DECATUR, Ill. (WAND) - The Autumnal Equinox, the time of year when the sun is directly over the equator, occurred at 1:19 p.m. today. Equinox, by definition, is equal parts day and night.
So, one would believe that we had 12 hours of sun and 12 hours of darkness today. But that really is not true. While sunrise and sunset will vary slightly based on your location, it was generally sun up at 6:43 a.m. and sun down at 6:52 p.m. The reason daylight is longer than 12 hours is twofold.Â
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First, there is atmospheric refraction. The Earth's atmosphere bends, or refracts, sunlight, causing the Sun to appear slightly above the horizon even when it is actually just below it. This effect makes the Sun visible for a longer period during sunrise and sunset, leading to a longer duration of daylight than the actual geometric day length.
Next, there is the definition of sunrise and sunset. The official times for sunrise and sunset are typically measured when the upper edge of the Sun's disk touches the horizon, not its center. Because the Sun is a disk, this means that sunrise occurs slightly before the Sun's center is on the horizon, and sunset occurs slightly after, slightly extending the duration of daylight.Â
While we do not have issues with mountains, local topography in other parts of the world can also play a role in sunrise/sunset times.  Â
So, with this knowledge in hand, who is ready to rename the start of Fall to the Autumnal Quasi-Equinox? Anyone? Anyone? Â
Well, some cooler weather is headed back to Central Illinois, albeit short-lived. So, stay safe, stay weather-aware and stay sweaty.Â
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