Lunar, Solar, and the Gregorian Calendars Explained

The secular calendar, beginning with January 1, that we use today was originally a religious calendar. This calendar is officially known as the Gregorian Calendar, and it was named after Pope Gregory XIII. He introduced it in 1582 to solve a religious problem.

Christianity’s calendar problem had to do with the dating of Easter. By the 16th century, scientists noted that because the average calendar year was slightly longer than the astronomical year, the holiday of Easter was forced into progressively later dates, violating the Christian-rule that Easter must fall on the Sunday after the first full moon of spring.

To fix the problem, Pope Gregory’s calendar eliminated three leap years out of every four centuries. That tiny correction stopped the slow drift of the calendar through the cycles of the sun and the seasons.

The Gregorian Calendar is a solar calendar. The earth should be (more or less) in the same location relative to the sun each year on any given date. However, not all calendars work like that.

The Islamic Calendar is a lunar calendar in which a year is made up of twelve lunar cycles with no regard for the position of the sun. As a result, Muslim holidays drift through the seasons – from spring, to winter, to fall, to summer and back again over a 33-year cycle.

The Hebrew Calendar, however, is a hybrid between solar and lunar calendars. Each month represents one lunar cycle. However, occasionally a thirteenth month must be added to the year to keep the calendar in sync with the sun and seasons.

That correction was, like the Gregorian Calendar, a response to a religious problem. According to the Torah, the holiday of Passover must fall in the season of spring (Exodus 23:15). By adding that extra month every few years, the Hebrew Calendar makes sure that Passover will not drift out of springtime, as it would in a purely lunar calendar.

Because the Hebrew Calendar also is not a purely solar calendar, dates on the Hebrew Calendar do shift back and forth each year in relationship to a solar calendar. That is why Passover can begin anywhere from late March to mid-April.

This year of 5782 is a leap year; an “extra month” is added to the calendar. In the spring of 2022 (according to the Gregorian calendar), there will be two months of Adar: Adar Aleph (the actual month of Adar) and Adar Bet (the month added during the leap year). The next leap year occur in 2024 and 2027.

Something interesting to ponder. Adar is associated with joy. So, in 2022, we have an extra month in which to be joyful. What will you do to make the most of it?