Time in astronomy

thumb|Morning on a farm in [[Namibia, just after sunrise]] Morning is either the period from sunrise to noon, or the period from midnight to noon. In the first definition it is preceded by the twilight period of dawn, and there are no exact times for when morning begins (also true of evening and night) because it can vary according to one's latitude, and the hours of daytime at each time of year. However, morning strictly ends at noon, when afternoon starts.

thumb|Baku Street at Noon (1861) by Alexey Bogolyubov, depicting shadows from the sun at its highest point over the city of [[Baku]] Noon (also known as noontime or midday) is 12 o'clock in the daytime.

A solar equinox is a moment in time when the Sun appears directly above the equator, rather than to its north or south. On the day of the equinox, the Sun appears to rise directly east and set directly west. This occurs twice each year, around 20 March and 23 September.

A solstice is the time when the Sun reaches its most northerly or southerly excursion relative to the celestial equator on the celestial sphere. Two solstices occur annually, around 20–22 June and 20–22 December. In many countries, the seasons of the year are defined by reference to the solstices and the equinoxes.

time taken for a given object to make one complete orbit around another object, and applies in astronomy to mostly either planets or asteroids orbiting the Sun, moons orbiting planets, exoplanets orbiting other stars, or binary stars

thumb|Sunrise in Brisbane Water National Park, Australia thumb|A daytime sky with white clouds

period of time for the ecliptic longitude of the Sun to increase 360°

time standard

(of a celestial object) time that it takes to complete one revolution around its axis of rotation relative to the background stars

calculation of elapsed time by the apparent position of the sun

series of eclipses separated by a saros period

days since the beginning of the Julian Period

time standard based on the Earth's rotation

period of very close to 19 years that is nearly a common multiple of the solar year and the synodic (lunar) month

point on the celestial sphere

unit of time and a version of the year often used in astronomy

apparent solar time minus mean solar time

Rising of stars prior to sunrise

visual illustration of the history of the Universe

time standard

time standard for astronomical observations from the Earth

method of year numbering

return of a perturbed system into equilibrium

time of day in decimal units

form of solar time that corrects the variations of local apparent time, forming a uniform time scale at a specific longitude

position of the year within the 19-year Metonic cycle

intervals of eclipses

theoretical description of motion of Earth's moon

advanced astronomical clock

An exeligmos () is a period of 54 years, 33 days that can be used to predict successive eclipses with similar properties and location. For a solar eclipse, after every exeligmos a solar eclipse of similar characteristics will occur in a location close to the eclipse before it. For a lunar eclipse the same part of the earth will view an eclipse that is very similar to the one that occurred one exeligmos before it (see main text for visual examples). The exeligmos is an eclipse cycle that is a triple saros, three saroses (or saroi) long, with the advantage that it has nearly an integer number of

Calculations pertaining to orbits

Period when eclipses can occur

Method of determining the age of events or artifacts

time standard

time standard used in astronomy

In astronomy, an octaeteris (, plural: octaeterides) is the period of eight solar years after which the moon phase occurs on the same day of the year plus one or two days.

astronomical cycle he created

Hebrew term ascribed to an hour of a 12-hour day and how it is to be reckoned

Analogy to communicate geologic time

equation to derive time of sunset and sunrise