Why are the sun and moon the same size in the sky?

New Scientist ^ | 30 January 2009 | Marcus Chown

[Daffynition]

It is one of the most glorious pieces of natural theatre. Assuming you spend your life on the same part of the Earth's surface, you might witness it once - if you are particularly lucky or very long-lived, perhaps twice. But a total solar eclipse is worth the wait. At the height of totality, the fit of sun and moon is so perfect that beads of sunlight can only penetrate to us through the rugged valleys on the lunar surface, creating the stunning "diamond ring" effect.

It is all thanks to a striking coincidence. The sun is about 400 times as wide as the moon, but it is also 400 times further away. The two therefore look the same size in the sky - a unique situation among our solar system's eight planets and 166 known moons. Earth is also the only planet to harbour life. Pure coincidence?

Almost undoubtedly, say most astronomers. But perhaps it is not so much of one as the bare numbers suggest. Our moon is different. The many moons of the large outer planets - Jupiter, Saturn, Uranus and Neptune - are thought to have originated through one of two processes: from the accretion of a disc of material in the planet's gravity field, in a miniature version of the formation of the solar system's planets, or through the later gravitational capture of passing small bodies. The second possibility is also thought to account for Mars's two small satellites, Deimos and Phobos, the only other moons in the inner solar system.

But our moon is simply too big relative to Earth's own size ..........

[snip]

[mamelukesabre]

Hmmm, mine had a full sized handle, like a bicycle hand grip. Not that little guitar pick looking thing...and the balls were like billiard balls. Those look more like ping pong balls.

I remember getting it going really fast so the balls were swinging up vertical and doing what I’d guess you’d call a “double clacker clack”...then trying to get some poor kids hands or fingers smashed between the balls. IT HURT!

Oh the memories...clacker fights and smashed fingers.

I don’t know what to say about that lower contraption. It looks like the training wheel version of a REAL clacker.

[DigitalVideoDude]

Maybe you're talking about these?



And yes, I remember getting these bad boys clacking at the bottom and the top.... clack-clack-clack-clack-clack-clack. Very fast, keep your fingers out of there. (like this!)

The little cheese-ball version they sell today are simply an attempt to avoid a lawsuit.

[mamelukesabre]

THe trick(to go on the offensive) was to get the things to go side to side instead of up and down...or at least on a slant. THen chase after your opponents clacker hand before he gets yours.

OOOh! My wrist is aching just from the memory of it!