Why Are the Days Longer in Summer?

WHY? is our attempt to answer all the questions every little kid asks. Do you have a question? Send it to why@mentalfloss.com.

Did you know that when it’s summer in North America it is winter in some other continents, like South America and Australia? Picture Earth as a round ball with a line drawn around the middle. That line is the equator (ee-QUAY-ter), and it divides our planet into two halves: the Northern Hemisphere (HEM-iss-feer) and the Southern Hemisphere. When it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere. In summer the days are longer, while in winter they are shorter.

On maps and globes, the Earth looks straight up and down, with the North Pole at the top and the South Pole at the bottom. Actually, though, the Earth is tilted 23.4 degrees! (A circle is 360 degrees.) This tilt is the reason that days are longer in the summer and shorter in the winter. The hemisphere that’s tilted closest to the Sun has the longest, brightest days because it gets more direct light from the Sun’s rays. One hemisphere doesn’t stay tilted closer to the Sun all year, however.

Because Earth doesn’t stay in one place! It orbits (or circles) the Sun, making an oval shape. One orbit takes one year. Because the Earth is tilted, one hemisphere will be closest to the Sun for part of the year. But as Earth continues orbiting the Sun, that tilt puts the other hemisphere closer to the Sun. In the Northern Hemisphere, the longest day of the year, called the summer solstice (SOAL-stiss), happens around June 21, because that’s when the North Pole is tilted closest to the Sun. The opposite happens around December 21: the South Pole is closest to the Sun, so the Northern Hemisphere has its shortest day of the year. Meanwhile, the Southern Hemisphere is having its own summer solstice.

Want to see it for yourself? Have an adult help you set up this fun experiment! You can also watch Bill Nye the Science Guy explain the seasons.