In the English system, three of the 7 days of the week are obviously named after astronomical bodies - Sunday=Sun, Monday = Moon, Saturday = Saturn. The other five are named after Norse mythological beings:
Tuesday - Tiw (or Tiu), the Old English form of the sky and war god Týr.
Wednesday - Woden(or Odin), the chief deity in Norse mythology.
Thursday - named after Thor, the Norse god of thunder.
Friday - Frigg (or Frigga). Is the Norse goddess of love, marriage, and wisdom.
If you look at the French words for these days, their planetary origins are more apparent:
Tuesday is Mardi, or Mars Day.
Wednesday is Mercredi, or Mercury's day.
Thursday is Jeudi, or Jupiter's day.
Friday is Vendredi, or Venus' day.