Earth is closest to the Sun in January. So why is January cold up north?
The distance changes sunlight by about 7%. Tilt changes it by far more. Guess first, then bend the orbit and the tilt until you can see which one runs the seasons.
1 · Your guess
In which month is Earth closest to the Sun?
Distances from the Wikipedia Earth infobox (secondary source, official NASA and IAU pages returned errors or were not opened). If distance drove the seasons, the whole planet would be warm in January. Instead the southern half has summer and the northern half has winter. Something else is going on.
2 · The orbit, one day at a time
3 · Sunlight over a whole year
Pick a latitude and watch the daily average sunlight at the top of the atmosphere. Dashed lines isolate each cause.
Index: 100 is the daily-mean sunlight on the equator at an equinox at mean distance. Top of atmosphere, no clouds or oceans.
4 · North against south
Same latitude, mirrored hemisphere, real Earth. The south has its summer when Earth is near perihelion, the north when it is near aphelion.
Sources and method
- Perihelion 147,098,450 km, aphelion 152,097,597 km, semi-major axis 149,598,023 km, eccentricity 0.0167086, axial tilt 23.4392811 degrees, perihelion on 3 January 2026: Wikipedia, Earth (infobox, citing VSOP87 and IERS). Secondary source, used because official sites were not opened.
- December solstice typically on 21 December, give or take a day: Wikipedia, December solstice. This page anchors the winter solstice on 21 December.
- Method: Kepler's equation for position, declination from sin(tilt) times sin(solar longitude), daily mean insolation proportional to (1/distance squared) times (h0 sin(lat) sin(decl) + cos(lat) cos(decl) sin h0). The perihelion slider shifts the orbit relative to the seasons with a simple linear rule, so values away from the real date are approximate. Dates use a 365 day year.