The name "sun wheel" comes from the "Solar Cross", which was a calendar used to mark the solstices and equinoxes in some pre-Christian European cultures. In addition to being represented by a wheel or cross, sometimes the sun is portrayed simply as a circle, or as a circle with a point in the centre.
As you can imagine, the sun has always been a symbol of power and magic. Because of the sun's sheer power, the Ancient Greeks made offerings of honey rather than wine, as they thought that it was important to prevent such a powerful deity from getting drunk!
The Egyptians identified several of their gods with a solar disc above the head, indicating that the deity was a god of the light.
Naturally, the sun is linked with fire and masculine energy. Call upon the sun to represent fire in ritual.