An Etymological Dictionary of Astronomy and Astrophysics
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An unstable elementary particles, belonging to the class called → baryons, which have greater mass than the neutron but very short lives (10^-8 to 10^-10 seconds).

From → hyper- + → -on a suffix used in the names of elementary particles (gluon; meson; neutron; graviton, and so on).

In aerodynamics, adjective used to describe a → sound speed in excess of Mach 5. See also → supersonic.

Hypersonic, from → hyper- + → sonic.

A star whose velocity is so great that it will escape the → gravitational potential of our → Galaxy. Depending on the location and direction of motion, this criterion typically corresponds to a stellar velocity in the Galactic → rest frame larger than 400 km s^-1, and up to about 1200 km s^-1. The nature of the HVSs spans a wide range of types from → OB stars, to metal-poor → F-type stars and G/K dwarfs. While there is evidence from many late-type B HVSs in the → halo to originate from the Galactic → supermassive black hole (SMBH), other HVSs seem to originate from the → galactic disk. HVSs can obtain their large velocities from a number of different processes:
1) → Tidal disruption of → close binary stars by the central SMBH of the Milky Way. In this process one star is captured by the SMBH while the other is ejected at high speed via the → gravitational slingshot mechanism.
2) Exchange encounters in other dense stellar environments between hard binaries (→ hard binary) and → massive stars may cause stars to be ejected and escape our Galaxy.
3) Disruption of close binaries via → supernova explosions. The → runaway velocities of both ejected stars can reach large values when asymmetric supernovae are considered, i.e. when the newborn → neutron star receives a momentum kick at birth.
(see, e.g., T. M. Tauris, 2014, and references therein, arXiv:1412.0657).

→ hyper-; → velocity; → star.

A Gk. prefix denoting "under."

Gk. hypo "under" (prep.), "below" (adv.); cognate with L. sub- and O.Pers./Av. upā, as below.

Upâ-, from O.Pers. upā (prep.) "under, with;" Av. upā, upa (prep.; prevb) "toward, with, on, in" (upā.gam- "to arrive at," upāpa- "living in the water," upa.naxturušu "bordering on the night"); Mod.Pers. bâ "with," from abâ; cf. Skt. úpa (adv., prevb., prep.) "toward, with, under, on;" cognate with Gk. hypo, as above.

A curve generated by the trace of a fixed point on a small circle that rolls within a larger circle.

Hypocycloid, from → hypo- + → cycloid.

In a → right triangle, the side opposite to the right angle.

L.L. hypotenusa, from Gk. hypoteinousa "stretching under" (the right angle), from hypoteinein, from → hypo- "under" + teinein "to stretch," → tension.

Vatar loan from Ar.

The failure of the body to maintain adequate production of heat under conditions of extreme cold.

Hypothermia, from → hypo- + therm, from Gk. therme "heat," from PIE *ghwerm-/*ghworm- "warm;" cf. Pers. garm "warm;" L. fornax "an oven;" O.E. wearm "warm" + -ia a noun suffix.

Upâgarmâyi, from upâ-, → hypo-, + garmâ "heat, warmth," from Mid.Pers. garmâg; O.Pers./Av. garəma- "hot, warm;" cf. Skt. gharmah "heat;" Gk. thermos "warm;" L. formus "warm," fornax "oven;" P.Gmc. *warmaz; O.E. wearm; E. warm; O.H.G., Ger. warm; PIE *ghworm-/*ghwerm- "warm" + -yi noun suffix.

A statement which is based on previous observations and which serves as a starting point for further investigation by which it may be proved or disproved. See also → theory, → model, → ad hoc hypothesis, → Kant-Laplace hypothesis, → arge number hypothesis, → nebular hypothesis, → null hypothesis, → statistical hypothesis, → statistical hypothesis testing.

Hypothesis, from M.Fr. hypothèse, from L.L. hypothesis, from Gk. hypothesis "base, basis of an argument, supposition," literally "a placing under," from → hypo- "under" + thesis "a placing, proposition," from root of tithenai "to place, put, set," didomi "I give;" from PIE base *dhe- "to put, to do;" cf. Mod.Pers. dâdan "to give," Mid.Pers. dâdan "to give," O.Pers./Av. dā- "to give, grant, yield," dadāiti "he gives;" Skt. dadáti "he gives;" L. dare "to give, offer," facere "to do, to make;" Rus. delat' "to do;" O.H.G. tuon, Ger. tun, O.E. don "to do."

Engâré, from engâridan, engâštan "to → suppose."
Upâdâyan, from upâ-, → hypo-, + dâyan, → thesis.

To form a → hypothesis.

Hypothesize, from hypothes(is), → hypothesis + -ize a verb-forming suffix, from M.E. -isen, from O.Fr. -iser, from L.L. -izare, from Gk. -izein.

Engâré sâxtan, from engâré, → hypothesis + sâxtan, sâzidan "to adapt, adjust, be fit; to build, make, fashion," Mid.Pers. sâxtan, sâz-, Manichean Parthian s'c'dn "to prepare, to form," Av. sak- "to understand, to mark," sâcaya- (causative) "to teach."
Upâdâyanidan, infinitive from upâdâyan, → hypothesis.

Of, pertaining to, or involving a → hypothesis; supposed.

→ hypothesis; → -al.

