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This article is about the time interval used in astronomy. For years in the Julian calendar, see Julian calendar. Julian year - a unit of time defined as exactly 365.25 days light year - the distance light travels in a vacuum in a period of 1 Julian year; a unit of distance equal to about 5.9 trillion miles (9.5 trillion kilometers) ... .
Animation showing the difference between a sidereal day and a solar day. Sidereal time ("sidereal" pronounced / saɪˈdɪəriəl, sə -/ sy-DEER-ee-əl, sə-) is a system of timekeeping used especially by astronomers. Using sidereal time and the celestial coordinate system, it is easy to locate the positions of celestial objects in the night sky.
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Julian Date. The number of days since noon on January 1, -4712, i.e., January 1, 4713 BC (Seidelmann 1992). It was proposed by J. J. Scaliger in 1583, so the name for this system derived from Julius Scaliger, not Julius Caesar. Scaliger defined Day One was as a day when three calendrical cycles converged.
The saros ( / ˈsɛərɒs / ⓘ) is a period of exactly 223 synodic months, approximately 6585.321 days, or 18 years, 10, 11, or 12 days (depending on the number of leap years ), and 8 hours, that can be used to predict eclipses of the Sun and Moon. One saros period after an eclipse, the Sun, Earth, and Moon return to approximately the same ...
Barycentric Dynamical Time ( TDB, from the French Temps Dynamique Barycentrique) is a relativistic coordinate time scale, intended for astronomical use as a time standard to take account of time dilation [1] when calculating orbits and astronomical ephemerides of planets, asteroids, comets and interplanetary spacecraft in the Solar System.
21. 14:14. 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. On the day of the equinox, the Sun appears to rise "due east" and set "due west". This occurs twice each year, around 20 March and 23 September.
