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Today's the equinox, so why aren't sunrise and sunset the same?

Sept. 2, 2021, marks the autumnal equinox. Sept. 2, 2021, marks the autumnal equinox.
EDMONTON -

It's Wednesday, Sept. 22, the autumnal equinox. So, we should have 12 hours of daylight and 12 hours of darkness today, right?

Actually...no.

 

Sunrise in Edmonton today is at 7:20 a.m. and the sunset is at 7:31 p.m.

There's still 11 more minutes of daylight than night.

You have to wait until Saturday, Sept. 25, for that perfect 12/12 breakdown.

 

The equinox is the time when the midpoint of the sun is directly over the equator.

That'll happen at 1:21 p.m. today.

If we live near the equator, today would have twelve hours of both day and night.

But, the further away you are from the equator, the more of a difference there is between the equinox and the 12/12 split.

 

In autumn, the date for Edmonton's 12 hours of daylight and darkness is always a few days AFTER the actual equinox.

(And it's a few days BEFORE the vernal equinox.)

 

Here's why:

We're measuring three different points on the sun.

  1. Sunrise is the first sliver of sun on the horizon.
  2. Sunset is the last sliver.
  3. The equinox is the middle of the sun.

 

If the sun was a pinpoint, those different measuring points wouldn't matter much.

But, the sun is a rather large ball and there's a couple minutes of difference between those measuring points which throws things off.

There's also the fact that the atmosphere bends light and THAT also messes with the timing.

 

So, now you know. It's the equinox. But, for us, that DOESN'T mean equal day and night.  

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