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SYFY WIRE Bad Astronomy

Crash Course Astronomy Episode 3: Cycles in the Sky

By Phil Plait

You live on a whirling ball of rock and metal. As it spins it also revolves around the Sun, and all this is set in a backdrop of thousands of visible but much more distant stars … and on top of that, there are other planets in the solar system moving around as well.

What does all this look like? Why, that’s the very topic of Episode 3 of Crash Course Astronomy: Cycles in the Sky.

When I sat down to write the syllabus (and later the scripts) for this series, the topic of motions in the sky was one I approached with a bit of trepidation. It’s not easy for most folks to picture how all this works; it can be hard to visualize what’s going on, especially when you’re changing your viewpoint from what’s physically happening (the Earth is spinning, the Earth is tilted, the Earth is moving around the Sun) to what you’re seeing from the Earth (stars rise and set, some stars are forever below the horizon from your latitude, stars change their position over the year).

I hope this episode makes this a little bit easier to understand. If it’s still hard to grasp some of this, that’s OK! It’s always hard at first; it was hard for me. I’ve been doing this a long time now though, so I have a lot of experience going outside and seeing how all these celestial gears fit together. It’s actually a fascinating feeling, looking up and knowing that everything is in motion, and it’s all working under the rules of gravity, momentum, geometry … things we can understand and predict. All the parts are working!

And you can be a part of this too. Go outside and look up. And not just tonight, but tomorrow, and the next night, and the next. Keep looking up. Get to know the night sky, its starry denizens, and its motions. It really is an amazing experience.

Wanna watch more Crash Course Astronomy? The playlist is on YouTube.

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