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Top Document: [sci.astro] Solar System (Astronomy Frequently Asked Questions) (5/9) Previous Document: E.14 Earth-Moon system Next Document: E.14.2 Why does the Moon always show the same face to the Earth? See reader questions & answers on this topic! - Help others by sharing your knowledge In fact the Moon *does* rotate: It rotates exactly once for every orbit it makes about the Earth. The fact that the Moon is rotating may seem counterintuitive: If it's always facing towards us, how can it be rotating at all? To see how this works, put two coins on a table, a large one to represent the Earth, and a small one to represent the Moon. Choose a particular place on the edge of the "Moon" as a reference point. Now, move the Moon around the Earth in a circle, but be careful to always keep the spot you picked pointed at the Earth (this is analogous to the Moon always keeping the same face pointed at the Earth). You should notice that as you do this, you have to slowly rotate the Moon as it circles the Earth. By the time the Moon coin goes once around the Earth coin, you should have had to rotate the Moon exactly once. This exact equality between the Moon's rotation period and orbital period is sometimes seen as a fantastic coincidence, but, in fact, there is a physical process which slowly changes the rotation period until it matches the orbital period. See the next entry. User Contributions:Comment about this article, ask questions, or add new information about this topic:Top Document: [sci.astro] Solar System (Astronomy Frequently Asked Questions) (5/9) Previous Document: E.14 Earth-Moon system Next Document: E.14.2 Why does the Moon always show the same face to the Earth? Part0 - Part1 - Part2 - Part3 - Part4 - Part5 - Part6 - Part7 - Part8 - Single Page [ Usenet FAQs | Web FAQs | Documents | RFC Index ] Send corrections/additions to the FAQ Maintainer: jlazio@patriot.net
Last Update March 27 2014 @ 02:11 PM
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[sci.astro] Solar System (Astronomy Frequently Asked Questions) (5/9)
Section - E.14.1 Why doesn't the Moon rotate?
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[sci.astro] Solar System (Astronomy Frequently Asked Questions) (5/9)
Section - E.14.1 Why doesn't the Moon rotate?
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with stars, then every direction you looked would eventually end on
the surface of a star, and the whole sky would be as bright as the
surface of the Sun.
Why would anyone assume this? Certainly, we have directions where we look that are dark because something that does not emit light (is not a star) is between us and the light. A close example is in our own solar system. When we look at the Sun (a star) during a solar eclipse the Moon blocks the light. When we look at the inner planets of our solar system (Mercury and Venus) as they pass between us and the Sun, do we not get the same effect, i.e. in the direction of the planet we see no light from the Sun? Those planets simply look like dark spots on the Sun.
Olbers' paradox seems to assume that only stars exist in the universe, but what about the planets? Aren't there more planets than stars, thus more obstructions to light than sources of light?
What may be more interesting is why can we see certain stars seemingly continuously. Are there no planets or other obstructions between them and us? Or is the twinkle in stars just caused by the movement of obstructions across the path of light between the stars and us? I was always told the twinkle defines a star while the steady light reflected by our planets defines a planet. Is that because the planets of our solar system don't have the obstructions between Earth and them to cause a twinkle effect?
9-14-2024 KP