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

Unusual or considerable in degree, power, intensity, number, etc.

O.E. great "big, coarse, stout," from W.Gmc. *grautaz (cf. Du. groot, Ger. groß "great").

Bozorg "great, large, immense, grand, magnificient;" Mid.Pers. vazurg "great, big, high, lofty;" O.Pers. vazarka- "great;" Av. vazra- "club, mace" (Mod.Pers. gorz "mace"); cf. Skt. vájra- "(Indra's) thunderbolt," vaja- "strength, speed;" L. vigere "be lively, thrive," velox "fast, lively," vegere "to enliven," vigil "watchful, awake;" P.Gmc. *waken (Du. waken; O.H.G. wahhen; Ger. wachen "to be awake;" E. wake); PIE base *weg- "to be strong, be lively."

A hypothesized large concentration of mass (about 10¹⁶  → solar masses), some hundred million → light-years from Earth, in the direction of the → Centaurus → supercluster, that seems to be affecting the motions of many nearby galaxies by virtue of its gravity.

→ great; → attractor.

A circle on a sphere whose plane passes through the center of the sphere.

→ great; → circle.

One of a series of dark spots on → Neptune similar in appearance to Jupiter's → Great Red Spot. It was discovered in 1989 by NASA's Voyager 2 space probe. Also known as GDS-89. The dark, oval spot had initial dimensions of 13,000 × 6,600 km, about the same size as Earth. Although it appears similar to Jupiter's spot, which is an → anticyclonic storm, it is believed that the Great Dark Spot is an atmospheric hole similar to the hole in Earth's → ozone layer ozone layer. Moreover, unlike Jupiter's spot, which has lasted for hundreds of years, the lifetimes of Great Dark Spots appear to be much shorter, forming and disappearing once every few years or so. Based on pictures taken by Voyager and since then with the → Hubble Space Telescope, Neptune appears to spend somewhat more than half its time with a Great Dark Spot. Around the Great Dark Spot, winds were measured blowing up to 2,400 km an hour, the fastest in the solar system.

→ great; → dark; → spot.

An anticyclonic storm on the planet Jupiter akin to a hurricane on Earth, but it is enormous (three Earths would fit within its boundaries) and it has persisted for at least the 400 years that humans have observed it through telescopes.

→ great; → red; → spot.

An apparent fissure in the bright clouds of the Milky Way between → Cygnus and → Sagittarius caused by a series of large, dark, overlapping clouds.

→ great; → rift.

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

Superlative of → great; → eastern; → elongation.

The instant when the axis of the Moon's → shadow cone passes closest to Earth's center. For → total eclipses, the instant of greatest eclipse is virtually identical to the instants of greatest magnitude and greatest duration. However, for → annular eclipses, the instant of greatest duration may occur at either the time of greatest eclipse or near the sunrise and sunset points of the eclipse path (F. Espenak, NASA).

Superlative of → great; → eclipse.

The largest → elongation of an inferior planet from the Sun. It may be → greatest eastern elongation or → greatest western elongation. The greatest elongation of Mercury is about 28°, and thus Mercury can only be observed 112 minutes after sunset or before sunrise. For Venus, it is about 47°, making it visible at most about 3 hours after sunset or before sunrise.

Superlative of → great; → eastern; → elongation.

The Greatest → elongation of an inferior planet occurring before sunrise.

Superlative of → great; → western; → elongation.