This is a classic Druid Symbol and although it is similar to the Baptismal Cross, to call Taranis a 'cross' is a misnomer - it's a circle with spokes and represents a wheel.
And the circle of the Taranis Wheel does not represent the sun. Far from it; Taranis was the Celtic god of thunder and he used this wheel to generate lightning. As the wheel rotates on the cosmic axis, it generates sparks as it spins and we see these sparks as lightning. (Unfortunately, this implies that when no lightning occurs, the cosmos is not turning!)
The hub of the wheel represents the sun or the centre of the cosmos and there are usually more than four spokes to give the wheel strength. And let's face it; you need a pretty sturdy wheel to rotate the cosmos.
The Taranis symbol is neither a cross nor a representation of the sun, but some people refer to this as a Sun Cross.