An Etymological Dictionary of Astronomy and Astrophysics
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An approximate expression for deriving the → opacity that depends upon temperature with a power law: κ ∝ ρT^-3.5, where ρ represents the density. In → partial ionization zones, a part of the energy released during a layer's compression can be used for further ionization, rather than raising the temperature of the gas. As the temperature of the compressed layer has not substantially increased, the increase in density produces a corresponding increase in the opacity of the layer. Likewise, during the expansion phase, the temperature does not decrease significantly since the ions release energy when they recombine with electrons.

Derived in 1923 by the Dutch physicist Henrik Kramers (1894-1952); → law.

Same as → Kramers' law.

Named after Henrik Kramers (1894-1952); → law.

The function δⁱ_k of two variables i and j defined by δⁱ_k = 1 if i = j, and δⁱ_k = 0 if i ≠ j.

Leopold Kronecker (1823-1891), a German mathematician; delta, Gk. letter of alphabet.

A diagram used to plot trajectories in → space-time near a → black hole. The vertical and horizontal axes are two complicated functions of time and distance from the black hole. Lines of constant time radiate from the origin of the diagram, with steeper slopes corresponding to later times. Lines of constant distance are hyperbolas, lines of constant time pass through the origin; photons always travel along diagonal lines at ±45° to the vertical. The trajectory of an object falling into the black hole is shown as a curving line moving upward on the diagram at less than 45° to the vertical.

Named after the American physicist Martin David Kruskal (1925-2006); → diagram.

A colorless, odorless, highly un-reactive gaseous chemical element and a member of the inert gas family. Symbol Kr; atomic number 36; atomic weight 83.80; melting point -156.6°C; boiling point -152.3°C.

Krypton, from Gk. kryptos "concealed, hidden". It was discovered in liquefied atmospheric air by the Scottish chemist William Ramsay and the English chemist Morris William Travers in 1898.

A region of the → Solar System extending roughly from the orbit of → Neptune, or 30 → astronomical units (AU), to 50 AU from the Sun that contains many small icy bodies. The Kuiper belt is now considered to be the source of the → short-period comets.

Named after Gerard Peter Kuiper (1905-1973), a Dutch-born American astronomer, who predicted the belt in 1951. He is also considered the father of modern planetary science for his contributions to the study of our solar system; → belt.

A → Solar System object belonging to the → Kuiper belt. The largest known objects of this type are → Pluto and its moon → Charon, → Quaoar, → Sedna, and → Orcus. See also → trans-Neptunian object.

→ Kuiper belt; → object.

The measure of "peakedness" of the curve describing a frequency distribution in the region about its mode. The kurtosis of the normal distribution is 0.

From Gk. kurtosis "bulging, curvature," from kurtos "convex," kirkos "a ring;" cf. Av. skarəna- "round;" L. circus "circle, ring;" PIE base *sker- "to turn, bend."

Afrâštegi condition, state adj. of afrâšté "elevated, erect, upright," p.p. of afrâštan "to raise, exalt, extole," from Mid.Pers. abrâstan, abrâz- "to lift, raise," from ab-, from O.Pers./Av. abiy-/aiwi- "to, upon, against;" cf. Skt. abhi-, Gk. amphi- + râst "straight, direct, true;" from O.Pers. rāsta- "straight, true," rās- "to be right, straight, true;" Av. rāz- "to direct, put in line, set," razan- "order;" cf. Skt. raj- "to direct, stretch," rjuyant- "walking straight;" Gk. orektos "stretched out;" L. regere "to lead straight, guide, rule," p.p. rectus "right, straight;" Ger. recht; E. right; PIE base *reg- "move in a straight line," hence, "to direct, rule."

A type of → brown dwarf with an → effective temperature ranging from about 2200 K to about 1300 K, corresponding to luminosities about 4 x 10^-4 to 3 x 10^-5 times that of the Sun. L dwarfs are intermediate in temperature between M and → T dwarfs. Their spectra in the optical show weak titanium oxide (TiO) and vanadium oxide (VO) absorption lines and strong metallic hydrides CrH (8611 and 9969 Å) and FeH (8692 and 9896 Å). Also are present strong neutral atomic lines of alkali metals Na I (8183, 8195 Å), K I (7665, 7699 Å), Rb I (7800, 7948 Å), Cs I (8521, 8943 Å), and sometimes Li I (6708 Å). The prototype of the L-dwarf class is → GD 165B. The spectral classification was first defined by Kirkpatrick et al. 1999, ApJ 519, 802 and Martin et al. 1999, AJ 118, 2466.

For the reasoning behind the choice of the letter L, see Kirkpatrick et al. 1993, ApJ 406, 701; → dwarf.

A → semiregular variable with a period of 141 days. It has a → spectral type of M5 III corresponding to an → effective temperature of ~ 3500 K. It has a radial velocity relative to the → Local Standard of Rest of 33.3 km s^-1. At a distance of 64 → parsecs, L₂ Pup is the second nearest → asymptotic giant branch (AGB) star next to R Doradus; it is ~ 30% closer than → Mira. Recent → near-infrared JHKL band observations by Kervella et al. (2014, 2015) show a compact dust disk around the central star, with an inner rim of 6 → astronomical units and an outer edge of 13 au, at an inclination of approximately 82°. The → circumstellar environment of L₂ Pup was observed with → ALMA. The → molecular emission shows a → differentially rotating disk, inclined to a nearly edge-on position (Homan et al., 2017, A&A 601, A5 and references therein).

