Why Is The Number Of Days In A Month Not Equal?

As a wise guy might respond, the number of days in a month is not equal because they are different!? With that bad joke aside, we can uncover the true reason why the months on our common calendar have different numbers of days. We might also want to find out why the days are distributed among the 12 months the way they are.

The days of the month were not equal even during the period of the Roman Empire. In fact, the Roman calendar changed at least once, though it was based more directly on the changes of the moon. There are 29.5 days between new moons. This is the basis for the general length of months. One of the original Roman calendars had only 10 months and the months contained either 30 or 31 days. Curiously, there were more than 60 days of winter that didn’t seem to be included in a specific month.

At one point it is reported that the Roman leaders felt even numbers were not lucky so the calendars had only 29 or 31 days. It took hundreds of years for most of the world’s population to move to the Julian calendar that had a more consistent style of marking the days. In fact, the months had alternating lengths of 30 days and 29 days. Changes to calendars were officially made by the Roman Emperor.

We currently use the Gregorian calendar, named for the man who was Pope at the time the change was made from the former calendar, the Julian. Under the Julian calendar the month’s had different numbers of days as well, though they were different from those in the Gregorian calendar. Some months of the Julian calendar already contained 31 days and remained the same. Some gained a couple of days, some gained one day to give them 30 and the original Februarius stayed the same. This month is the one that is lengthened by one day every four years.

One of the months was eliminated in the change to the Gregorian and months that had only 27 days, for example, gained an additional day or two. It’s quite interesting to note that the Julian calendar as developed under Caesar was very accurate. With months of 30 or 31 days and one month of 28 the variance over a year was only a matter of a few minutes.

But this slight discrepancy added up over the years so in 1582, under Pope Gregory, the calendar was automatically moved up 10 days and the current leap year system was established. The difference between the calendar year and the true year as determined by out sun is measured in seconds now. Not all nations adopted the Gregorian change at the time. In fact some waited until the 20th century.

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