Storm Team Academy: Do we have equal amount of day and night on the equinoxes?

Storm Team Academy

Do you we have equal amounts of day and night when it’s the equinox?

The answer is…. not quite.

Sunrise on the fall equinox this past Tuesday was 6:52 am, and the sunset was 7:01pm. That equals to 12 hours and 8 minutes of daylight. It’s close to an even 12-hour split, but not quite equal.

Why is that? Two reasons:
1) The sun is a disk and not a point.
2) Atmospheric refraction.

The sun appears in the sky as a disk, it doesn’t come to a point. The official sunrise is when the topmost part of the sun first first touches the eastern horizon. And a sunset is when the topmost part of the sun disappears below the western horizon. This adds about an extra 2 1/2 to 3 minutes of daylight at the mid latitudes, which is central New York is located.

The other reason is atmospheric refraction. Think of the atmosphere like a lens or a prism. When sunlight passes through the atmosphere it makes the sun appear to be a half degree from its true position when it’s near the horizon. This is makes the sunrise time seem earlier and the sunset a little later. It adds about another six minutes of daylight!

6ish minutes+2ish minutes = 8 ish minutes.

So that’s why the amount of daylight on the equinox was off by more than 8 minutes!

We have much more information on the seasons and fun facts about when the daylight does balance out on the vernal and autumn equinoxes if you click here.

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