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

A → supercluster of galaxies that includes our → Local Group and about 300 to 500 known → galaxy clusters and groups. Also called → Local Supercluster. If approximated as round, it has a diameter of 12,000 km s^-1 in units of the → cosmic expansion or 160 megaparsecs, and encompasses about 10¹⁷ → solar masses. Our Local Group lies toward the outer regions of Laniakea. Its main components are the four previously known superclusters: → Virgo supercluster (the part where the → Milky Way resides), Hydra-Centaurus Supercluster (including the → Great Attractor, Antlia Wall, known as Hydra Supercluster, → Centaurus supercluster), Pavo-Indus Supercluster, and Southern Supercluster (including Fornax Cluster, Dorado and Eridanus clouds). The most massive galaxy clusters of Laniakea are Virgo, Hydra, Centaurus, Abell 3565, Abell 3574, Abell 3521, Fornax, Eridanus, and Norma. The Laniakea supercluster was discovered by Tully et al. (2014, Nature 513, 71).

From the Hawaiian words lani "heaven," and akea "spacious, immeasurable;" → supercluster.

A bright blue star of → apparent visual magnitudeV = 2.70, that with → Shaula (Lambda Scorpii) makes up the Scorpion's stinger. Among its other designations: HR 6508 and HIP 85696. Lesath is 580 → light-years away. Lesath and Shaula appear very close on the sky (less than a degree apart), but they are not physically related. Lesath is a → subgiant of → spectral type B2 IV with a → luminosity of about 7,380 Msun. It has a radius of about 6 Rsun, and a → surface temperature of about 22,000 K.

Lesath, from Ar. al-Las'ah (اللسعه) "the sting."

A system of three charges +q, -2q, and +q, arranged along a line to form an axial quadrupole. The → electric potential  V due to a linear quadrupole varies as 1/r³, whereas the → electric intensity  E varies as 1/r⁴.

→ linear; → electric; → quadrupole.

A small → galaxy cluster of about 50 galaxies to which our → Milky Way galaxy belongs. The Local Group occupies a volume of space nearly 10 million → light-years across centered somewhere between the → Andromeda Galaxy (M31) and the Milky Way, which are the dominant galaxies of the group; Andromeda being the principal member. Both of these galaxies exhibit spiral structures, and each is attended by a large family of satellite → dwarf galaxies. The Local Group also includes a third spiral galaxy known as → Triangulum (M33), which is bound to Andromeda. The remaining members span a range of → Hubble classification types from dwarf spheroidal to Irr to Sb and Sc and cover a factor of 10 in → metallicity. The total mass of the Local Group is estimated to be about 2 × 10¹² solar masses, although this value is still uncertain to within a factor of about 2. The velocities of the individual galaxies of the Local Group are not particularly high. Therefore no member is believed to be able to escape the group, which is thus considered to be gravitationally → bound. Another remarkable member of the Group is → IC 10.

→ local; → group.

The supercluster to which the Local Group belongs. It is composed of some 100 clusters of galaxies, with the Virgo cluster of galaxies at its center.

→ local; → supercluster.

Same as → Russell-Saunders coupling.

L referring to the total → orbital angular momentum and S to the total → spin angular momentum; → coupling.

The Wolf. A constellation in the southern hemisphere, located at about 15h right ascension, 45° south declination. Abbreviation: Lup; genitive: Lupi.

L. lupus "wolf," PIE *wlqwos/*lukwos; cf. Pers. gorg, as below; Gk. lykos; Albanian ulk; O.C.S. vluku; Rus. volcica; Lith. vilkas "wolf;" P.Gmc. *wulfaz (cf. O.S. wulf, O.N. ulfr, O.Fris., Du., O.H.G., Ger., E. wolf).

Gorg "wolf," Aftari dialect varg, M.Pers. gurg, O.Pers. Varkana- "Hyrcania," district southeast of the Caspian Sea, literally "wolf-land," today Iran Gorgân; Khotanese birgga-; Sogdian wyrky; Av. vəhrka-; Skt. vrka-.

