
Our days are named for the planets and lights, from Sun-day to Saturn-day and every day in between. But their order seems strange: Sunday, Monday, Tuesday, Wednesday, Thursday, Friday and Saturday give us the heavenly bodies in this order: sun, moon, Mars, Mercury, Jupiter, Venus and Saturn.
If there seems no rhyme or reason, the answer is in this diagram. It's a code, or a way to make sense and keep track of things symbolically, just as words and numbers are. This one is very old. Dan Brown's novel has lent us the phrase Da Vinci code, and this diagram of the planets' relationships to our sense of time is a sort of Da Vinci code.
If you start at the top and follow the arrows on the star, you'll arrive at each day of the week and its planet in order, Sunday through Saturday.
On the other hand, you could trace the outer shape, starting with the moon at the bottom right. The moon, being Earth's satellite, is the closest and most rapidly moving of the heavenly bodies tracked in astrology. If you start with the moon and follow the blue line counter-clockwise, you'll read all the inner planets of the solar system in their order from the sun: Mercury, Venus, Earth, Mars, Jupiter and Saturn.
So why didn't people long ago just name the days in that order instead of creating a seven-pointed star within the heptagon to keep track of which day came next? Probably because that would have been symbolically wrong! The planetary order enshrined in the names of our days preserves the symbolic meanings of the planets as we move through the days of the week. See whether the ancient order doesn't still make a great deal of symbolic sense in modern times:
Sun is for Sunday: The week begins with the sun as the most important of the celestial bodies in the solar system. Rise and shine.
Moon is for Monday: Our Light of the Night gets second billing.
Mars is for Tuesday: The planet of initiative is next, as the week gets moving.
Mercury is for Wednesday: The link-making planet stands for our “hump-day” in the middle of the week.
Jupiter is for Thursday: The week has expanded to its fullest and reached ideal maturity.
Venus is for Friday: Everybody loves Friday. TGIF!
Saturn is for Saturday: As usual, Saturn sets the outer limit.