Star name in the → Bayer designation scheme; → Puppis.

La Niña. A condition in which a significant decrease (more than 0.5 °C from average water temperatures) occurs in sea surface temperature (cold event) in the central and eastern equatorial Pacific. La Niña has a natural 3-6 year cycle and can persist for 1-3 years. It is the counterpart to the → El Nino (warm event), and its spatial and temporal evolution in the equatorial Pacific is, to a considerable extent, the mirror image of El Niño, although La Niña events tend to be somewhat less regular in their behavior and duration.

American Sp. La Niña "the girl," to distinguish it from → El Nino.

The site of the → European Southern Observatory's first observatory in Chile, inaugurated in 1969. It is located 160 km north of the town of La Serena and 600 km north of Santiago at an altitude of 2,400 m bordering the southern extremity of the Atacama Desert. La Silla is equipped with several optical telescopes with mirror diameters of up to 3.6 m. The 3.5 m New Technology Telescope was the first in the world to have a computer-controlled main mirror, a technology developed at ESO. The ESO 3.6 m telescope is now home to the world's largest extrasolar planet hunter: HARPS (High Accuracy Radial velocity Planet Searcher), a spectrograph with unrivalled precision.

From Sp. la silla "the saddle," after the apparent shape of the mountain on which the observatory is situated. Originally known as Cinchado.

A building or place equipped for carrying out scientific research, experimentation, investigation, observation, etc.

M.L. laboratorium "a place for labor or work," from L. laboratus, p.p. of laborare "to work."

Âzmâyešgâh, from âzmâyeš, → experiment, + -gâh "place, time," → university.

The Lizard. A small constellation in the northern hemisphere, at about 22h right ascension, 45° north declination. Its brightest star is only of magnitude +3.8, and the constellation contains no other star above fourth magnitude. Its most famous object is BL Lacerta, the prototype → BL Lac objects. Abbreviation: Lac; genitive: Lacertae.

From L. lacertus (fem. lacerta) "lizard," of unknown origin.

Calpâsé "lizard," variants karpâsa, karisa, kelpasa; cf. Skt. krakacapad- "saw-footed, a lizard, chameleon," from krakaca- "saw" + pad "foot" (Pers. pâ).

1a) Deficiency or absence of something needed, desirable, or customary.
1b) Something missing or needed. See also → default, → deficiency, → shortage.
2a) (v.tr.) To be without or deficient in; to fall short in respect of.
2b) (v.intr.) to be absent or missing, as something needed or desirable (Dictionary.com).

M.E. lak; cognate with M.L.G. lak, M.Du. lac "deficiency;" akin to O.Norse lakr "deficient."

Nast, from negation prefix na- "in-, non," → not, + ast, hast "is," from astan, hastan "to be," → exist.

Absent; wanting; deficient.

→ lack; → -ing.

1) A piece of equipment consisting of a series of bars or steps between two upright lengths of wood, metal, or rope, used for climbing up or down something.
2) A series of ascending stages by which someone or something may progress (OxfordDictionaries.com).

M.E. laddre, O.E. hlæder "ladder, steps" (cognates: M.Du. ledere, O.H.G. leitara, Ger. Leiter), from PIE root *klei- "to lean," → incline.

Nardebân "ladder."

1a) A lagging or falling behind; retardation.
1b) Mechanics: The amount of retardation of some motion.
1c) Electricity: The retardation of one alternating quantity, as current, with respect to another related alternating quantity, as voltage.
2) To fail to maintain a desired pace or to keep up; fall or stay behind (Dictionary.com).

Possibly from Scandinavian; cf. Norwegian lagga "to go slowly."

Lek, from lek lek kardan "to walk slowly, to lag behind."

1) A body of seawater that is almost completely cut off from the ocean by a barrier beach.
2) The body of seawater that is enclosed by an atoll.

Lagoon, from Fr. lagune, from It. laguna "pond, lake," from L. lacuna "pond, hole," from lacus "pond;" → nebula.

Mordâb "lagoon," literally "dead water," from mord, mordé "dead" + âb "water."
The first element from mordan, mir- "to die," marg "death," mard "man;" Mid.Pers. murdan "to die;" O.Pers. marta- "dead," martiya- "man;" Av. mərəta- "died, dead," amərətāt- "immortality;" cf. Skt. mar- "to die," mriyáe "dies;" Gk. emorten "to die," ambrotos "immortal;" L. morior "to die" (Fr. mourir), mors, mortis "death" (Fr. mort), immortalis "immortal;" Lith. mirtis "mortal;" O.C.S. mrutvu "dead;" O.Ir. marb; Welsh marw "died;" O.E. morþ "murder;" PIE base *mor-/*mr- "to die."
The second element âb "water," from Mid.Pers. âb "water;" O. Pers. ap- "water;" Av. ap- "water;" cf. Skt. áp- "water;" Hitt. happa- "water;" PIE āp-, ab- "water, river;" cf. Gk. Apidanos, proper noun, a river in Thessalia; L. amnis "stream, river" (from *abnis); O.Ir. ab "river," O.Prus. ape "stream," Lith. upé "stream;" Latv. upe "brook."

A giant → H II region lying in the direction of → Sagittarius about 5,000 → light-years away. It represents a giant cloud of interstellar matter which is currently undergoing star formation, and has already formed a considerable cluster of young stars (NGC 6530).

→ lagoon; → nebula.