SpaceWhat causes the seasons?
The short answer, in NASA's words, is that Earth's tilted axis causes the seasons. This page explains what that means and clears up the most common wrong idea. It follows the page "What Causes the Seasons?" on NASA Space Place, read on 12 November 2026.
Not distance from the Sun
Many people believe that Earth is closer to the Sun in summer and farther in winter. It sounds sensible, and it is wrong. Earth's distance from the Sun does change a little through the year: by NASA's fact sheet it ranges from 147.1 million km to 152.1 million km. But that small change is not what makes summer and winter. If it were, the whole Earth would have summer at once. In fact the two halves of Earth have opposite seasons: when it is summer in India, it is winter in Australia.
The tilt
Earth spins on an axis, an imaginary line through the North and South Poles. That axis is not upright compared with Earth's path round the Sun. It leans over by 23.4 degrees. The lean stays pointing the same way in space all year, as Earth goes round the Sun.
So for part of the year the North Pole leans towards the Sun. Then the Sun's rays strike the northern half of Earth more directly, the days there are longer, and it is summer in the north. Half a year later Earth is on the other side of the Sun. Now the North Pole leans away, the rays strike the north at a slant, the days are shorter, and it is winter there. The southern half gets the opposite each time.
Direct rays and slanting rays
Shine a torch straight down on a table and it makes a small bright circle. Tilt the torch and the same light spreads over a larger, dimmer patch. Sunlight works the same way. Direct rays bring more heat to each patch of ground than slanting ones.
Other planets have seasons too
Any planet with a tilted axis has seasons. From NASA's fact sheet, the tilts are:
| Planet | Tilt of axis |
|---|---|
| Mercury | 0.034° |
| Venus | 177.4° |
| Earth | 23.4° |
| Mars | 25.2° |
| Jupiter | 3.1° |
| Saturn | 26.7° |
| Uranus | 97.8° |
| Neptune | 28.3° |
Figures: NASA NSSDCA Planetary Fact Sheet, last updated by NASA on 18 March 2025, read on 12 November 2026.
Mars has a tilt close to Earth's, so it has seasons much like ours, though each lasts about twice as long because its year is longer. Uranus is tipped right over on its side. Mercury and Jupiter stand almost upright and have hardly any seasons.
Try it
- Stick a pencil through an orange for an axis and tilt it. Carry it round a lamp without changing the direction of the tilt. Watch which half gets the direct light on each side of the lamp.
- Measure the length of a stick's shadow at noon once a month. The shadow is shortest in summer, when the Sun is highest.
See Earth for more of its figures, and days and years on the planets.
Source: NASA, read on 12 November 2026.