Fig. 2.—Revolution of the Moon round the Earth.
9. The days of the week.
As during the moon’s circuit of the earth, the earth is also travelling on its orbit, the moon will not be between the earth and the sun again on completion of its orbit, but will have to traverse the further arc shown in the figure to come between the earth and the sun. When the moon has completed the circle of the ecliptic from the position ME, its position relative to the earth has become as NF and it has not yet come between the earth and the sun. Hence while the moon completes the circuit of the ecliptic[7] in 27 days 8 hours, the time from one new moon to another is 29 days 13 hours. Hence the nakshatras will not fall on the same days in successive lunar months, and would not be suitable as names for the days. It seems that, recognising this, the ancient astronomers had to find other names. They had the lunar fortnights of 14 or 15 days from new to full and full to new moon. Hence apparently they hit on the plan of dividing these into half and regulating the influence which the sun, moon and planets were believed to exercise over events in the world by allotting one day to each of them. They knew of five planets besides the sun and moon, and by giving a day to each of them the seven-day week was formed. The term planet signifies a wanderer, and it thus perhaps seemed suitable that they should give their names to the days which would revolve endlessly in a cycle, as they themselves did in the heavens. The names of the days are:
| Etwār or Raviwār. | Sunday. | (Ravi—the sun.) |
| Somwār. | Monday. | (Soma—the moon.) |
| Mangalwār. | Tuesday. | (Mangal or Bhauma—Mars.) |
| Budhwār. | Wednesday. | (Buddha—Mercury.) |
| Brihaspatwār or Guru. | Thursday. | (Brihaspat or Guru—Jupiter.) |
| Shukurwār. | Friday. | (Shukra—Venus.) |
| Saniwār or Sanīchara. | Saturday. | (Sani—Saturn.) |
The termination vāra means a day. The weekdays were similarly named in Rome and other countries speaking Aryan languages, and they are readily recognised in French. In English three days are named after the sun, moon and Saturn, but four, Tuesday, Wednesday, Thursday and Friday, are called after Scandinavian deities, the last three being Woden or Odin, Thor and Freya. I do not know whether these were identified with the planets. It is supposed that the Hindus obtained the seven-day week from the Greeks.[8]
10. The lunar year.
Four seven-day weeks were within a day and a fraction of the lunar month, which was the nearest that could be got. The first method of measuring the year would be by twelve lunar months, which would bring it back nearly to the same period. But as the lunar month is 29 days 13 hours, twelve months would be 354 days 12 hours, or nearly eleven days less than the tropical solar year. Hence if the lunar year was retained the months would move back round the year by about eleven days annually. This is what actually happens in the Muhammadan calendar where the twelve lunar months have been retained and the Muharram and other festivals come earlier every year by about eleven days.