The phenomenon exhibited by a body (especially a ferromagnetic or imperfectly elastic material) in reacting to changes in the forces, especially magnetic forces, affecting it.
In ferromagnetic materials, the lag in the change in the magnetic induction B behind the change in the intensity of the external magnetizing field, due to the dependence of B on its previous values (past history).

Hysteresis, from Gk. hysteresis "being behind or late," from hystere-, stem of hysterein "to come late, lag behind" + -sis a suffix forming abstract nouns of action.

Pasmând "lagging behind," from pas "behind" (Mid.Pers. pas "behind, before, after;" O.Pers. pasā "after;" Av. pasca "behind (of space); then, afterward (of time);" cf. Skt. pazca "behind, after, later," L. post "behind, in the rear; after, afterward;" O.C.S. po "behind, after;" Lith. pas "at, by;" PIE *pos-, *posko-) + mând stem of mândan "to remain; to be fatigued," mân "house, family" (Mid.pers. mândan "to remain, stay;" O.Pers. mān- "to remain, dwell;" Av. man- "to remain, dwell; to wait;" cf. Gk. menein "to remain;" L. manere "to stay, remain, abide," mansio "a staying, a remaining, night quarters, station" (Fr. maison, ménage; E. manor, mansion, permanent); PIE *men- "to remain, wait for."

A closed curve showing the change in magnetic induction of a ferromagnetic body to which an external field is applied as the intensity of this field is varied from +H_s to -H_s and back again, where H_s is the magnetic field intensity corresponding to saturation.

→ hysteresis; → loop.

Dissipation of energy which occurs, due to magnetic hysteresis, when the magnetic material is subject to changes of magnetization.

→ hysteresis; → loss.

The seventeenth of Saturn's known satellites and the third largest. It is 1436 km across and revolves around Saturn at a mean distance of 3.5 million km with a period of 79 days. The most unique and perhaps most remarkable feature on Iapetus is a topographic ridge 13 km higher than the surrounding terrain, as discovered in the images obtained with Cassini spacecraft. The ridge extends at least 1300 km almost exactly parallel with Iapetus's equator.

Iapetus was one of the Titan gods, sons of Ouranos (Heaven) and Gaia (Earth). Discovered 25 October 1671 by Jean-Dominique Cassini.

A small → dwarf irregular galaxy belonging to the → Local Group, which is located in the constellation → Cassiopeia. IC 10 is about 2.3 million light-years distant and about 5,000 light-years across. With an absolute B magnitude of -16.5, IC 10 has an integrated luminosity that is comparable to that of the → Small Magellanic Cloud, although it is considerably smaller. Its → metallicity is roughly a factor of 2 higher than that of the SMC and in the same proportion smaller than → LMC's. Compared to other Local Group galaxies, IC 10 has a large population of newly formed stars that are massive and intrinsically very bright, especially → Wolf-Rayet stars. Its W-R star density is larger than those of the LMC and SMC. Moreover, the relative number of known → WC to → WN type Wolf-Rayet stars is unusually high, which is unexpected for IC 10's metallicity. IC 10 is also known to be unusual in having → H I gas that extends about 7 times the optical dimensions of the galaxy. IC 10 is the nearest example of a → starburst galaxy. IC 10 was discovered by the American astronomer Lewis A. Swift (1820-1913) in 1887.

Number 10 in the → Index Catalogue.

A → dwarf irregular galaxy (also called Caldwell 51) located in the constellation → Cetus. IC 1613 is a member of the → Local Group of galaxies and has a → morphological classification of IBm (Irregular Barred, → Magellanic type galaxy). IC 1613 has a very → low surface brightness and a very low → dust content. It lies just over 2.38 ± 0.07 million → light-years away from us. IC 1613's distance is known to a remarkably high precision, partly due to the unusually low levels of dust lying both within the galaxy and along the line of sight from the → Milky Way. Moreover, the galaxy hosts a number of → Cepheid variables and → RR Lyrae variables which can be used to precisely determine distances. It was discovered by Max Wolf in 1906.

IC, short for → Index Catalogue.

A bright → emission nebula running north to south near → Alnitak, the eastern star of → Orion's Belt. It is the bright background nebula against which the famous dark region called the → Horsehead Nebula stands out.

IC, → Index Catalogue.

1) The solid form of water; it is found in the atmosphere as snow crystals, hail, ice pellets, etc., and on the Earth's surface in forms such as frost, rime, glaze, glacier ice, etc.
2) The solid, frozen form of gases in cold astronomical objects.

Ice, from O.E. is "ice," from P.Gmc. *isa-; cf. O.N. iss, O.Fris. is, Du. ijs, Ger. Eis. Cognate with Pers. yax, as below.

Yax, from Av. aexa- "ice, frost," isav-, isu- "icy, chilly;" cf. Sarikoli (Pamir dialect) īš "cold;" P.Gmc. *isa-, as above.

Meteo.: The process by which a layer of ice builds up on solid objects that are exposed to freezing precipitation or to supercooled fog or cloud droplets.

→ ice; → accretion.

A major interval of geologic time during which extensive ice sheets (continental → glaciers) formed over many parts of the world. There have been at least five significant ice ages in Earth's history, with approximately a dozen epochs of glacial expansion occurring in the past 1 million years. The last one ran from about 75,000 to 15,000 years ago.

→ ice; → age.