From the Glossary of Astronomical Terms by the Harvard-Smithsonian Center for Astrophysics: The Harvard-Smithsonian Center for Astrophysics (CfA) is located in Cambridge, Massachusetts. ...
Either of the two points (vernal, autumnal) on the celestial sphere where the ecliptic (which is the apparent path of the sun on the sky) intersects the celestial equator. Due to precession, this point moves over time, so positions of stars in catalogues and on atlases are usually referred to a "mean equator and equinox" of a specified standard epoch.
Note that epoch is often confused with equinox when applied to astronomical positions. In nearly all cases where epoch is used, equinox is what is really meant. Epoch simply means the date the observation was made. Equinox refers to the year when the center of right ascension meets the First Point of Aries, which is in the vernal equinox for the northern hemisphere of Earth. In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. ... A giant Hubble mosaic of the Crab Nebula, a supernova remnant. ... Equatorial Coordinates Right ascension (abbrev. ... The First Point of Aries, also called the vernal equinox point, is one of the two points on the celestial sphere where the celestial equator intersects the ecliptic. ... Illumination of Earth by Sun on the day of equinox The vernal equinox (or spring equinox) marks the beginning of astronomical spring. ... Earth (IPA: , often referred to as the Earth, Terra, the World or Planet Earth) is the third planet in the solar system in terms of distance from the Sun, and the fifth largest. ...
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