General astronomy

General astronomy

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General astronomy

reference star

Astronomy; General astronomy

A star whose position and/or proper motion are known and used as a local reference to define relative positions or proper motions of other stars in the same area of sky.

zone of avoidance

Astronomy; General astronomy

The area of the sky in which very few galaxies are visible. It is a result of obscuration by interstellar dust in the plane of the Milky Way, although the zone is actually inclined at 2° to the ...

astronomical unit (AU)

Astronomy; General astronomy

Approximately equal to the mean earth-sun distance, which is about 150,000,000 km or 93,000,000 miles. Formally, the AU is actually slightly less than the earth's mean distance from the sun ...

Any system for locating the positions of objects on the celestial sphere. Various systems are defined, according to the chosen point of observation (the origin) and the plane of reference they use. ...

distance modulus

Astronomy; General astronomy

The difference between the apparent magnitude of an object, m, corrected for *interstellar absorption, and its absolute magnitude, M. This difference is directly linked to the distance in parsecs, r, ...

luminosity class

Astronomy; General astronomy

A classification of stars according to their luminosity, which can vary widely for a given *spectral type. Luminosity class indicates, for example, whether a star is a supergiant, a giant, or a ...

asteroid

Astronomy; General astronomy

Any of the many small rocky or metallic objects in the Solar System, mostly lying in a zone (the asteroid belt) between the orbits of Mars and Jupiter; also known as a minor planet. They range in ...