Why do you have seasons and why do the sunrise and sunset times change?

We have seasons because the earth is tilted. In the northern hemisphere, at the height of summer, the North Pole is tilted towards the sun. Thus the sun is high in the sky and takes longer to pass from horizon to horizon, giving us long summer days and shorter nights. The north pole has no night during the hight of summer summer, it is daytime 24 hours a day. In the mid-winter, the earth is on the other side of the sun and the north pole is therefore tilted away from the sun. Thus the sun is low in the sky and takes a shorter time to pass from horizon to horizon, giving us short winter days and longer nights. The north pole has no daylight in mid-winter and is in darkness 24 hours a day.