The thing I love about the Internet is the ability to answer almost any question that assumes 'ancient' knowledge. "Ancient" being anything older than a year.
I have always kind of half wondered about the name "Tuesday", in English, and how it might relate to the Spanish "Martes". I knew, of course, that Martes comes from the Latin name for Mars, the God of War. But why is the English name for the day so different when English, as a language, has borrowed so heavily from Latin and its descendant languages, like French and Spanish.
As it turns out, Tiw, or Teiwaz, was a Germanic Proto-god - and his thing was War. In an obvious adoption of the conquering Roman Theology, Mars' name, translated into the Germanic tongue, became the name of the day after Monday. Same God, different language.
How cool is that?