During the active period of most showers, the radiant moves nearly one degree eastwards, parallel to the ecliptic, against the stellar background each day. This is called the radiant's diurnal drift, and is to a large degree due to the Earth's own orbital motion around the Sun, which also proceeds at nearly one degree a day. As the radiant is determined by the superposition of the motions of Earth and meteoroid, the changing orbital direction of the Earth towards the east causes the radiant to move to the east as well.