With modern astronomy one can reckon a year very precisely as being ‘365.24219879 days, or 365 days, 5 hours, 48 minutes, 45.975 seconds.’ However, in ancient times various systems were used. When one investigates the calendars of ancient India, Persia, Babylonia and Assyria, Egypt, Central and South America, and China it is interesting to notice that they uniformly had twelve thirty-day months (a few had eighteen twenty-day months) making a total of 360 days for the year and they had various methods of intercalating days so that the year would come out correctly. Although it may be strange to present-day thinking, it was common in those days to think of a 360-day year.1The more recent Jewish Calendar utilized a combination of the sun and moon:
It is called “lunar-solar” because it allowed the sun’s orbit to mark the years’ beginning but based the beginning of months on observation of the phases of the moon. The first appearance of the new moon would mark the new month. According to the Talmud, the priests would watch for this and proclaim it by sending messengers and blowing trumpets. The first problem is that the moon’s circuit is about 29 1/2 days, forcing a vacillation between a 30-day and a 29-day month; and second, that 12 of these moon/months equal 354 1/4 days, about 11 days short of the solar year. From the Babylonians the Hebrews learned to add an extra month every two or three years. In rabbinical times this “intercalary” month was inserted seven times in 19 years.2Yet we have evidence from the time of Noah that months did not alternate in length between 30 days and 29 days. The book of Genesis indicates a 5-month period as being exactly 150 days in length, or five 30-day months:
The time measurements encountered in Genesis chapters 7 and 8 are the result of a lunar calendar. Gen. 7:11 states the flood began on the seventeenth day of the second month, and it ended on the seventeenth day of the seventh month (Gen. 8:4), exactly five months. Both Gen. 7:24 and 8:3 declare the waters were upon the earth 150 days. Assuming each month is the same length, they would have 30 days apiece. Skeptics say that is a big assumption because the story does not cover an entire year, and thus doesn’t take into account any days the ancients may have added on to their year.3It appears that the earlier Jewish calendar may have been simpler than the “lunar-solar” system. “Ussher found that the ancient Jews and the Egyptians did not use a year based on the moon. Instead they had a year made up of 12 months, each 30 days long. At the end of the year they tacked on 5 days. Every 4 years they added 6 days.”4 We also have indication in Scripture that a simpler 360-day calendar is found within prophetic passages:
1 Harold Hoehner, Chronological Aspects of the Life of Christ (Grand Rapids, MI: Zondervan, 1977), 135-136.
2 Trent C. Butler, Chad Brand, Charles Draper, and Archie England, eds., Broadman and Holman Illustrated Bible Dictionary (Nashville, TN: Broadman and Holman Publishers, 2003), 252-253.
3 Charles H. Ray, “A Study of Daniel 9:24-17, Part II,” in The Conservative Theological Journal, vol. 5 no. 16 (Fort Worth, TX: Tyndale Theological Seminary, December 2001), 321.
4 James Ussher, The Annals of the World (Green Forest, AR: Master Books, 1658, c2003), 114-115.