Spotting December New Moon as it Occults Mars Dec 11, 2010 10:21:08 GMT -6
Post by Centaur on Dec 11, 2010 10:21:08 GMT -6
Now explain it so a third grader can understand it! (and me!)
What I thought I saw on the software is this:
The Moon is plowing down toward the horizon and from SW toward S. The leading edge is a crescent. But even though the moon is apparently moving forward and down, stars (and a planet) behind it are being swallowed.
So this is my confusion, and I think Paulie's too originally. I would expect it to be catching up with stars instead of being caught. So thinking out loud, this means that the Earth (and thus the star) is spinning faster than the moon is rotating. However, if this is true, then it would seem that the moon would be moving in apparent retrograde motion, which it is not, at least compared to the horizon.
I also don't get how it could swallow objects from the trailing edge the first half of the month and the leading edge the second. I have thought about this with no successful conclusion for going on three days now and I keep getting stuck.
Patrick, study my diagram seen below. It is a permanent feature on my Moon webpage. When observed from above the Earth’s North Pole, the Moon orbits the Earth in a counterclockwise direction. Meanwhile, the Earth itself is rotating on its axis much faster in that same counterclockwise direction.
Notice the Moon when anywhere on the outer circle in the left half of the diagram. During that half month it is waxing and seems to be pulling away from the Sun. The dark (nighttime) side of the Moon appears to be leading.
Now notice the Moon when anywhere on the outer circle in the right half of the diagram. During that half month it is waning and seems to be heading toward from the Sun. The light (daytime) side of the Moon appears to be leading.
Now imagine a moment when as an observer at mid-northern latitude, you see that the Moon is transiting in the south. The Moon appears to be heading toward the right due to the Earth’s rotation. But due to its orbital motion around the Earth, the Moon appears to be moving toward the right more slowly than the stars surrounding it. In other words, relative to the stars it appears to be moving toward the left. This is the reason that stars appear to become immersed into the left side of the Moon when they are being occulted. They then appear to emerge from the right side of the Moon when the occultation concludes.