Due to Earth’s rotation around its axis, the stars and planets move across the sky from east to west. This is called diurnal motion. Over the course of twenty-four hours, a celestial object will make a complete circuit around the sky and return to about the same east-west position relative to a stargazer standing still. So every hour, an object will move about 15 degrees of arc across the sky. Remember, though, that it’s really the stargazer that’s moving, due to Earth’s rotation around its axis.