The seasons change as the Earth orbits the sun. With a relatively constant axial tilt of 23.5 degrees the seasons you experience are determined entirely by the Earth’s position in orbit and which hemisphere you’re on at the time. When the N. hemisphere is tilted away from the sun, the N. hemisphere experiences Winter. When the N. hemisphere is tilted toward the sun, the N. hemisphere experiences Summer. In between these seasons we experience Spring and Fall, during the equinoxes the sun’s rays are directly over the equator.