Why do we have seasons?

We have seasons because Earth tilts as it circles the Sun. As Earth travels around the Sun, its tilted axis means different parts lean toward or away from the Sun, so sunlight hits some regions more directly, others more weakly.

The Sun never turns off, and clouds blocking heat wouldn't create a whole year of repeating warm and cool periods either; both ideas miss the real, steady cause of seasons.

Because of this tilt, when one half of Earth leans toward the Sun and enjoys summer, the other half leans away and gets winter at the very same time.