Doorstep Astronomy: The 9-Day-Old Moon
The 9-day-old gibbous moon.
Credit: Starry Night Software

If you look at the moon in the next night or two with binoculars or a small telescope, you will be able to see a number of interesting features.

At the current phase of the moon, the northern half is mainly a large plain of lava known as the Mare Imbrium, Latin for Sea of Rains. This rather fanciful name was given to the area by Riccioli in 1651, before we knew that the moon had no seas and no atmosphere, hence no weather. This plain is 720 miles in diameter (1160 km.)

The Mare Imbrium is bordered by the Lunar Alps on the north. Nestled in the alps is the beautiful crater Plato, 63 miles in diameter (101 km.), with a smooth flat floor resulting from a lava flow. There are a number of tiny craterlets on the floor of Plato which are often used as test targets for large telescopes. Although Plato appears oval from Earth, this is an effect of perspective and the crater is, in fact, round.

On the southern rim of the Mare Imbrium is lunar Apennine mountain chain, with the complex crater Eratosthenes on the terminator, the boundary between light and shadow. Eratosthenes is a terraced crater 36 miles in diameter (58 km.) with a large central peak. It is a miniature version of the mighty crater Copernicus, still in shadow to the west.

Sweeping further south along the terminator you will soon see one of the most spectacular features on the lunar surface: the Rupes Recta, known in English as the Straight Wall. This is a fault line 68 miles long (110 km.) When lit by the rising sun, it looks like a high steep cliff, but in fact its slope is quite gentle and its height less than 985 feet (300 meters).

Between the Straight Wall and the moon?s south pole you will find one of the largest craters on the moon, Clavius, 140 miles in diameter (225 km.) This huge mountainous ring contains a series of ever smaller many can you count?

These are just the highlights of one of the richest areas on the moon. A good map like the one by Antonin Rukl available from Sky Publishing will guide you to hundreds more objects.

This article was provided to by Starry Night Education, the leader in space science curriculum solutions.