Are days of the week named after planets?

Some of them are.

In Old English, “Sunday” comes from Sunnandaeg, or Sun’s day, followed by “Monday” which stems from Monandaeg, or Moon’s day. The rest of the day names with which we are familiar stem from Anglo-Saxon names for gods in Teutonic mythology. Tuesday, or Tiwesdaeg, comes from Tiu, or Tiw, the Anglo-Saxon name for Tyr, the Norse God of War. Wednesday, or Wodnesdaeg, refers to Woden, or Odin, the supreme deity. Similarly, Thursday, Thursdaeg, originates from Thor, the god of thunder (corresponding to the Roman god Jupiter, or Jove). Friday, or Frigedaeg, is derived from Frigga, the wife of Woden and goddess of love and marriage. Saturday, or Saeterndaeg, refers to Saturn, the ancient Roman god of agriculture, fun, and feasting.