Equinoxes, seasons, and why daylight is shrinking so rapidly


Again with the moon and sun and planets stuff you say? Yes, it’s that time again. Why? Because space is rad, and also because I had a thought the other day that if the kids asked me why the daylight is shrinking so rapidly right now or what causes the seasons to change I didn’t really have a great answer.

Thanks to NASA, I now have a better one. 😉

Here are some things I re-learned and just never knew that surprised me about what causes the seasons.

  1. The earth is tilted on it’s axis (ok, I knew that) and that, along with the earth’s annual orbit around the sun, is what causes the seasons to change. It has nothing to do with how close or far away to the sun though, which might have got me if I was on Who Wants To Be A Millionaire honestly.
  2. The solstices, winter and summer, occur when the north pole is pointed away from the sun or when the south pole is pointed away from the sun respectively (or vice versa depending on your hemisphere).
  3. The equinoxes (fall and spring) occur when both poles have an “equal” view of the sun.
  4. During the equinoxes, everywhere on earth has the same amount of daylight (~12 hours)! After that, one-half of the earth is going to see rapidly decreasing daylight (heading into winter) and the other rapidly increasing daylight (heading into summer). At least if you don’t live right on the equator that is.

Since we just passed the fall equinox (on September 22nd), and I’m in the northern hemisphere (quite far north I might add), our days are rapidly getting shorter now.

The way I visualize this happening is by imagining the earth is like a car. During the solstices (summer and winter) we are looking at the sun through the front windshield or rear window of our car. During the equinoxes (fall and spring) we are looking at the sun as if passing it (or vice versa). When you pass something in a car, the object goes by quick, and the changing daylight in the spring and fall is the same. Fast.

Alternatively, when you are approaching or going away from an object in a car, it tends to stay in view for a long time and change more slowly, just like how there are long stretches in winter and summer where the daylight doesn’t change very much.

This graphic from NASA shows it nicely: when the earth is at each side it’s summer and winter, and when it is “passing” the sun, it’s fall and spring

I feel much more prepared now for the “why are their seasons” question now, should it ever be asked. What a relief. 😉

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One response

  1. That picture with the sun and earth is perfect for me. I didn’t fully understand those seasons myself before. It all makes sense now!

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