Re: As I stand and watch, which goes overhead faster? The Sun or the Moon?

Dear Peter,

 Well asking me not to mention Galileo or the heliocentric "hypothesis" (it's not a hypothesis, the Earth does go around the Sun) would make it impossible to answer the question. The Moon appears to move more rapidly across the sky. I say appears because the motion of both the Moon and the Sun is due mainly to the Earth's rotation.

To see why the Moon appears to move more quickly we have to make an approximation. Namely, neither the Earth going around the Sun or the Moon going around the Earth follow circular paths. They move along ellipses. However, these ellipses are almost nearly circles, so we will assume that they are circles.

It takes the Moon approximately 27.3 days to go around the Earth. If we assume the orbit is a perfect circle we can just divide the circle's 360 degrees by 27.3 days and get a motion of about 13.2 degrees per day or about 6.6 degrees for an average 12 hour night. (Remember the length of night changes continuously during the year because of the change of the Earth's speed as it moves around the Sun and because of the tilt of the axis. When the Earth is closer to the Sun it moves more rapidly than when it is farthest from the Sun.) What this means is that if the Moon rises at sunset at six pm, after 12 hours it will appear to have moved 186.6 degrees through the sky---180 degrees from rise to set plus the 6.6 degrees from its own motion. (Of course, as we can see only 180 degrees of the sky at any given time [even less due to buildings, trees, light pollution, etc.], what our calculation really shows is that the Moon would take less than 12 hours to move 180 degrees across the sky.)

 Now let's look at the motion of the Sun on a similar 12 hour day. It takes the Earth approximately 365.25 days to go around the Sun. If we again assume a circular orbit, 360 degrees divided by 365.25 days we get a motion of about 1 degree per day. The Sun will appear to move 181 degrees between sunrise and 12 hours later.

Conclusion the Moon moves faster.

 I don't think it would be particularly obvious to a casual observer that the Moon seems to move faster. It's hard to compare their motions. If you watch the Moon over a period of several hours you can see it move against the background of stars. Determining the Sun's motion is more difficult because there are no stars visible during the day. However, with careful observations during twilight, it is possible to determine the Sun's motion. Indeed, the accumulated observations of astronomers long before Galileo provided the evidence to show this.

 Hope this helps,
Mike Francis
http://www.gis.net/~mtf/sm.htm

 Follow my link and you'll see why I couldn't resist mentioning Galileo.