Month. The calendar month is a twelfth division of the year. A solar month is the time in which the sun passes through a whole sign of the zodiac - it is 30 days, 10 hours, 29 minutes, and 5 seconds. A lunar month, or the period of one moon, is 29 days, 12 hours, 44 minutes, and 3 seconds. A civil month consists of a certain number of days, according to the laws and customs of different countries. In the year there are twelve solar months, and thirteen lunar months.