Space Cycles Study Guide Rotation and revolution are the two ways in which the Earth moves. Rotation is when the earth spins on its axis. Rotation causes day and night. One rotation takes 24 hours. The Axis is the imaginary line the Earth rotates on. Earth’s axis has a tilt which causes different seasons in different parts of the world at different times. Revolution is when the Earth makes one full trip around the sun. One revolution is equal to 1 year or 365 days. Earth’s revolution causes its seasons. Orbit is the path the Earth or another object follows around the sun. Earth is one of the planets that are part of our solar system. The solar system is the sun and all the objects that orbit around it. These objects are kept in orbit by the sun’s gravity The Moon revolves around the Earth. As it revolves around the Earth, the part of the sun we can see changes. These changes are the phases of the moon. The 4 main phases are new moon, first quarter, full moon and third quarter. When the Earth casts a shadow on the moon it is called a lunar eclipse. When the Moon casts a shadow on the Earth it is called a solar eclipse. While the sun’s gravity keeps objects in orbit, the moon’s gravity causes the tides. We have 2 high tides and 2 low tides each day. Tides on opposites sides are the same.