An Etymological Dictionary of Astronomy and Astrophysics
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The point on the → celestial horizon 90° → clockwise from the → north point. The point where the Sun rises at the → equinoxes.

O.E. east, from P.Gmc. *aus-to-, *austra- "east, toward the sunrise" (cf. Du. oost, Ger. Ost, O.N. austr "from the east"), from PIE *aus- "dawn" (cf. Av. uš-, ušah- "dawn," Skt. usas-, usah- "dawn," Gk. aurion "morning," Lith. auszra "dawn," L. aurora "dawn," auster "south").

Xâvar "east," originally "west," from Mid.Pers. *xvar barân "where the Sun is led," from xvar "sun" (Av. hū-, hvar- "sun", cf. Skt. surya-, Gk. helios, L. sol, O.H.G. sunna, Ger. Sonne, E. sun; PIE base *sawel- "sun") + barân, pr.p. of bar-, bordan "to carry, lead" (Mid.Pers. burdan, O.Pers./Av. bar- "to bear, carry," barəθre "to bear (infinitive)," Skt. bharati "he carries," Gk. pherein, L. fero "to carry;" PIE base *bher- "to carry") + time and place suffix -ân.

Lying toward or situated in the east.

From → east + -ern an adjective suffix occurring with names of directions.

Xâvari from xâvar, → east, + -i adj. suffix.

The position of a planet when it can be seen in the western sky just after sunset.

→ eastern; → elongation.

The Greatest → elongation of an inferior planet occurring after sunset.

Superlative of → great; → eastern; → elongation.

Smallest in size, amount, degree, etc.

From M.E. leest(e), O.E. læst, læsest "smallest" (superlative of læs "smaller, less").

Kucaktarin, kamtarin, superlatives of kucak and kam, → small.

Of two or more → integers, the smallest positive number that is divisible by those integers without a remainder.

→ least; → common; → multiplier.

Any statistical procedure that involves minimizing the sum of squared differences.

→ least; → square.

A → cross correlation technique for computing average profiles from thousands of → spectral lines simultaneously. The technique, first introduced by Donati et al. (1997, MNRAS 291,658), is based on several assumptions: additive → line profiles, wavelength independent → limb darkening, self-similar local profile shape, and weak → magnetic fields. Thus, unpolarized/polarized stellar spectra can indeed be seen as a line pattern → convolved with an average line profile. In this context, extracting this average line profile amounts to a linear → deconvolution problem. The method treats it as a matrix problem and look for the → least squares solution. In practice, LSD is very similar to most other cross-correlation techniques, though slightly more sophisticated in the sense that it cleans the cross-correlation profile from the autocorrelation profile of the line pattern. The technique is used to investigate the physical processes that take place in stellar atmospheres and that affect all spectral line profiles in a similar way. This includes the study of line profile variations (LPV) caused by orbital motion of the star and/or stellar surface inhomogeneities, for example. However, its widest application nowadays is the detection of weak magnetic fields in stars over the entire → H-R diagram based on → Stokes parameter V (→ circular polarization) observations (see also Tkachenko et al., 2013, A&A 560, A37 and references therein).

→ least; → square; → deconvolution.

A fit through data points using least squares.

→ least squares; → fit.

A method of fitting a curve to data points so as to minimize the sum of the squares of the distances of the points from the curve.

→ method; → least squares.

The principle that, for a system whose total mechanical energy is conserved, the path to be taken for the system from one configuration to another is the one whose action has the least value relative to all other possible paths and from the same configurations. Also called Maupertuis' principle, least-action principle.

→ principle; → least; → action.