Vote 2020 graphic
Everything you need to know about and expect during
the most important election of our lifetimes

Check Out Crash Course Astronomy, A New YouTube Series From Phil Plait

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]

Share This Story

Get our newsletter



And he briefly touches on parallax shift, the effect that changes what stars we see in the sky during the year and also many, though not all of the, epicycles we see in planetary motion (To remove all the epicycles, we need elliptical not circular orbits, that had to wait for Kepler.).

And it's with parallax shift that we can tell how far away nearby stars are.* Combining this with the inverse square law we can determine a star's absolute brightness, this in turn leads to a lot other stuff, like guesses as to a star's temperature, the discovery of dust in the interstellar medium, etc, etc.

Combine this all with spectroscopes and telescopes and you pretty have the major tools of modern astronomy.

* The parallax shift is useless for very distant stars or other objects in the sky because the size of our planet's orbit is too small to cause any appreciable shift in the object's position in the sky.