An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A series of → spectral lines in the → infrared spectrum of → neutral hydrogen emitted by electrons in → excited states transitioning to the level described by the → principal quantum number  n = 6. It begins at 12368 nm (Hu α 12.37 microns) and has been traced to 3281.4 nm (3.28 microns).

Named after Curtis J. Humphreys (1898-1986), American physicist; → series.

An empirical upper → luminosity boundary in the → H-R diagram. It consists of two sections, a sloping part and a horizontal part. The sloping part, which decreases with decreasing → effective temperature, corresponds roughly to the → Eddington limit. The horizontal part is the temperature-independent upper luminosity limit for late-type → hypergiants. It is thought that → massive stars above the Humphreys-Davidson limit encounter an → instability, possibly due to the opacity-modified Eddington limit, and experience high → mass loss episodes which prevent their evolution to cooler temperatures. → Luminous Blue Variable stars are examples of this high mass loss phase.

Named after Roberta M. Humphreys and Kris Davidson, who first dealt with this limit (1979, ApJ 232, 409); → limit.

An empirical rule stating that all orbitals of a given sublevel must be occupied by single electrons before pairing begins.

After the German physicist Friedrich Hund (1896-1997), known for his work on atoms and molecules. → rule.

The smallest three digit number in the decimal system and the smallest square of a two-digit number (10).

Hundred, from O.E. hundred "a counting of 100," from P.Gmc. *hunda- "hundred," as below, + *rath "reckoning, number."

Sad "hundred," from Mid.Pers. sad, sat, Av. sata- "hundred," satô.raocana- "with a hundred windows," satô.təmô.sata- "hundreds of hundred;" cf. Skt. śatá- "hundred;" Gk. hekaton; L. centum; Lith. simtas; P.Gmc. *hunda- "hundred" (Goth. hund; O.H.G. hunt); PIE *kmtom "hundred."

To chase or search for (game or other wild animals) for the purpose of catching or killing (Dictionary.com). See also → poach, → poaching.

M.E, hunten, from O.E. huntian "chase game," from hunta "hunter," and related to hentan "to pursue."

Šekâridan, šekâr kardan, from šekâr "hunt;" variant bešgar(d) "hunter, fowler; chase; game; place for hunting;" Parthian Mid.Pers. škr "to hunt, pursuit;" Sogdian škr-, (')škr- "to lead, take; pursue, persecute," prefixed 'pškr- "to chase;" Proto-Ir. *skar- "to pursue, drive, look for (the cattle);" + -gar, → -or.

A person who hunts game or other wild animals for food or in sport (Dictionary.com).

→ hunt; → -er.

A diagram where the surface → nitrogen  → chemical abundance of stars is plotted against their → projected rotational velocity (v sini).

I. Hunter et al., 2009, A&A, 496, 841; → diagram.

An intense warm-core oceanic cyclone that originates in tropical latitudes; called a typhoon in the western Pacific Ocean. Sustained winds are 120 km per hr or higher.

Hurricane, from Sp. huracán, from Taino (the language of an extinct Arawakan Indian tribe of the West Indies) hurakán.

Tufand, from tufidan "to roar, to raise a tumult," tufân "storm, the roaring of the sea, the confused hum of men or animals." Is this Persian word related to Gk. typhon "whirlwind," personified as a giant, father of the winds?

1) A state of urgency or eagerness; haste
2) (often followed by up) To move, proceed, or act with haste (Dictionary.com).

Of uncertain origin.

Tâveš, from Tâleši tâveš "hurry, haste," tâvisté "to hurry up;" variant Kurd. (Mahâbâd) tus "hasty."

Christiaan Huygens (1629-1695), an outstanding Dutch mathematician, astronomer, physicist, and horologist. → Huygens Division, → Huygens Region, → Huygens' principle, → Huygens-Fresnel principle.

In the system of → Saturn's rings, the gap at the inner edge of the → Cassini division at a distance of 117,680 km from the center of the planet with a width of 285-400 km.

→ Huygens; → division.

The inner bright part of the → Orion Nebula, from which most of the radiation is emitted. It is about 5' across corresponding to 0.7 pc (for a distance of 440 pc). See O'Dell (2001, ARAA 39, 99).

Named after the Dutch astronomer Christiaan → Huygens (1629-1695), who sketched the appearance of the Orion Nebula. His drawing, the first such known sketch, was published in Systema Saturnium in 1659. First named such by O. Gingerich (1982, Ann. NY Acad. Sci. 395, 308); → region.

Every point of a → wavefront may be considered as a center of a secondary disturbance which gives rise to spherical wavelets, and the wavefront at any later instant may be regarded as the envelope of these wavelets. This statement suffices to account for the laws of → reflection and → refraction, and the approximately straight line propagation of light through large apertures, but it fails to account for → diffraction, the deviations from exact straight line propagation of light. Huygens' principle was later extended by Fresnel and led to the formulation of → Huygens-Fresnel principle, which is of great importance in the theory of diffraction.

→ Huygens; → principle.

A development of → Huygens' principle stating that every point on a → wavefront acts, at a given instant, as a source of outgoing secondary spherical waves. The secondary wavelets mutually interfere and the resulting net light amplitude at any position in the outgoing wavefront is the vector sum of the amplitudes of all the individual wavelets. Using this principle, Fresnel calculated with a high accuracy the distribution of light in → diffraction patterns. The Huygens-Fresnel principle was put on a firm theoretical basis by Kirchhoff and expressed as an integral derived from the → wave equation.

→ Huygens; → Fresnel diffraction; → principle.

A young, nearby cluster of stars (spectral types A1-K) visible to the naked eye in the constellation → Taurus about 150 light-years away. Its individual stars (more than 200) appear to spread out in space. → Aldebaran is a foreground star in that region of the sky.

In Gk. mythology, a group of nymphs and sisters of Hyas, or else his daughters, and when Hyas died while hunting, killed by a lion or a boar, they grieved his death exceedingly, and turned into the stars called Hyades.

Huâdes, from Gk., as above.

Composed of two distinct races, breeds, varieties, species, or heterogeneous elements.

Hybrid, from L. hybrida, from ibrida "a crossbred animal," of unknown origin.

Doragé, literally "of two veins, races," from do, → two, + ragé, from rag "vein; lineage; race," → vessel.

A rare type of solar eclipse where at some places the eclipse is annular while at other places it appears total. This duality comes about when the vertex of the Moon's umbral shadow pierces Earth's surface at some points, but falls short of the planet along other portions of the eclipse path. Hybrid eclipses are also known as → annular-total eclipses. In most cases, hybrid eclipses begin as annular, transform into total, and then revert back to annular before the end of their track. In rare instances, a hybrid eclipse may begin annular and end total, or vice versa (F. Espenak, NASA).

→ hybrid; → eclipse.

A star on the upper → main sequence which simultaneously exhibits low-order pressure mode (→ p mode) and high-order gravity mode (→ g mode) characteristic of β Cephei and → slowly pulsating B stars, respectively. Examples include: γ Pegasi, HD 43317, and HD 50230.

→ hybrid; → pulsator.

A hypothetical object composed of a → quark matter in the central regions, enveloped by ordinary → hadronic matter.

→ hybrid; → star.

→ hydro-.