Days of the Week

The names of the days of the week in English derive from Roman god names, similarly to the names of the planets. The gods fit for that day are naed for that day because the day has a meaning expressed by that God.
Sunday was named after the sun, because that day was dedicated to the sun and/or its worship, or worship in general. It was the 1st day o the week, and Christians continue the value of itsname by worsipping on sunday (only they do not worship a "sun god").
Monday was named for the moon an its worship, like sunday. Its name is moon-day, for it is the day dedicated to the moon like sun-day is dedicated to the sun.
Tuesday was named after Mars, the Roman god that presided over war and occaisonally law. It derives from "Tiig," "Tig," or "Tuisco," and makes tuesday a court day or a day for combating.
Wednesday's name derived from Wodin or the better known Odin, who was a god in paganism in northern Europe. The planet representing Wednesday is Mercury, who can be seen by the pagans fnorthern europe as an alias of Odin.
Thursday's name derives from the pagan god Thor, the norse god of thunder. The planet and Roman god that represents Thor is Jupiter.
Friday's name derives from being named for the Norse (pagan) goddess Frigg, who's Roman equivalent is Venus. Friday also represents the planet Venus.
Saturday is the only day that derives directly from a Roman god. The planet and the god associated with it are named saturn, which is the greek equivalent of Cronus.

The spanish calender also has similar roots, as both are named from Roman terms. The spanish monday "lunes" is deriving from "luna" meaning moon. Martes (tuesday) refers to the roman god Mars. Miercoles (wednesday) refers to the Roman god Mercury. Viernes (friday) refers to the Roman god Venus.

One can conclude from all of this stuff that basically the english and spanish calender derive from being named after Roman dieties, and the planets.