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LOCATION: Earth orbit
DISTANCE FROM EARTH: 225,741 to 251,967 miles (363,295 to 405,503 kilometers)
AVERAGE SURFACE TEMPERATURE: -67° F (-55° C)
LENGTH OF SPACE JOURNEY FROM EARTH TO THE MOON: 2 days
GRAVITY: If you weigh 100 pounds (45 kilograms) on Earth, you’d weigh 16.6 pounds (7.5 kilograms) here.
Roughly 140 natural satellites, called moons, orbit the various planets in our solar system, but there’s only one known simply as “the moon.” Earth’s sole satellite has loomed large in human history since ancient times. Its orbit around Earth inspired our calendar month. Its gravitational pull coaxes Earth’s oceans (and large lakes) into daily cycles of high and low tide. The moon might even affect how you toss and turn at night (one study showed that people sleep worse during a full moon). In fact, scientists suspect that our satellite’s stabilizing effect on Earth’s wobble and climates helped life evolve here. Without the moon, there might not have been moon gazers.
Our satellite is literally a chip off the old block, formed around 4.5 billion years ago when a roving body the size of Mars collided with the infant Earth and knocked a cloud of debris into orbit. That debris coalesced into the moon. But while an atmosphere protected Earth from all but the largest meteor impacts, the moon’s airless surface came under constant assault over billions of years. The powdery lunar dust is pocked by craters and dented by dark basins people once thought were seas (they’re dry, although the moon may contain ice in it deepest crevices). Our satellite is also the only heavenly body visited by human beings, whose footsteps are easy enough to follow when you touch down in your spaceship. They remain unchanged on the charcoal-gray surface.
• The moon orbits the Earth in such a way that it always shows the same side to us earthlings. We didn’t get our first glimpse of the far side—often mistakenly called the “dark side”—until a probe photographed it in 1959.
• Although various people have declared the moon as their property—and American astronauts have planted six flags on its surface—no single person or nation can claim ownership of the moon according to international law.
• The moon’s pull is slowly slowing the Earth’s rotation, but it will take millions of years for us to notice.