By way of the astronomy picture of the day, I encountered a really fantastic site about the analemma.
The analemma is the apparent path that the sun takes in the sky during the year. If you record the
precise position of the sun at the same time every day, instead of being in exactly the same place
every day, it will traverse a figure eight, like in this image. This is an effect caused by a combination of the eccentricity of the earth's orbit, and the tilt of the earth's axis. It can be a bit hard to visualize just where the figure-eight shape comes from; the analemma site uses a combination of diagrams and animations to make it extremely clear, and works through the entire process of demonstrating where each component of the analemma comes from, and deriving the equations that describe it.
Kids: if you try this at home, be sure not to get thrown by Daylight Savings Time. Use a consistent clock.
And you can do the analemma thing with other objects, like the moon.
My favorite analema from APOD is this one:
http://antwrp.gsfc.nasa.gov/apod/ap030626.html
Search for 'analema' in APOD's search feature.