Many planets have moons. Earth's moon has no atmosphere to protect it, so it is covered with craters. It has daytime temperatures of 240°F (115° C) and nighttime temperatures of -260°F (-168° C). It takes 27 days to revolve around the earth and 27 days to rotate. Because of this, the same side of the moon is always facing the earth. The moon's gravity pulls on the earth as it revolves around it, causing the rise and fall of the ocean's tides. The first man walked on the moon in July 1969.