![]() The reason: The Gregorian calendar doesn't match up perfectly with the position of Earth in its orbit around the sun.Īs Earth orbits the sun, it revolves around its axis at a 23.5-degree angle so that it is pointed directly toward the sun at the summer solstice, directly away from the sun during the winter solstice, and at a right angle with the sun on the equinoxes that right angle means the sun shines about equal amounts of light across the Northern Hemisphere on the equinoxes. 23 but in 1931, the equinox happened on Sept. The autumnal equinox falls on different dates each year, usually Sept. The result? Dazzling light shows, with hues most commonly of pink, green, yellow, blue, violet and occasionally orange and white - depending on what elements the particles collide with. As the particles slam into Earth's magnetic field, they bump into atoms and molecules of oxygen, nitrogen and other elements. Particles that get discharged from the sun during such geomagnetic storms zip toward Earth at breakneck speed. That's because geomagnetic storms are about twice as frequent as the annual average during the fall. Besides the lengthening of nights and cool evening weather, which are great for stargazers, autumn truly is "aurora season," according to NASA. In addition to the brilliant colors of fall leaves, the autumn equinox signals another colorful spectacle - the aurora borealis, also called the Northern Lights. Here are five surprising facts about fall and the autumn equinox. ![]() The date of the fall equinox (and its spring counterpart) varies slightly each year, sometimes falling on the 23rd or 24th depending on the quirks of the calendar, along with Earth's slightly irregular orbit. ![]()
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