It’s the Full Moon this weekend — on Sunday, February 5. Ever since people first looked up, they gazed at a sky dominated by two perfectly round objects — Sun and Moon. Since the Full Moon happens at midday Sunday, it will look most round just before dawn Sunday and again early that evening.
It appears round because its polar diameter is just three miles less than its equatorial width of 2,160 miles. That difference is too small to be noticeable.
Spheres are everywhere in the universe. But why don’t stars look like cigars or cubes? Answer: A sphere alone has a surface where every spot lies the same distance from the center. AND its exterior has the smallest possible area. You need more paint to cover a cube or diamond than a ball of equal weight.
So when a gas cloud or solid body contracts from its own self-gravity, it pulls itself into the smallest possible form, and that’s always a ball. Only things with low mass, like tiny moons or asteroids, lack enough gravity to do the job.
If the object spins quickly its midsection may bulge out and it’ll be thrown out of the ball club. But the Sun‘s strangely slow four-week rotation lets it keep its lovely round figure. Our lethargic Moon (which also has a four-week spin but on a much smaller body) differs from a perfect sphere by just one part in 500. To the eye, the hour of the Full Moon shows you something indistinguishable from a perfect disk, as we’ll see this weekend.
This pleased ancient cultures, who regarded the circle as the most divine shape, which we still preserve in customs like the wedding ring. Yet one rarely finds flawless natural balls here on Earth. Only in the heavens, with the Sun and Moon, did they behold such perfection. And both of those even appeared the same size, with one globe 400 times the width but also 400 times the distance of the other.
What magic is that!
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