Also known at the Wheel of Taranis, this symbol represents the solar calendar, with points that mark the position of the sun at equinoxes and solstices.

Wikipedia extract on Taranis, the God of Thunder:

In Celtic mythology Taranis was the god of thunder worshipped in Gaul and Britain and mentioned, along with Esus and Toutatis, by the Roman poet Lucan in his epic poem Pharsalia as a Celtic deity to whom sacrificial offerings were made.[1] He was associated, as was the cyclops Brontes (‘thunder’) in Greek mythology, with the wheel and may have received human sacrifices. Many representations of a bearded god with a thunderbolt in one hand and a wheel in the other have been recovered from Gaul, where this deity apparently came to be syncretised with Jupiter.[2] He is likely connected with the Anglo-Saxon god Þunor, the Norse Thor, the Celtic Ambisagrus (likely from Proto-Celtic *Ambi-sagros = "Encircling-strength"), the Irish Tuireann and the Culdee saint Taran. The name Taranis has not yet been recovered from Gaulish inscriptions, but similar variants have, such as Taranucno-, Taranuo-, and Taraino-.