The weekday, and where seven came from

An Indian almanac, the panchang, measures five things about a day. Four of them you have to look up. The fifth is the weekday, and you already know it.

The weekday is called vara. It runs from one sunrise to the next sunrise, not from midnight to midnight. So at two in the morning on a Tuesday, the almanac still says Monday. Each weekday carries the name of one of seven moving lights in the sky: the sun, the moon, and the five planets people can see without a telescope.

Why seven? Because seven is how many there are. Indian tradition also counts two more, Rahu and Ketu, but those are not objects. They are the two points where the moon's path crosses the sun's, and there is nothing there to see. They never got a day.

Now the strange part: the order. Sunday, Monday, Tuesday is not the order of anything in the sky. It is made by a rule.

Line the seven up by how long each takes to go once round the sky: Saturn, Jupiter, Mars, sun, Venus, Mercury, moon. Cut a day into 24 hours and hand them out along that list, round and round. Whoever gets the first hour owns the day.

Try it. Sunday's first hour goes to the sun. Three full rounds of seven use up 21 hours. Three hours are left: sun, Venus, Mercury. The next hour is the first hour of tomorrow, and it belongs to the moon. Monday. Keep going and the whole familiar week drops out.

This came to India from the Greek-speaking world, along with the twelve zodiac signs. It was here by the fifth century. And then it settled in completely. Tamil translated it rather than borrowing it: Sunday is just the Tamil word for the sun. In north India the spoken week mixes Sanskrit and Islamic names in one breath.