What causes the seasons on Earth?

SEASONS are caused by AXIAL TILT — NOT distance from the Sun. Common misconception: Earth is actually slightly CLOSER to the Sun during Northern Hemisphere winter.

Axial tilt effect: When the Northern Hemisphere tilts toward the Sun: sunlight strikes at a more direct angle (less spreading over area); days are longer; more total solar energy received = SUMMER; When tilted away: sunlight is more oblique; days are shorter; less energy received = WINTER. Southern Hemisphere has opposite seasons simultaneously. EQUINOXES (equal day/night) occur when neither hemisphere tilts toward or away — around March 20 and September 22. SOLSTICES (longest/shortest day) occur at maximum tilt — around June 21 and December 21.