Sunday, the goddess Sol, who was the personified Sun.
Monday, after Mani, the god of the Moon.
Tuesday for Tyr, the one-armed god of war. Wednesday for Woden, better known as Odin, ruler of Asgard.
Thursday for Thor, god of lightning.
Friday after Freyja, goddess of love, sex, and violent death.
Saturday is not named after a Norse god.