There are a lot of interesting things about Earth’s lone natural satellite.
The nearly full Moon rises at sunset above Jiayu Pass at the west end of the Great Wall of China. The wall, now a World Heritage Site, was the largest military structure ever built. The pinkish band is the belt of Venus, and below it is Earth’s shadow.
Credit: Jeff Dai
Here’s a fun list of facts about the Moon. It’s not just for lovers, you know.
#1. The Moon is not a star or a planet, it’s a satellite. In fact, it’s Earth’s only natural satellite. (We distinguish the Moon from the vehicles we launch into space by calling them artificial satellites.) So, planets (like Earth) orbit stars (like the Sun), and satellites orbit planets. Because we know the [capital-M] Moon so well, often you’ll hear astronomers call satellites that orbit other planets “moons,” but they spell that word with a lower-case “m.”
#2. The Moon came from Earth. It didn’t form beside our planet, and Earth’s gravity didn’t capture it. The latest theory says that the Moon formed some 4½ billion years ago from debris blasted out of Earth by the impact of a body the size of Mars.
#3. The Moon and the Sun appear to be the same size. This works because the Sun’s diameter is 400 times greater than the Moon’s, but the Sun also lies 400 times as far away.
#4. Here’s a two for the price of one: The Moon takes 27.3 days to orbit Earth once, but 29.5 days to go from New Moon back to New Moon. The reason these two periods are different is because, at the same time the Moon is orbiting Earth, Earth is orbiting the Sun. So, it takes an extra 2.2 days for the three objects to once again line up at New Moon (or, really, from any phase you choose to the next time that phase appears).
#5. The Moon’s surface reflects only 12 percent of the light that falls on it. And you thought the Full Moon was bright!
#6. The Moon always keeps the same face toward Earth. Because it does, it must rotate (that is, spin) once for each orbit it makes. This may be the single biggest misconception about the Moon. Many people think that because the same face always points at us, the Moon doesn’t rotate. That’s false, and it’s easy to show how this works. Put a chair in the middle of a room. That chair will represent Earth, and you will be the Moon. Stand a few feet away from it, and face it. Also notice which wall in the room you’re facing. Next, orbit halfway around the chair, always keeping your front side toward it, and stop. A quick glance at the room will show that you’re now facing the opposite wall. Aha! For this to happen you must have rotated one-half spin. Continue around to your starting point, and you’ll see that as you orbited once, you also rotated once. Pretty cool, eh?
#7. The Moon’s average distance from Earth is 238,000 miles (383,000 kilometers). It can be as far away as 252,724 miles (406,720 kilometers) or as near as 221,439 miles (356,372 kilometers). So, the Moon can show a 14 percent change in size between the two extremes. At its average distance, and at a person’s average pace, it would take 9 years to walk to the Moon.
#8. The Moon’s diameter is 2,159 miles (3,474 kilometers). Only four satellites in our solar system are larger: Ganymede, Titan, Callisto, and Io.
#9. Here’s one related to eclipses: The Moon’s orbit tilts 5.14° to Earth’s orbit around the Sun. This is the reason we don’t have solar eclipses at every New and lunar eclipses at each Full Moon.
#10. Of the 9,113 official features on the Moon, a mere 421 are not craters. That’s only 4.6 percent.
