Eight Myths About the Moon, Part II
Just because you believe a few myths about the moon doesn't mean you're a lunatic. After all, we all have our favorites. Like these four, for example.
In Part I of this article, we revealed the truth behind four myths about the moon, that calm celestial nightlight that we've all gazed upon and wondered about. In this exciting conclusion, we'll take a look at four more myths about the moon, most of which seem reasonable until examined more closely.
Myth 5: The moon doesn't rotate.
It doesn't seem to, but the moon does rotate -- very, very slowly. A lunar day is exactly as long as a lunar month. Like so many of the moons throughout the solar system, the rotation of the Earth's moon is tidally locked to its primary. Given the Earth's much larger bulk, the moon always shows the same face to us.
Therefore, this myth about the moon can't be true. Think about it. Because of the tidal lock, the moon must gradually rotate as it revolves around the Earth -- but only just enough, ironically, not to seem to move at all. (Actually the Earth and the Moon are rotating about a common center, but we won't get into that here.)
Myth 6: The phases of the moon are caused by Earth's shadow.
Actually, the only time the Earth's shadow affects the moon is during a lunar eclipse -- which, because of certain details of orbital mechanics, can only occur when the moon is perfect full. For the same reasons, you get solar eclipses only when the moon is new.
In any case, this myth about the moon is mistaken. Phases occur because of the moon's position in space. When it's between the Earth and the sun, we see only the dark hemisphere; we call this a new moon. A full moon occurs when the Earth is perfectly centered between the moon and sun.
Any other phase is a function of where the moon happens to be in its rotation around the Earth. A thin crescent means the moon isn't quite centered between the Earth and sun. One way or the other, a half-moon means its position is at right angles to the Earth-sun line-up. Simple enough, right?
Myth 7: The far side of the moon is always dark.
This myth about the moon is easy to dismiss, given a little thought. The lunar far side gets as much light as the near side -- but we never see it, due to the tidal locking. When the moon is full on the far side, it is a new moon to us. The opposite is true when our side is full moon.
Although the tide lock means we can never see all of the lunar far side without spacecraft, we can cheat a little, because the moon wobbles a bit as it moves through the sky. This idea was understood in Galileo's time, and by using it, astronomers were able to map about 60% of the moon's surface area.
Myth 8: The moon's surface is highly reflective.
Oddly enough, it isn't. The moon reflects an average of only 7% of the sunlight that falls upon it. Given that it's the brightest thing in the night sky, it's hard to believe that this myth about the moon is false, but even the brightest parts of the moon's surface are only about 30% reflective.
Hope you've enjoyed this trip to our lunar neighbor, and dispelled a few myths about the moon in the process!
