Today is the longest day of the entire year, if you live in the northern hemisphere. Because the planet Earth (the one we live on) rotates around the sun on a tilted axis, certain parts of the planet get more or less sun depending on the time of year. Basically, billions of years ago, when our solar system was being formed, tons of bits of mass collided together to form mini planets, which then collided together to form proto-planets, which eventually became most of what our planet is now. Then, another pro-planet collided with the prelude to Earth and put us on our lovely little tilt which is reasonable for the seasons. Amazing! And the seasons are a big part of why life was able to flourish on our planet. Incredible how things tend to all fall into place like that!