The Earth is tilted on its orbit. This causes an unequal amount of sunshine to fall in different parts of the planet during the course of a year, and this is responsible for the seasons. You can use this animation to illustrate the variations in the length of daylight, and the seasons, in the northern hemisphere.
The circles represented are:
The animation is not drawn to scale for either sizes or distances. Nor are the relative speeds of rotation and revolution accurately represented.
Click and drag the mouse to rotate.
Click on the magnifying glass to zoom in and out.