If the June Moon of my imagination is now a big, juicy strawberry, then the Moon’s myriad craters are the seeds that speckle the plump fruit’s surface. There are over 800 named craters on the near side of the Moon--the hemisphere that always faces Earth. Many are observable by amateurs like you and me, through binoculars or telescopes.
The word crater is from the Latin word for cup. The Moon’s craters are bowl-like depressions caused by bombardment from rocky space debris such as asteroids and meteorites. The Earth’s atmosphere protects our planet from most hurtling hunks of debris; the friction created on entry vaporizes them. However, the Moon has no atmosphere, so it has taken quite a pummeling.
The trick to successful crater observation is to view them when they’re near the terminator. The terminator is the boundary between the illuminated and the dark portions of the Moon’s face. At the terminator, light from the Sun is striking the Moon’s surface at an angle. This fills the craters with long shadows and gives them dimension.
Break out your optical aid of choice, because we’re going crater hopping!
1) This weekend will be the best time to observe the first seven craters on my list. The final one, Grimaldi, will come into view toward the end of our observing week, Tuesday the 17th or Wednesday the 18th. They are all visible with binoculars, although good-sized binoculars like 10x50s or a modest telescope will make spotting them an easier task.
Keep in mind that the map below is a true image of the Moon. If you are using a telescope that produces a mirror-image view, remove the star diagonal in order to match the map.
2) Lunar craters bear the names of deceased scientists, scholars, artists, explorers, and astronauts who’ve made significant contributions in their fields. Some are household names, while others are a bit more obscure.
3) Find Plato. This crater is 68 miles in diameter. It is known for its dark floor, a layer of solidified lava. Plato was the ancient Greek philosopher and student of Socrates who wrote a number of enduring dialogues--conversations involving Socrates.
4) Find Copernicus. This crater is 66 miles in diameter. The feature at Copernicus’s center is uplift caused by rebound of the crater material after impact. In this case, the uplift formed three peaks rising about three-quarters of a mile above the crater floor. Nicolaus Copernicus was the Polish astronomer who first developed the scientific theory of heliocentrism, which held that the Sun was the center of the solar system and that the Earth and other planets revolved around it.
5) Find Bullialdus. This crater is 37 miles in diameter. It is circular, with a high outer rim. Ismael Bullialdus was a French astronomer who supported the works of both Galileo and Copernicus. His work on gravity laid the foundation for Isaac Newton‘s groundbreaking science.
6) Find Tycho. This distinctive, much-photographed crater is 63 miles in diameter. The eye-catching rays that fan out from Tycho like the spokes of a wheel were formed by material ejected during impact. Many astronomers believe that the presence of rays indicates a relatively young crater, by lunar standards. Ray systems around older craters may have been obliterated over time. Tycho was named for the Danish nobleman and astronomer Tycho Brahe. He is renowned for the accurate observations he made from his island observatories, as well as for the metal nose he wore to replace the piece lost in a sword duel.
7) Find Gassendi. This shallow crater is 68 miles in diameter. A much smaller crater called Gassendi A overlaps it on the northern border. Gassendi was one of the landing sites considered for Apollo 17, the final manned Moon landing. Ultimately, however, a site near Sinus Iridum (Bay of Rainbows) was selected. Pierre Gassendi was a French astronomer and priest. He was the first person to observe a planet crossing the face of the Sun (the Mercury transit of 1631), and he coined the name “Aurora Borealis” for the phenomenon of the Northern Lights.
8) Find Aristarchus. This crater is 25 miles in diameter. It is a bright crater with a prominent central peak, and it is believed to be young. Aristarchus was an ancient Greek astronomer and the first person to propose that the Sun was the center of the solar system. However, he was way ahead of his time, and his views were rejected.
9) Find Kepler. This, the smallest crater on my list, is only 19 miles in diameter. Like Tycho, it has a dramatic ray system surrounding it. It was named for Johannes Kepler, a German astronomer and imperial mathematician to Emperor Rudolph II. He is best known for his three laws of planetary motion.
10) Find Grimaldi. This, the largest crater on my list, is 107 miles in diameter. Grimaldi is a heavily eroded crater with a smooth, dark floor that makes it stand out from the surrounding, light-colored material. It sits close to the limb, the outer edge of the Moon’s disc. Francesco Grimaldi was an Italian physicist and lunar mapmaker who did early work in gravity by observing objects in free fall.
