Many people are out late on Friday and Saturday nights for one reason or another. If you’re one of them, take a look to the east around midnight tonight, and you’ll see the last quarter moon rising with Jupiter in tow. The brilliant planet will be positioned only a few degrees below the moon in the constellation of Aries the Ram. As we move into the wee hours, the duo will rise higher and appear even more spectacular.
In binoculars, one of the moon’s most prominent “craters” is in full view tonight. Called Mare Imbrium (Sea of Showers), it’s so big, astronomers refer to it as a lunar impact basin. The mare’s dark expanse measures 712 miles across. The outermost ring is formed by the beautiful sweep of the Carpathians and Apennines to the south and southeast and the Caucasus to the east. Plato and the mountainous regions near it help define the second ring, while the smallest – only 375 miles across - is almost completely flooded over by lavas that bubbled up from the shattered crust after the impact.
Based on dating of rock samples returned from the region from the Apollo 11 and 12 missions, scientists estimate that a large asteroid struck the moon excavating the Imbrium basin 3.85 billion years ago. All three of these mountain ranges were created when heat and energy from the collision melted part of the moon’s crust and hurled billions of tons of debris across its surface.
Over the next several hundred million years, lavas rich in iron and titanium oozed from fractures in the crust and filled the basin. These cooled and crystallized like lavas on Earth into large, dark lava plains. While meteorites have continued to pepper the surface since then, most volcanic (lava) ended on the moon about 3 billion years ago.
The Sea of (monster asteroid) Showers is visible with the naked eye, too, but binoculars or a small telescope will help you see and appreciate the cool details that paint the picture of its origin.