Earth is closest to the Sun around 3 January, in the depths of northern winter, so distance cannot be what makes the seasons. The culprit is the 23.5° axial tilt, which keeps pointing the same way all the way around the orbit: whichever hemisphere leans sunward receives more direct light and longer days. The contrast sharpens with latitude until, above the polar circle at 66.5°, the Sun never sets in summer and never rises in winter, and at the pole itself six months of day run straight into six months of night.
Earth is closest to the Sun around 3 January, in the depths of northern winter, so distance cannot be what makes the seasons. The culprit is the 23.5° axial tilt, which keeps pointing the same way all the way around the orbit: whichever hemisphere leans sunward receives more direct light and longer days. The contrast sharpens with latitude until, above the polar circle at 66.5°, the Sun never sets in summer and never rises in winter, and at the pole itself six months of day run straight into six months of night.
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