![]() ![]() ![]() Atmospheric refraction describes the way light seems to bend or deviate from a straight line as it passes through Earth’s atmosphere. This is largely due to atmospheric refraction. (The solar terminator is the shadowed line indicating daylight and sunlight on a globe.) A true equinox would indicate 12 hours of both day and night.Īlthough the equinoxes are as close to this phenomenon as happens on Earth, even during the equinoxes day and night aren’t exactly equal. This is the December solstice.Īs its name suggests, an equinox indicates equally illuminated hemispheres, with the solar terminator equally dividing Earth from north to south. Around December 21, the subsolar point hits the Tropic of Capricorn (23.5°S). After the September equinox, the subsolar point continues to move south as the Southern Hemisphere tilts toward the sun. This is the June solstice, after which the subsolar point begins to migrate south. Around June 21, the subsolar point hits the Tropic of Cancer, (23.5°N). After the March equinox, the subsolar point migrates north as the Northern Hemisphere tilts toward the sun. Only during an equinox is Earth's 23.5° axis not tilting toward or away from the sun: the perceived center of the Sun’s disk is in the same plane as the Equator.īefore and after the equinox, the subsolar point migrates north or south. The subsolar point is an area where the sun's rays shine perpendicular to Earth's surface-a right angle. (The Equator, of course, is 0° latitude.) So, equinoxes are the only times of the year when the subsolar point is directly on the Equator. ![]() Solar declination describes the latitude of Earth where the sun is directly overhead at noon. The September equinox is the autumnal equinox in the Northern Hemisphere and the vernal in the Southern.ĭuring the equinoxes, solar declination is 0°. The March equinox is the vernal equinox in the Northern Hemisphere, and the autumnal equinox in the Southern. On Earth, there are two equinoxes every year: one around March 21 and another around September 22. Sometimes, the equinoxes are nicknamed the “ vernal equinox” (spring equinox) and the “ autumnal equinox” (fall equinox), although these have different dates in the Northern and Southern Hemispheres. The equinoxes are the only time when both the Northern and Southern Hemispheres experience roughly equal amounts of daytime and nighttime. The spring will last until the summer solstice, which occurs on June 20 or June 21 in the Northern Hemisphere and December 21 or December 22 in the Southern Hemisphere.An equinox is an event in which a planet’s subsolar point passes through its Equator. The vernal equinox happens in the Northern Hemisphere around March 20 or March 21, whereas in the Southern Hemisphere is occurs around September 22 or September 23. Over the next three months, the sun will move higher and higher in the sky, resulting in longer periods of daylight. The word "equinox", literally means "equal night", as it derives from the Latin "aequus" (equal) and "nox" (night). In this case, the Earth's axis isn't tilted towards or away from the sun, meaning there are 12 hours of daylight and 12 hours of darkness all over the planet. The vernal equinox happens when the Earth's axis reaches a particular position and the centre of the sun is directly above the Equator, meaning that both day and night are of approximately equal length. Spring 2022 has finally arrived, and will be marked by the vernal equinox, which takes place on this Sunday, March 20. ![]()
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