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Astronomy Terms

Astronomy terms are used to describe the various phenomena in space. In this section you can learn what every astronomy term means and how it helps us to better understand the cosmos.


Twilight, the light diffused over the sky from sunset to darkness and from darkness to sunrise.

Chronometer, a timepiece that is exceptionally accurate. Traditionally, the term refers to the marine chronometer, a rugged mechanical instrument used at sea to keep time for navigational purposes. See more »

Cosmogony, the study of the origin and development of the universe as a whole and of the individual bodies that compose it. See more »

Cosmology, the study of the universe. It is both a scientific subject and a philosophical one. See more »


Day, in astronomy, the average length of time between successive noons. Noon is defined as the instant when the sun is highest in the sky. See more »

Double Star, a pair of closely-spaced stars that to the unaided eye usually appear as a single star. See more »

Eclipse. An eclipse of the sun, or solar eclipse, occurs when the moon's shadow sweeps across the earth. See more »

Ecliptic, the apparent annual path of the sun among the stars. The sun appears to follow a path through the stars because the earth revolves around the sun. See more »

Epoch, in chronology (timekeeping), a point in time, such as 302 B.C. or October 30, 1936, or 7:34 A.M. See more »

Equinox, During the course of a year, the sun appears to move northward for about six months and southward for about six months. See more »

Evening Star, the name given to any of the five bright planets in the sky at sunset. See more »