Of course, Earth never stops moving around the sun. The sun is overhead at noon as seen from the equator. Earth’s two hemispheres are receiving the sun’s rays about equally around equinox time. We have an equinox twice a year – spring and fall – when the tilt of the Earth’s axis and Earth’s orbit around the sun combine in such a way that the axis is inclined neither away from nor toward the sun. And that means Earth’s Northern and Southern Hemispheres trade places throughout the year in receiving the sun’s light and warmth most directly. It’s caused by Earth’s tilt on its axis and ceaseless orbit around the sun. Today, we know each equinox and solstice is an astronomical event. They could easily see that the sun’s path across the sky, the length of daylight, and the location of the sunrise and sunset all shift in a regular way throughout the year. They used the sky as both a clock and a calendar. The earliest humans spent more time outside than we do. Two factors cause more day than night at an equinox. But that doesn’t mean that day and night are exactly equal in length. Read: Why aren’t day and night exactly equal on the equinox? Around the time of an equinox, Earth’s Northern and Southern Hemispheres are receiving the sun’s rays equally. The name equinox comes from the Latin aequus (equal) and nox (night). For everyone across the globe, days and nights are approximately equal in length. Note: On this equinox, the sun crosses above Earth’s equator, moving from north to south. CDT on September 22 for central North America translate UTC to your time). When is the next one? The next September equinox will fall at 1:04 UTC Septem(8:04 p.m. What is it? The September equinox marks the sun’s crossing above Earth’s equator, moving from north to south. Meanwhile, south of the equator, spring begins. Read more about these images, which are via NASA Earth Observatory.įor us in the Northern Hemisphere, the sun is rising later now, and nightfall comes sooner. From left to right, a June solstice, a September equinox, a December solstice, a March equinox. With each passing day, the sun will rise slightly more south until the Winter Solstice occurs on 21 December this year.Satellite views of Earth on the solstices and equinoxes. The Celestial Equator is the celestial analog of the Earth’s equator projected onto the sky and thus, we define and derive the Cardinal Directions (N, E, S, W) from the equator. On this day, and likewise on the Vernal Equinox, the sun crosses the celestial equator with equal hours of daylight and darkness, 12 hours each, it will rise due east and set due west. Local noon is defined as the transit of the sun across the meridian. Note in the image below, the location of the sun and the meridian and that the Equinox occurs east (2h, 24m) of local noon for locations along the North American Eastern seaboard.
Yesterday the sun transited the celestial equator (Declination: 0º, Right Ascention: 12h:00m), midway between the solstices (Summer, in June and Winter, in December). This is the second time this year, and every year, that marks the date and time when there are equal hours of daylight and darkness, the first being the Vernal Equinox, the Astronomical beginning of Spring. At 14:21 UTC (10:21 EDT) yesterday, the Autumnal Equinox occured, the Astronomical beginning of Autumn.
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