The Sun's Position on the Celestial Sphere

[Play/Download Movie (6 MB)]

I usually start talking about the Celestial Sphere by giving a colloquial description of three dimensional polar coordinates (without telling the students that that's what I'm doing, as that terminology would cause them all to switch off). to locate a star on the sky, you only need to know two angles. (I describe azimuth and altitude, again without the names, since they are easier to demonstrate sitting on the Earth, but the important thing is the principle.) To just see where it is, you don't have to know how far away it is. I use this to justify pretending that stars are all on a celestial sphere for purposes of predicting where we'll see them.

The purpose of this animation is to show how, given that the Earth is orbiting the Sun, the Sun appears to move over the course of the year around the celestial sphere. It stars by showing the Earth orbiting the Sun embedded in the celestial sphere. It zooms in to show where the Sun appears to be to an Earthbound observer on the equinoxes and the solstices.

As with many of my movies, there is no narration or sound. It's designed to be used by a lecturer, who will pause it at opportune places to discuss it or ask questions of students.

This work is licensed under a Creative Commons License.

Earth texture by Rick Kohrs.

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