Although sometimes referred to as a Sun Wheel, this symbol represents the Wheel of the Year and the eight Wiccan sabbats. The term "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 center.
The sun has long been a symbol of power and magic. The Greeks honored the sun god with "prudence and piety," according to James Frazer's The Golden Bough. Because of the sun's sheer power, they made offerings of honey rather than wine -- they knew that it was important to keep a deity of such power from becoming intoxicated!
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. Invoke the sun to represent fire in ritual or for associations with the direction South. Celebrate the sun's power at Litha, the midsummer solstice, or its return at Yule.