NASA Link - do research here
A complete explanation in pictures! - a great resource for PowerPoint presentation
While the total number of hours in the days does not change from season to
season, the number of daylight hours does.
Our planet is not oriented straight up and down with regard to its motion around the sun. It is actually tilted at an angle of 23.5 degrees off the perpendicular of its solar orbit (the same angle at which most model globes are tilted.)
As Earth travels around the sun, the axis changed the orientation of the planet with regard to the incoming solar radiation. The effect is to change the amount of light hitting the planet’s surface at any position about or below the equator.
As the seasons change from spring to autumn, the axis is oriented toward the sun. From autumn to spring, the axis is turned away from the sun. When the axis is pointed toward the sun, more light falls on that hemisphere.
During the months of April through September, there is more light on the Northern Hemisphere than on the Southern Hemisphere. The farther north one gets, the greater number of daylight hours.
Here in mid-Michigan, we are located at just under 39 degrees north latitude,
which is not quite halfway between the equator and the North Pole. This means
that during the summer we will see up to 15 ½ hours of daylight.