perceive, think, ponder; thought, reflection, meditation," dādhye; Gk. dedorka "have seen").

A term that describes the collective efforts of those who study → unidentified flying object (UFO) reports.

Ufo, from → unidentified flying object; → -logy.

The question of the origin and nature of the → ultra high energy cosmic rays. According to the → GZK cutoff, the UHECRs should be nearby. They are expected to be exceptional, therefore visible by some astrophysical counterpart. However, there is nothing visible (within a few tens of → Mpc) in the direction of all the UHECR detected up to now.

→ UHECR; → puzzle.

Last; furthest or farthest; conclusive in a process or series; the highest or most significant.

L.L. ultimatus, p.p. of ultimare "to be final, come to an end," from L. ultimus "last, final, farthest, extreme," superlative of *ulter "beyond."

Ultom, from ul "up, upward," ulêh "upward, above," → ultra-, + -tom supelative suffix, → extreme.
Farjâmin "belonging to the end; concluding," from farjâm "end; conclusion," from Mid.Pers. farzâm "end; conclusion," farzâftan "to finish, to be perfect;" from Proto-Iranian *fra-gam- "to send; to finish" (cf. O.Pers. prāgama- "to go forth"), from *gam- "to go; to come;" cf. Av. gam- "to come; to go," jamaiti "goes;" O.Pers. gam- "to come; to go;" Mod./Mid.Pers. gâm "step, pace," âmadan "to come;" cf. Skt. gamati "goes;" Gk. bainein "to go, walk, step;" L. venire "to come;" Tocharian A käm- "to come;" O.H.G. queman "to come;" E. come; PIE root *gwem- "to go, come."

The future evolution of the → Universe which is a subject of study in → cosmology. The ultimate fate of the Universe can be explored using → general relativity. And since there is more than one possible solution to the equations of general relativity, there is more than one possible ultimate fate of the Universe. Moreover, the fate will depend on three factors: the Universe's overall shape or → geometry, its → dark energy content, and the → equation of state parameter. See also: → oscillating Universe, → Big Rip, → Big Crunch, → Big Freeze, → heat death.

→ ultimate; → Universe.