What causes the seasons?

• A. The tilt of Earth's axis relative to its orbit around the Sun.
• B. The distance of Earth from the Sun.
• C. The speed of Earth's rotation.
• D. The size of the Sun.

Answer: (A)

Seasons are caused by the tilt of Earth's axis relative to its orbit around the Sun. Because the axis is tilted about 23.5 degrees, different hemispheres lean toward or away from the Sun as Earth travels around the Sun. When the Northern Hemisphere tilts toward the Sun, daylight lasts longer and the Sun climbs higher in the sky, so sunlight is more direct and temperatures rise (summer). Six months later, that hemisphere tilts away, days shorten, the Sun sits lower in the sky, and temperatures drop (winter). The Southern Hemisphere experiences opposite seasons at the same times. Equinoxes mark roughly equal day and night, while solstices mark the longest or shortest days. The distance from the Sun changes a little but doesn’t drive the seasons; the tilt and resulting sunlight angle and day length do. The speed of Earth’s rotation affects daily daylight, not the year-to-year seasonal pattern, and the Sun’s size isn’t changing in a way that causes seasons.