While we're talking about the moon

[rjpxx]

After the last two columns:

Why does the same side of the moon... (http://www.straightdope.com/classics/a2_112.html)
Why does the moon appear bigger... (http://www.straightdope.com/classics/a2_110.html)

I wondered, is it also a coincidence that the moon is just the right size and distance to block the sun during solar eclipses? It seems like it must be a very good match if we can still see the corona but not see the sun itself.

[Q.E.D.]

I wondered, is it also a coincidence that the moon is just the right size and distance to block the sun during solar eclipses?
Yes. There's no physical reason why the Moon must be the size it is. We jsut happen to be around when the right combination of the Moon's diameter and distance from us makes it appear to be roughly the same apparent diameter as the Sun. Even so, it's not always a perfect fit. Because of the shape of its orbit, sometimes the Moon is closer and sometimes it is farther away, so that some eclipses are more total than others. At some point, as the Moon recedes from us, it will never again appear large enough to completely cover the Sun anymore.

[Yllaria]

At some point, as the Moon recedes from us, it will never again appear large enough to completely cover the Sun anymore.

Awww. I'm going to MISS that.

[Q.E.D.]

Awww. I'm going to MISS that.
You'll be at least several thousand years old by then. Think your eyesight will hold out that long? ;)

[Khampelf]

You'll be at least several thousand years old by then. Think your eyesight will hold out that long? ;)


Yeah, especially if you keep looking at Solar eclispses.

[clayton_e]

Several thousand? Not to nitpick (and I'm no expert, so I may be wrong) but according to this (http://www.infidels.org/library/modern/dave_matson/young-earth/specific_arguments/moon_recede.html) site:

Let us assume, for the sake of argument, that the Moon is receding at 6 inches per year. If we go back a million years, then the Moon was 6 million inches closer to the earth. That comes to about 95 miles! Since the Moon is about 240,000 miles away, that doesn't amount to diddlysquat! Indeed, the Moon has a slightly elliptical orbit that varies more than 95 miles all by itself.

I'm no mathematician, so I won't try and figure out how many years it would take to notice any change.

[Colophon]

Of course, the moon sometimes isn't big enough to completely cover the sun, even now. If the "total" eclipse happens when the moon is too far from the Earth to completely cover the sun, you get an annular ("ring-shaped") eclipse. (Cool photo of annular eclipse (http://eclipse.span.ch/april29.htm))

There's a couple of annular eclipses next year, in South America (http://www.hermit.org/Eclipse/2005-04-08/) (actually a hybrid total/annular, but annular on land) and Spain/Africa (http://sunearth.gsfc.nasa.gov/eclipse/SEmono/ASE2005/ASE2005fig/ASE2005map1b.GIF).