Why do we have seasons?

Spring, summer, autumn, winter: the seasons cycle around every year, bringing warmth and cold, long days and short ones. This rhythm shapes nature, farming, and daily life all over the world. It is such a familiar pattern that we rarely ask what causes it. And when people do guess, they often get it wrong, so the seasons are a perfect example of how the real answer can be more surprising than the obvious one.

A very common guess is that seasons happen because the Earth moves closer to the Sun in summer and farther away in winter. It sounds reasonable, but it is not correct. The Earth's orbit is only very slightly oval, and that small change in distance is not what drives the seasons. In fact, the Earth is actually closest to the Sun during the Northern Hemisphere's winter. If distance were the cause, the whole planet would have summer and winter at the same time, but it does not. So the real explanation must be something else.

The true cause of the seasons is the tilt of the Earth. The Earth spins on an imaginary line through its center called its axis, and this axis is not straight up and down. It is tilted by about 23.5 degrees. Importantly, the axis keeps pointing in the same direction in space all year long. This means that as the Earth travels around the Sun, sometimes the northern half of the planet leans toward the Sun, and six months later it leans away from it.

When a hemisphere leans toward the Sun, two things happen there: the Sun's rays strike the ground more directly, delivering more energy, and the days are longer. More direct sunlight and longer days mean more warmth, and that is summer. When that same hemisphere leans away from the Sun, the rays hit at a low, slanted angle and spread their energy thinly, and the days are shorter. Less direct sunlight and shorter days mean less warmth, and that is winter. Because the two hemispheres always lean in opposite directions, they have opposite seasons at the same time.

This article was written using information from Wikipedia.