|Ptolemy's geocentric planetary system - Association of Gods and planets around Earth is the most probable cause of spread for the names of the seven days of the week - credit of Michael Lahanas|
Interestingly the names of the weekdays and months of the Gregorian calendar (established by Pope Gregory XIII in 1582) derive from non-Christian origins.
- Sunday: "Day of the Sun"; prayers were held to Appollo (God of the Sun in Roman mythology) to heal the sick and bring light to the world.
- Monday: "Day of the Moon", with the reference to the Moon or the Gods of Moon in ancient mythologies; succeeds Sunday since Luna - Goddess of the Moon - was sister of Appollo according to the myth (Monday is Lundi in french deriving from Luna).
- Tuesday: "Day of Tiu" or "Mars' Day" ("dies Martis" also origin of the french equivalent Mardi); Tiu or Tyr is the Norse equivalent for Mars in Roman mythology (God of war).
- Wednesday: "Woden Day" or "Mercury's day" ("dies mercuii" also origin of the french equivalent Mercredi).
- Thursday: "Thor's Day" or "Jove's day" ("dies Jovis" also origin of the french equivalent Jeudi); Thor is God of Thunder in Norse mythology with its equivalent Jove (Jupiter in Roman myth or Zeus in Greek myth), God of the Gods.
- Friday: "Day of Frigg" or "Venus' Day" ("dies Veneris" also origin of the french equivalent Vendredi); Frigg is the Goddess of marriage in Norsk myth (also wife of Thor). Venus is the Goddess of love in Roman myth (also associated with Jupiter). Thus the succession to Thursday.
- Saturday: "Day of Saturn" ("dies Saturni"); according to the myth, Saturn (God of time and agriculture) ruled before Jupiter. Public business was suspended during the mid-winter festival honoring Saturn.
- January: "Ianarius" after Janus the God of passages and new beginnings (thus the first month of the year).
- February: "Februa's month"; Februa is the Roman purification festival (which occurs around this time of the year, most probably around February 15).
- March: "Mars" after the god of war Mars, since battles were normally declared after the winter months.
- April: Most probably from "Apru" (relate to Aphrodite; which explains why it's considered by the Romans as the sacred month of Venus - the equivalent of Aphrodite).
- May: "Maia" after the Roman goddess of springtime.
- June: "Juno" after the Roman Queen of Gods, wife of Jupiter associated with marriage and birth (the summer also being symbolic for birth, explains the occurrence).
- July and August: respectively inserted in the calendar by Julius Caesar and Augustus Caesar (heir of Julius).
- September, October, November and December: from the prefixes sept- (7), oct- (8), nov- (9) and dec- (10), since they are originally the seventh to tenth months (respectively) in the Roman calendar.