Why does the moon fit almost exactly over the sun during an eclipse?

Question

The sun in size is enormous. Like placing a penny =the Earth Against a 9ft diameter disk the =Sun. yet our moon is one 6th the size of the earth. The moon fits perfectly over the suns perimiter during a solar eclipse. isnt this just amazing.?Synchronicity at its best. The moon is just in the perfect orbit for this to occur. The hand of God or just pure coincidence.

Answer 1

> The hand of God or just pure coincidence?

Well, let's see how we'd answer that question scientifically.

Step 1. First, you'd have to figure out what the chances are of this phenomenon happening "naturally". That means you'd have to analyze the known _natural_ laws for how planets are formed, how moons form, how their distances and radii are determined, how a star's radius is determined, etc. Then you could come up with some meaningful number "p" for the probability that (by natural law), the distance-to-radius ratio of a moon would be equal (plus or minus "x" percent) to the distance-to-radius ratio of the parent star.

Step 2. Having come up with a meaningful value of "p", you would then do a survey of planet-moon systems. You would have to survey significantly more than 1/p of them in order for the analysis to be meaningful. You would count the number of actual planet-moon systems (if any) that have an eclipse phenomenon similar to the earth's.

Step 3. Now that you have actual numbers, you can start to draw conclusions. Here are the cases you might find:
a) The fraction of "eclipsing" systems is approximately equal to p.
b) The fraction of eclipsing systems is significantly greater than p.
c) The fraction of eclipsing systems is significantly less than p.

In case "a", you would just conclude that nothing special is going on. If the odds are 1 in a billion, and sure enough 1 out of every billion planets is doing it, then the universe is behaving according to the laws of chance.

In cases "b" and "c", you might conclude one or the other of the following:

* "I may have made a mistake in Step 1 or Step 2. Possibly, just possibly, we don't know as much as we think we do about the natural laws of planet formation." I think most scientists have the humility to admit that, and would therefore draw this conclusion. Or:

* "This is proof of the handiwork of God." I think most scientists would consider this a very arrogant assertion to make. It would essentially be a declaration that they, the scientist, have an infallible understanding of natural law and can therefore rule out natural law as an explanation; and that they, the scientist, have a sufficient understanding of the supernatural to describe the workings of an almighty being.

But in any case, we haven't done Step 1 and Step 2 yet. Until we do, any discussion of "why" the moon fits over the sun so well, is just idle speculation and philosophy, and should not be confused with "evidence" or "science."

Answer 2

Sorry to disappoint you but it is sort of by chance, with very long odds on the probability scale (unless you believe in creationism by god, which I do not and which has even longer odds) and this is what makes it so amazing if you have ever seen one. You will never forget the experience. However the Moon does not always almost perfectly fit over the Sun. Many eclipses (not including partial ones) are in fact called "annular", where the Moon does not cover the entire discof the Sun, and the Sun shows itsef as a (very) bright circle (annulus) aroubd the Moon, weather permitting of course. Most people would not notice any significant dimming of the light unless they looked at the Sun (which is not recommended under any circumstances). This is because the Moon's orbit is not circular, it is elliptical and its' distance from Earth changes beween 356,400kn and 406,700km between its farthest point and its nearest. There is a total eclipse in parts of China next year on 1 August 2008, go see this chance occultation if you get the opportunity. As regards part 2 of your question the scientific evidence obtained from the Appollo missions mainly, and others, support the theory that the Moon was cleaved out of the Earth in a gigantic colision with a Mars sized planetisimal about 5 billion years ago during the solar systems formation. Computer simulations at astronomical research units show that this explains the size of the Moon and its distance and orbit and geological composition which all fit the facts fit very accurately. I have seen nothing to suggest anything different it is now an accepted theory explained in schools. As for its shape, all large objects such as plantets and normally stars too, naturally form into a sphere in space through their own internal gravitational attraction, unless their rotation is fast enough to ditort the shape into an oblate sphere. This is the case of the giant gas planets Jupiter and Saturn for example, or very large extreme high-rotation stars. Our own Sun is not very noticably flatter at its poles, but it is - a litlle. Some very rare ones in the galaxy do resemble cigar shapes rather than spherical so some very odd eclipses would be seen there!. Hope that answers your question.

Answer 3

The Moon usually doesn't fit perfectly over the Sun.

The Moon's orbit around the Earth is an ellipse (not a perfect circle). When a solar eclipse occurs and the Moon is at perigee, the Moon appears to be just a little bit bigger than the Sun (total eclipse). When the Moon is at apogee for a solar eclipse, the Moon appears a little bit smaller than the Sun (that's called an annular eclipse). At some point in the orbit, the Moon and Sun would appear to be exactly the same size, but that's rare.

The apparent sizes are close enough that even the total eclipses appear to have discs the same size since you can't directly compare the sizes when the Sun is behind the Moon.

Answer 4

Actually the moon is moving away from the earth at the rate of 2.8cm per year. Hence in a few million years time we will no longer be able to see total solar eclipses.

Its just pure coincidence that humans happen to be living within the time this phenomenon is occuring.

Answer 5

It's to do with the distance of the sun from the Earth, I am doing an astronomy course and have just learnt this. Because the sun is at just the right distance the moon covers it, if it were any closer it would not! If you looked at the moon and held a coin in front of it and the moved the coin closer to you and then further away, you would see that distance changes size!

Answer 6

It's an issue of distance. The moon's really close to the Earth in comparison to the sun. And no, it doesn't fit perfectly over the sun... even when they're directly aligned, the sun's light isn't blocked out and you can see it around the moon.

Answer 7

It is just something we are lucky to see right now.

The moon is slowly moving further away from the Earth, so it won't always cover the whole disc of the Sun during an eclipse.

Answer 8

The distance from the moon to earth is much smaller than that of sun to earth. The angle of vision of a very small object which is very close and that of a larger object which is very far will be the same. Hence a small object can totally mask a larger object.

Answer 9

There is no astronomical reason why the moon and the sun should fit so well. It is the sheerest of coincidences, and only the Earth among all the planets is blessed in this fashion."

Isaac Imanov.

Answer 10

coincidence... but watch who is asking the question. There is a good reason to believe that having a big moon helped evolution of life on Earth. Since we are the ones to ask the question, the randomness is a bit biased...