What is the mythology of Friday?
Our word Friday, like most of the days of the week in English,
has roots in Roman and Germanic mythology. Rome established a
system of trade all across Europe that was eventually taken over in
part by the Germanic invaders. A system of days of the week had to
be universal in order to work, so the Germans took the Roman system
and applied their own analogs.
Friday is "dies Veneris" in Latin, or Venus' Day. Venus, as you
know, is the Roman goddess of beauty. Her analog in Germanic myth
is Frigg, or Frejya. So, in German areas, Venus' Day became Frigg's
Day, or Friday.