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

The short-wavelength end of the hydrogen Lyman series, at 912 Å. Also called → Lyman continuum. It corresponds to the energy (13.6 eV) required for an electron in the hydrogen ground state to jump completely out of the atom, leaving the atom ionized.

→ Lyman; → limit.

A series of lines in the spectrum of hydrogen, emitted when electrons jump from outer orbits to the first orbit. The Lyman series lies entirely within the ultraviolet region. The brightest lines are Lyman-alpha at 1216 Å, Lyman-beta at 1026 Å, and Lyman-gamma at 972 Å.

→ Lyman; → series.

An → ultraviolet photon with an energy between 11.2 and 13.6 eV, corresponding to the energy range in which the Lyman and Werner absorption bands of → molecular hydrogen (H₂) are found (→ Lyman band, → Werner band). The first generation of stars produces a background of Lyman-Werner radiation which can → photodissociate molecular hydrogen, the key → cooling agent in metal free gas below 10⁴ K. In doing so, the Lyman-Werner radiation field delays the collapse of gaseous clouds, and thus star formation. After more massive → dark matter clouds are assembled, atomic line cooling becomes effective and H₂ can begin to shield itself from Lyman-Werner radiation.

→ Lyman; → Werner band; → photon.

The Lynx. A faint → constellation in the northern hemisphere that lies between → Auriga to the west and → Ursa Major to the east, at about 8h right ascension, 45° north declination. Abbreviation: Lyn; genitive: Lyncis.

From L. lynx, from Gk. lynx, probably from PIE *leuk-, → light, in reference to its gleaming eyes or its ability to see in the dark (cf. Lith. luzzis, O.H.G. luhs, Ger. Luchs, O.E. lox, Du. los, Swed. lo "lynx").

Siyâhguš "lynx," literally "black ear," from siyâh "black," from Mid.Pers. siyâ, siyâk, siyâvah "black," Av. sâma-, sayâva- "black, dark," cf. Skt. syama-, syava- "black, brown," Gk. skia "shadow" + guš, → ear.

In Saturn's rings, the gap between rings B and C.

Named after Bernard Lyot (1897-1952), French astronomer who discovered the division. He was also a distinguished solar observer and invented (1930) the → coronagraph; → division.

A type of narrow-band filter consisting of a series of birefringent crystals and polarizers invented by the French astronomer Bernard Lyot (1897-1952) for isolating and observing significant wavelengths of solar light.

→ Lyot division; → filter.

The Lyre. A small, bright constellation in the northern hemisphere at about 19h right ascension, 40° declination. The brightest star in Lyra is → Vega.

L. lyra, from Gk. lyra, a foreign word of uncertain origin.

Cang "harp," frpm Mid.Pers. cang "harp."

A meteor shower that occurs between 18 and 24 April. Its radiant is in the constellation → Lyra.

→ Lyra + → -ids.

The eleventh of Jupiter's known satellites; it is 36 km across and orbits Jupiter at a distance of about 11,720,000 km with a period of 259 days. It was discovered by S. Nicholson in 1938.

Lysithea was a daughter of Oceanus and one of Zeus' lovers.