Earth's axis is tilted about 23.5 degrees and points the same direction all year. When your hemisphere leans toward the Sun, sunlight hits more directly and the Sun stays up longer. That is summer. Six months later the other hemisphere leans in, so the two hemispheres have opposite seasons. Distance from the Sun is not the cause: Earth is closest to the Sun in January. This week a flashlight on grid paper shows why slanted light heats less.