Any of the several → dark clouds lying in the direction of the constellation → Lupus between → Galactic longitudes 334° < l < 352° and → Galactic latitudes +5° < b < +25°. In terms of angular extent the whole group is one of the largest low-mass star forming complexes on the sky, and it also contains one of the richest associations of → T Tauri stars. An average distance of about 150 pc places it among the nearest star forming regions, together with those in Corona Australis, Ophiuchus, Taurus-Auriga, and Chamaeleon (Comeron, 2008, in Handbook of Star Forming Regions Vol. II, PASP, Reipurth, ed.).

→ Lupus; → dark; → cloud.

An large nonthermal radio source in the constellation → Lupus, identified as a very old supernova remnant. It is also an extended source of soft X-rays.

→ Lupus; → loop.

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.

A young → stellar population that shares a common space motion. A moving group remains kinematically distinct within the general field stars at ages < 1 billion years, before being dispersed. As progenitor gas is cleared by OB star winds, and the natal cluster expands, stars with sufficiently high velocities become unbound and form a young, coeval moving group, possibly leaving behind a bound open cluster. Because of their common origin, moving group members have a shared age and composition. The nearest moving group is the → TW Hydrae association.

→ moving; → group.

A bright, blue star of V = 2.25 in the constellation → Puppis. It is a hot → supergiant of type O5, with a → surface temperature of 42,000 K, lying 1,400 → light-years away. Naos is one of the rarest → O-type stars visible to the → naked eye.

Naos, from Gk. naos "ship," since it used to be the Zeta star of Argo Navis (Jason's vessel Argos) before becoming Zeta in Puppis.

A theorem put forward by the 13th century Persian mathematician and astronomer Nasireddin Tusi to generate linear motion from a combination of circular motions, and thus improve the geocentric model of Ptolemy. A circle of radius R rotates inside a circle of radius 2R. The smaller circle rotates at twice the speed of the larger one and in opposite direction. The initial tangent point will travel in linear motion back and forth along the diameter of the larger circle. A particular case of → hypocycloid curves.

Named for Nasireddin Tusi (1201-1274), director of Marâgha observatory who created the Ilkhani zij; → couple.

The act of occupying; the state of being occupied.

Verbal noun of → occupy.

The energy level adopted by a particle, atom, or molecule under quantum mechanical laws.

Occupied, p.p. of → occupy; → level.

To take or fill up (space, time); to take possession and control of a place.

From O.Fr. occuper, from L. occupare "take over, seize, possess, occupy," from ob "over" + intensive form of capere "to grasp, seize, take;" PIE base *kap- "to grasp" (cf. Skt. kapati "two handfuls;" Gk. kaptein "to swallow," O.Ir. cacht "servant-girl," literally "captive;" Goth. haban "have, hold;" O.E. habban "to have, hold," probably Mod.Pers. qâp-, qâpidan "to seize;" Av. haf-, hap- "to keep, observe."

Hagidan, from dialectal Pers.: Šahmirzâdi hâgetan, Saraxsi hagiton, Tabari hâytan, haytan, Semnâni hâtan, Gilaki hâgitan, Lâsgardi agiton, degiton "to occupy;" maybe related to Av. haz- "to occupy;" Skt. sah- "to overcome, be victorious, prevail," saha- "victory," sahate "overcomes, masters;" Gk. ekhein "to have, hold;" PIE base *segh- "to have, to hold."

Eightfold; eight times as great.

L. octuplus, from octu- variant (before labials) of → oct- octa- + -plus "fold," from base of plicare "to fold, twist."

Haštâyi, from hašt "eight," → oct- octa- + -tâyi, from tâ "fold, plait, ply; piece, part," also a multiplicative suffix; Mid.Pers. tâg "piece, part."

A → multipole consisting of eight point charges. Octupole moments are much smaller than → quadrupole moments and very much smaller than → dipole moment.

→ oct-; → pole.

A bright star of → apparent visual magnitude  V = 4.3 lying in the constellation → Lupus. Among its other designations: HD 130807, HR 5528, HIP 72683. It is an → early-type star of → spectral type B5 IV and a member of the → Scorpius-Centaurus association. Ο Lupi is in fact a → binary system whose components have an angular separation of 0.043 arcsec, corresponding to a physical separation of 5.3 → astronomical units, with a mass ratio of 0.91.

→ Bayer designation; Lupi, genitive of → Lupus.

A group to which the speaker, the person spoken of, etc. does not belong.

→ out; → group.

Nâxodi, opposite of xodi "in-group," from nâ- "not," → un-, + xodi, → in-group.