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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. 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.
The March equinox is known as the vernal equinox (spring equinox) in the Northern Hemisphere and as the autumnal equinox (autumn equinox or fall equinox) in the Southern Hemisphere. [ 8 ][ 7 ][ 10 ] On the Gregorian calendar, the northward equinox can occur as early as 19 March or as late as 21 March at 0° longitude.
The September equinox (or southward equinox) is the moment when the Sun appears to cross the celestial equator, heading southward. Because of differences between the calendar year and the tropical year, the September equinox may occur from September 21 to 24. At the equinox, the Sun as viewed from the equator rises due east and sets due west.
17:37. 21. 14:14. 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.
Gregorian calendar. The Gregorian calendar is the calendar used in most parts of the world. [1][a] It went into effect in October 1582 following the papal bull Inter gravissimas issued by Pope Gregory XIII, which introduced it as a modification of, and replacement for, the Julian calendar. The principal change was to space leap years ...
The December-solstice solar year is the solar year based on the December solstice. It is thus the length of time between adjacent December solstices. The length of the December-solstice year has been relatively stable between 6000 BC and AD 2000, in the range of 49 minutes 30 seconds to 50 minutes in excess of 365 days 5 hours.
Equinox (celestial coordinates) In astronomy, an equinox is either of two places on the celestial sphere at which the ecliptic intersects the celestial equator. [1][2][3] Although there are two such intersections, the equinox associated with the Sun 's ascending node is used as the conventional origin of celestial coordinate systems and ...
14:14. Earth during the summer solstice in June 2017. The summer solstice or estival solstice[i] occurs when one of Earth 's poles has its maximum tilt toward the Sun. It happens twice yearly, once in each hemisphere (Northern and Southern). For that hemisphere, the summer solstice is the day with the longest period of daylight and shortest ...