- Before Christ (B.C.) 代表纪元前，Anno Domini (A.D.) 代表纪元后。
- 联合国采用公元Before the Common Era (B.C.E.) 和 Common Era (C.E.)
- 公元525年，基督教神学家狄奥尼修斯·伊希格斯建议将耶稣生年定为纪元元年，以取代当时罗马教廷所采用的“戴克里先历”
Equator
Ecliptic
Equinox
A solar equinox is a moment in time when the Sun crosses the Earth’s equator, which is to say, appears directly above the equator, rather than north or south of the equator.
- 3月20日
- 9月23日
Solstice
A solstice is an event that occurs when the Sun appears to reach its most northerly or southerly excursion relative to the celestial equator on the celestial sphere.
- 6月21日
- 12月22日