The angel of the sunlight determine how much they heat up the earth. The axel of the earth is tilted 23.5 degrees in relation ship to the sun. This is what gives us the different seasons.
When the angel is wide a specific amount of sunlight will be spread out over a big area and each part is only heated up a little. When the angel is narrow the same amount of sunlight is concentrated on a smaller area and that area is heated up much more.