In the first pictures of the far side of the Moon, one feature stood out: a dark circular patch. Since those photos were snapped by a Soviet spacecraft, the feature was named the Sea of Moscow.
Most lunar “seas” are on the near side — the hemisphere that always faces Earth. In fact, seas cover about a third of the near side, but only about one percent of the far side.
The seas are plains of dark volcanic rock. They formed when asteroids punched holes in the Moon’s crust. Molten rock bubbled to the surface, filling the wide basins carved by the impacts.
The far side has about as many basins as the nearside, indicating that it got smacked just as often. But the crust is much thicker on the far side.
Current theory says the Moon probably formed when the young Earth was hit by another planet. Debris from the collision coalesced to form the Moon.
A recent idea says that Earth stayed hot for a long time after the impact. Because Earth and the Moon were much closer then, it kept the lunar near side hot as well. On the colder far side, the elements that make up the crust condensed more quickly, making the crust thicker — and hard for asteroids to punch through. But they punched through the warmer, thinner crust on the near side more often — creating the dark plains we see today.
And the Moon has a bright companion tonight. Aldebaran, the brightest star of Taurus, is to the lower left of the Moon at nightfall.
Script by Damond Benningfield