Celestial horizon, one axis of the altazimuth coordinate system. It is the great circle on the celestial sphere midway between the observer's zenith and nadir; it divides the celestial sphere into two equal hemispheres. The observer may be unable to see all the stars that lie above his celestial horizon because of obstructions such as buildings, trees, or mountains; he may be able to see some stars that lie below his celestial horizon because of atmospheric refraction.
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The distance between the sun and the earth varies because the earth travels in an elliptical rather than circular orbit. The distance is r... -
Galaxy, a massive ensemble of hundreds of millions of stars, all gravitationally interacting, and orbiting about a common center. Astronomer... -
Ecliptic, in astronomy, the apparent great-circle annual path of the sun in the celestial sphere , as seen from the earth . It is so named b...