Chapter 1

Powers of ten animation: This is a classic animation showing the difference between sizes. It helps grasp the scale of objects - how big is 1,000,000 meters? How big is one meter for that matter? Here is a parody of this famous video on the Simpsons show

Movie of the shadow over a day: I made this myself (you may want to skim through it - or it takes too long)

Stellarium: This free, open-source software is a sky simulator. Basically, you can enter a location on Earth and a time (and year), and it will show you what the sky looks like. This is great because you can do things you can't do in real life - like watch the sky over the course of a month (well, you can do that, but it takes a month). This software runs in Linux, Windows, and Mac OS X.

Images of Phases of the Moon: These are real images of the Moon over the course of a month. Notice how the image "woobles" - this is a real effect due to the non-constant speed at which it goes around the Earth (more on this later)

Relative Size of Earth-Moon: You may be surprised. Most people have a distorted image of the size-distance relation between the Earth-Moon.

Phases of the Moon Applet: I highly recommend this one.

Another phases of the Moon: Drag the moon around the Earth and then click "view from the Earth" and it will show you what it would look like.

This first animation shows why one would think there should be a solar eclipse every month. (click play). The next animation starts off in a similar view, but shows why eclipses are actually rare.

Kepler Applet: This applet can show two things really well. First, for the elliptical orbit, notice that the speed of the object increases when it is closer to the Sun. Second, if you click the "sweep" button, it will sweep out areas for same time intervals.

Another Kepler Applet: This one is fun to play with. Click and drag to place a planet and the dragging gives it a speed and direction. When you let go, it will show its motion. If you click "show kepler's law", it will show the equal areas in equal times.

Parallax Demo: Remember that the discussion between heliocentric and geocentric models had a lot to do with the lack of detectable stellar parallax. This demo shows what parallax is. After you click the link, scroll down to the applet for parallax.

Here is a "sun tracker" - simply enter month and day and location and it will show you the motion of the Sun for that day. It is difficult to determine the highest point of the sun (if it is overhead or not) and it does not show the exact direction that the sun rises and sets, but it is still useful.