In the Bible, God created the Jewish calendar based on the moon. Unlike in Egypt and Babylon, where dates were calculated based on the sun, God created the Jewish calendar based on the moon. The lunar calendar has seven leap months every 19 years because the moon's rotation period is 29.5 days as seen from Earth. The Earth goes through the seasons once a year and then returns to the same place because the Earth orbits the Sun in 365 days. Therefore, if you calculate the 365 days of the Earth's rotation and the length of a year in the lunar calendar, there is a difference of 11 days, so there are seven leap months in every 19 years to make up for it.

God instituted the feasts of Sabbath, New Moon, Passover, and Sukkot based on the moon. They offered sacrifices to God every day at 9 a.m. and 3 p.m., observed the Sabbath once a week, celebrated the festival of new moons once a month, and had annual festivals such as Passover, Unleavened Bread, and Sukkot once a year.

God created the Jewish calendar at the time of the Exodus from Egypt. After being freed from Egypt 3,500 years ago, Israel wandered in the wilderness for 40 years, and the only way they were able to keep the feasts in the wilderness was by calculating the dates from the changes of the moon. The moon goes through a 29.5-day cycle of new and full moons, and when the new moon rises, it is the first day of the month, and a sacrifice called the New Moon is celebrated on this day. Thus, the moon was made to measure time, and the sun was made to mark the end of the day.

[Psalms 104:19] The moon marks off the seasons, and the sun knows when to go down.

In Israel, a day ended and a new day began at the same time in the evening when the sun set, because the sun marked the end of the day. The moon, however, was made to mark times (feasts), so that when the moon rises in the evening, the feast begins. Therefore, by making the Jewish calendar based on the moon, God signaled that the feasts begin in the evening when the moon rises. Israel's observance of Sabbaths and feasts based on evening is in accordance with the Bible and God's teachings.