I think of naming the days after planets (in more or less the same order) this system is due to a common source : Sumeria, and made popular by the Babylonians w

I think of naming the days after planets (in more or less the same order) this system is due to a common source : Sumeria, and made popular by the Babylonians who used it for their astronomy and their astrology. In fact, one could argue that in its place, naming after the days of a fortnight is more intuitive : since it coincides with the phases of the moon. Indeed, the Sanskrit way of naming days (not used popularly except in religious and astrological settings) uses a 15-day system, two in a month: The waxing phase is called the Shukla Paksha (the white part) and the waning phase is called the Krishna Paksha (the dark part): https://en.wikipedia.org/wiki/Names_of_the_days_of_the_week https://en.wikipedia.org/wiki/Names_of_the_days_of_the_week https://en.wikipedia.org/wiki/Paksha https://en.wikipedia.org/wiki/Paksha