Tilt, Rotation, and Revolution
During the March and September equinoxes, the sun strikes the Earth
with equal sunlight to the northern and southern hemispheres. During the
June and December solstices, the sun strikes the Earth with a maximum
level of sunlight on either of the hemispheres.
Depending on your location on Earth, the change in seasons can bring about changes in daylight, warmth, and other weather patterns. This change is caused by the tilt of the Earth. The constant motion around the Sun, its revolution; and the constant spinning of the Earth, its rotation; brings about days and nights and even the yearly calendar.
As you can see in the image to the right, the tilt of the Earth, in conjunction with where the planet is on its revolution, influences how the sun's rays strike the northern and southern hemispheres. This creates the change in seasons throughout the year. Along with these motions, the Earth is in a constant pull between the sun and the moon, causing a gravitational "tug-o-war" known as precession. The Northern Star, therefore, will change after every cyclic period of precession that takes around 26,000 years.