Throughout the year, as Earth progresses through its orbit around the sun, one can witness stars in the night sky rise and set at different times. It's an example of an astronomical cycle visible to the naked eye, and the first of three subjects in Episode 3 of Crash Course Astronomy, a new series by Bad Astronomy's Phil Plait.

We're big fans of Plait's work and have so far been enjoying his collaboration with PBS Digital Studios. You can watch the first two installments on the Crash Course channel. Here's what Plait had to say about this week's episode:

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!


Good stuff. We'll be following this series closely.

[Bad Astronomy]