The Mountains of the Moon

When you look at the moon through binoculars or a small telescope, the first thing you notice is that the moon is divided into two distinct forms of terrain: large dark flat plains and bright mountainous highlands. Both of these are pockmarked by an enormous number of craters of all sizes.

The northern half of the moon exhibits many mountain ranges and a few isolated peaks. Credit: Starry Night software.

Early observers of the moon assumed that the large flat plains were seas, not knowing that liquid water was not available on the dry airless surface of the moon, and so named them “maria,”the Latin for “seas,”singular “mare.”“Mare”is pronounced “mah-ray,”not like a female horse. They named the lunar highlands for the mountains of Earth, not knowing that the mountains of the moon were formed by a totally different process from the mountains of Earth.

On Earth, mountains are formed by two different processes. Most mountains, and mountain ranges, are formed by tectonic action: the plates that make up the surface of the Earth bump into each other causing mountains to rise up. Other mountains on Earth are caused by volcanic action: hot magma welling up from the depths of the Earth to deposit itself on the surface as volcanoes.

The moon has neither tectonic plates nor volcanic action. Virtually all of its mountains are the result of impacts by asteroids in the distant past. Early in the moon’s history, there were many gigantic asteroids in the solar system. When these impacted the moon and planets, they formed craters far larger than the ones we see today, forming the lunar maria and leaving their rims to form lunar mountain ranges. The enormous heat generated by these impacts melted the surface material of the moon and caused it to flow, swamping some craters and mountains, which stand out now as ruins on the surface of the maria.

This chart shows some of the mountain features visible this week at the current phase of the moon, around first quarter. Several prominent craters are marked to help you get your bearings: Aristoteles, Plato, Archimedes, and Copernicus.

The mountain ranges and individual mountains are labeled with their Latin names, “montes” for mountain ranges and “mons” for individual mountains. Far over to the east are the Taurus Mountains (Montes Taurus), the landing place of the last of the manned lunar explorers, Apollo 17.

Two major mountain ranges divide the Mare Serenitatis from the Mare Imbrium: the Montes Caucasus to the north and the Montes Apenninus to the south. Where these two meet is the prominent mountain Mons Hadley, named for British optician and instrument maker John Hadley (1682–1743). This is where Apollo 15 landed in July 1971. The lunar Alps, the Montes Alpes, sweep off to the northwest, enclosing the perfect oval crater Plato.

On the barren floor of the Mare Imbrium are two of the most impressive single mountain peaks on the surface of the moon, Mons Piton and Mons Pico.

The Mons Piton has a base 16 miles (25 km.) in diameter and towers 7,380 feet (2,250 m.) over the surrounding plain. The Mons Pico is even more impressive, with a base measuring 9 x 16 miles (15 x 25 km.) and a height of 7,870 feet (2,400 m.) Both these are named after mountains on the island of Tenerife in the Canary Islands.

Although these mountains look impressive under the low light of a rising sun, they really are quite gentle when compared to the mountains of Earth. If you look again in a day or two, they will be practically invisible except for their whiter color.

Enjoy your lunar mountain climbing expedition.