![]() The subsolar point crosses the equator moving northward at the March equinox and southward at the September equinox. Note: The March equinox aka the vernal equinox marks the beginning of spring in the Northern Hemisphere and. the Sun is exactly overhead at a point on the equatorial line. It’ll happen at 3:07 UTC on Ma(10:07 p.m. Then the northern and southern hemispheres are equally illuminated.Įquinoxes are the only times when the subsolar point is on the equator, i.e. More specifically, the start of each season is marked by either a solstice (for winter and summer) or an equinox (for spring and autumn). The meaning of EQUINOX is either of the two points on the celestial sphere where the celestial equator intersects the ecliptic. The equinoxes are the only times when the solar terminator (the dividing line between night and day) is perpendicular to the equator. The March equinox marks the moment the Sun crosses the celestial equator – the imaginary line in the sky above the Earth’s equator – from south to north and vice versa in September. ![]() In 2023, the centre of the Sun crosses the celestial equator at 07:50 BST (06:50 UT) on 23 Septmber, the Northern Hemisphere autumn equinox. The word equilux is used to mean a day in which the durations of light and darkness are equal to distinguish the day from an equinox. Autumn equinox 2023: when it is and what it means. They are not exactly equal because of the angular size of the sun and atmospheric refraction. ![]() On an equinox, the Sun shines directly on the equator and the length of day and night is nearly equal – but not quite. CREDIT: NASA’s Earth Observatory Not Entirely Equal Day & Night On the September equinox, the terminator is a north-south line, and the sun is said to sit directly above the equator.
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