Looking at the moon

[Forealfc]

Okay... I know I know... this is probably like a Duh question for some of you.. but oh well.. Im still going to ask....

The other night I was looking at the moon.. and I was just wondering how is it that we on Earth are spinning so fast that the moon stays intact? I'm totally confused? I mean, does the moon spin along with us as well? When I was looking at the moon, it seemed to be in the same place practically the whole night...


Oh one more questions? The astronauts in space right now on the ISS.. ... Are they turning fast as well?? Do they even feel it when doing spacewalks?

[John L]

Well, the Earth rotates on its axis at about 1,000 mph (approx 24,000 mile circumference and a 24 hour day), while the Moon rotates on its axis at about 10 mph (approx 6,800 mile circumference and a 28 Earth-Day day). The Earth orbits the Sun at about 67,000 mph (approx 584,000,000 trip around the sun at 365 days), while the Moon orbits the Earth at about 1,100 mph (approx 750,000 miles trip around the Earth at 28 Earth days). As for astronauts it depends on their orbit, but a 17,000 mph orbital speed is a common approximate speed, such as the guys on the ISS right now. They make a complete orbit of the Earth about every 90 minutes.

Now the Moon will actually rise and set just like the stars, but will move quite a bit in relation to the background stars during the night. Just after sunset, look at the Moon and try to identify what constellation it is in and what bright stars in that constellation are near the leading and trailing sides of the Moon. Just before sunrise, or before the Moon sets, compare what you saw at sunset and what you see at sunrise and you'll be able to see that the Moon did move relative to the background stars. Over the 28 day month you'll see that the Moon makes a complete trip around the Earth and through the various constellations along it's apparant path.

As to why the Moon isn't torn apart, that's because the Moon is only a gravitationally bound body to the Earth, and both the Earth and the Moon are held together by their own respective gravity. The speed of the Earth's and the Moon's spin are only affected by the gravitational pull of the two bodies. Over time, the drag created by the Moon's gravity on the Earth will slow down the Earth's spin and make our days longer. At the same time the Moon's spin will slow down along with the Earth's. You may have noticed that the Moon always shows the same face to the Earth, only appearing different because of the angle of sunlight reaching the surface facing us. Over time, the slow down that the Earth and Moon cause each other will make the Earth slow down until it only ever shows the same face to the Moon, but the Moon will slow down at a rate to continue to always show the same face to the Earth. Incidentally, as all this slowing down is going on, the Moon will slowly drift away from the Earth - never escaping, but maintaining the spin and orbit size necessary to keep the same face towards the Earth while still slowing down. This is called RESONANCE.

Pluto and its Moon are Doubly Resonant. Pluto's day is 6.38 Earth days, Charon's (Pluto's Moon) day is 6.38 Earth days, and Charon's Month (one orbit around Pluto) is 6.38 Earth days. This means that Charon is always directly above the exact same spot on Pluto (if you were on the opposite side of Pluto you would never see Charon) and they both always show the exact same face to each other. One day, the Earth and Moon may form the same doubly resonant pattern, but that will be an extremely long time in the future.

[foreal]

Bravo!!! Thanks so much John L