This week on Looking Up we learn the astronomical reason for the seasonal changes.
I have breaking news from the world of astronomy. The Earth has seasons! Ok, so maybe you already knew that. But do you know why? Ok, you probably do. You know that the Earth is tilted off being straight up and down in space by about 23 ½ degrees. But do you know why? Well, it’s because, we think, not too long after the Earth was formed, it got smacked by a massive collision with a protoplanet perhaps the size of Mars that knocked our fair planet off vertical and into, well, having seasons.
And there are astronomical markers for when our various seasons start and end. They don’t quite match up with the weather associated with a particular season – for example winter starts from an astronomical point of view only in December – but they are helpful astronomically. And this coming Sept. 22nd, we’ll plunge back in to astronomical Fall. On that day, the Sun appears to pass over the Earth’s equator, and you’ll see the Sun rise at exactly due east from everywhere on Earth, and sunset will be due west, also from anywhere on Earth. And so it is not surprising that ancient peoples kept track of these things, because they are excellent harbingers of the coming seasons on Earth. Knowing when to plant, when to harvest and such is very helpful for survival, and so knowing the movements of the Sun was very important. So, watch sunrise and sunset on the 22nd, and know that you are in tune with the ancient people who came before.
If you’d like to take a closer look at the Sun, or any of the other wonderful and amazing things in the sky, please visit csastro.org for a link to information on our monthly meetings and our free public star parties.