The Face of the Moon
No doubt you’ve noticed the blazing light high in the east at sunset. The planet Jupiter rules over the rising stars of autumn and blazes until the wee hours before dawn. By 9pm it is a little to the south of the sky’s zenith; by 1am, Old Jove is high above the west horizon until finally setting in the northwest around 4am.
As if Jupiter didn’t stand out enough, it appears all the more prominent Monday and Tuesday, when it’s joined by the waxing gibbous moon. While the moon appears bigger in our skies, Jupiter is in fact more than 15,000 times larger than our moon. But because the planet is also 15,000 times farther away from us, it seems the size of a bright star.
While the moon shines bright, neither it nor the planets creates their own light. Instead, what we see is sunlight reflected from their surfaces back to us here on Earth. Looking at the moon, you’ll notice that some areas are brighter than others. Early astronomers assumed that the light areas were land and the dark areas water, hence the moon’s Sea of Serenity, the Ocean of Storms and other nautical names that endure even now when we know the moon is bereft of liquid water. Instead what we are seeing are differences in the chemical makeup of the lunar surface. Contributing the most to the moon’s distinctive face are the maria, or dark areas, vast tracts of lava left over from volcanic activity at least a billion years ago.
The lighter areas, called terrae, are ranges of mountains, dating back to the moon’s origin, that make up more than three-quarters of the lunar surface.
With no atmosphere to protect it, the moon is constantly bombarded by meteors and other space debris, which form craters, many visible from here on Earth.