The crescent Moon and two bright pinpoints stairstep up the western sky this evening. Regulus, the star that represents the heart of the lion, is to the upper left of the Moon. And the planet Mars is about the same distance to the upper left of Regulus. The trio sets in late evening.

The largest feature on the Moon has never been seen directly by human eyes – only by robots. That’s because it’s on the Moon’s far side – the hemisphere that always faces away from us. Only a sliver of its edge can be seen from Earth. And Apollo astronauts saw only a sliver of the opposite edge.

South Pole-Aitken Basin is about 1600 miles wide – one of the largest impact features anywhere in the solar system. It probably formed when a giant asteroid slammed into the Moon soon after the Moon was born.

A Chinese lander, Chang’e 6, touched down in the basin last June. A few weeks later, it brought about four pounds of rocks and dust to Earth. Analysis of some of the samples confirmed that the basin was gouged four and a quarter billion years ago. But the dark volcanic rock that coats much of the basin formed just 2.8 billion years ago, when an ocean of magma cooled and crystallized.

Samples from the near side of the Moon indicate that it was coated with magma at the same time. So the entire lunar surface was covered by an ocean of molten rock – the side we can see, and the side we can’t.

Script by Damond Benningfield