The sun is our ultimate source of climate. Our plants and animals rely on the sun for energy and light and without it, we would perish. There is a seasonal variation in the amount of energy and light received by different parts of the earth, depending on the tilt of the earth and how far the earth has traveled around the sun. This variation influences climate everywhere in the world. But not much of the sun's radiation even reaches our atmosphere, and not all places on earth get the same amount. Relative positions of the sun and earth impact how much we get. We rely on the Greenhouse effect to capture some of the sun's energy. Read about it at the sites listed.

As the earth continues to revolve around the sun, it's also rotating around its axis like a toy top. The axis is not really anything but an invisible line passing up through the center of the earth from North Pole to South Pole.

A revolution is one complete orbit around the sun. One complete revolution is a year - 365 ¼ days. Since the earth is tilted 23 ¼ degrees on its axis, the Tropic of Cancer and the Tropic of Capricorn mark where the earth receives the most direct sunlight. Changes in season are due to this revolution, since different parts of the planet are more directly struck by sunlight at different times of the year. The four seasons are summer and winter solstices and spring and fall equinoxes. We'll learn about that next.