The Motions of the Earth and Moon

The Reason for Seasons: Earth Motions

This tilt has several ramifications.

A little more detail:

The tilt of earth's axis increases the # of summer daylight hours and decreases the # of winter daylight hours. In the image, it is summer in the northern hemisphere and the regions above the equator will remain in the sunlight for a longer time. The north pole is receiving 24 hours of daylight.
The tilt of earth's axis alters the intensity of sunlight received during different seasons - it is increased during summer and decreased during winter. This occurs because the beam of sunlight, which carries the same amount of energy, is concentrated over a smaller area in the region tilted towards the sun (where it is summer), and is spread over a larger area in the opposite hemisphere (where it is winter).

the earth's orbital motion around the sun results 
in different stars visible over the year

It's Just A Phase: Moon Motions