Tilt the axis with the orange knob to see what the seasons would be like on a planet with a different lean. The Sun's latitude, the tropics and the polar circles all follow the tilt. The picture is a model: sizes and distances are not to scale and the orbit is drawn as a circle. The Moon circles the Earth every 27.3 days on an orbit tilted 5.1°, drawn much closer than it really is.
Textures: Earth, Moon and Sun maps from Solar System Scope (solarsystemscope.com/textures), based on NASA imagery, licensed CC BY 4.0.
- What causes the seasons?
- The seasons are caused by the tilt of the Earth's axis, not by its distance from the Sun. The axis is tilted 23.4° and keeps pointing the same way as the Earth orbits, so for half the year the northern hemisphere leans towards the Sun (summer) and for the other half it leans away (winter). The southern hemisphere has the opposite season.
- What is the difference between a solstice and an equinox?
- At a solstice (about 21 June and 21 December) one pole leans as far as it can towards the Sun, giving the longest or shortest day. At an equinox (about 20 March and 22 September) neither pole leans towards the Sun, the Sun is overhead at the equator and day and night are about 12 hours everywhere.
- Why is it summer in Australia when it is winter in the UK?
- The tilted axis points the northern hemisphere towards the Sun while the southern hemisphere leans away, and the other way round six months later. Because the two hemispheres lean in opposite directions, their seasons are always opposite.
- What is the Midnight Sun?
- Inside the Arctic Circle (66.6° N) the tilt carries every place into permanent sunlight around the June solstice, so the Sun does not set for at least a day. Six months later the same places are in polar night and the Sun does not rise. Use the Midnight Sun and Polar night buttons to see both.
- Is the Earth closer to the Sun in summer?
- No. The Earth is closest to the Sun in early January, during northern winter, and farthest in early July. The distance changes by only about 3%, which is far too small to cause the seasons; the tilt matters much more. In this simulation the orbit is a circle.
- What would happen with no tilt?
- With no tilt the Sun would stay above the equator all year. Every place would get the same day length and Sun height every day, so there would be no seasons. Set the tilt to 0° in the simulation to see it, or push it to 45° for extreme seasons.