Most of the time, the angle of the Earth's rotation around its own axis, and that of its orbit around the Sun, vary from one another. However, as the Earth tilts backward and forward in its orbit, relative to the Sun, these two angles coincide from time to time. This event is known as an equinox, and happens twice a year, in March (the Vernal Equinox) and again in September (the Autumnal Equinox).
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