Why are there 28/29 days in February as opposed to 30/31 like in other months? Also who set these days?

Question

If the days are just figures to measure the year by and are abstract figures why is it that some months are shorter than others? Why couldn't we even have less months with more days or even more months with less days?

Answer 1

The term 'month' stems from the period from one full moon to the next; which is a little less than 30 days.  This is called the synodic month; because it relates to the moon's rotation in respect of the sun (the moon's rotation around the earth takes 28 days).  To ancient people, the phases of the moon were an obvious period to measure time by.  Also, there were approximately 12 such periods per year (12 X 30 = 360 days.)

Therefore, there are an extra 5 (6 in a leap year) days to be scattered among the months.  Shienara has given an excellent account of why, instead of there being 7 X 30 day months and 5 X 31 day months, there are 6 X 31 day months, 5 X 30 day months and 1 X 28 day month.

However, the phases of the moon are not exactly a 30 day cycle, so the lunar months gradually get out of step with the calendar months.  (Hence, the periods of the moon  are not regular from year to year).

In addition, during the earth's orbit about the sun, it  does not rotate exactly 365 times, but instead rotates 365+1/4 times.  Therefore, every four years, an extra day has to be added to the calendar, to bring it back into step with the Earth's orbit (or else, new year day would gradually progress through the year, a quarter of a day at a time).  Hence, for every fourth year, February has 29 days.

Why is this important? - To ensure that the calendar coincides with the seasons, which follow strictly the 365 1/4 period.  Julius Caesar declared that an extra day should be added every fourth year.  That was cqalled the 'Julian' calendar.

In fact, this is still not quite correct, and the earth actually rotates very slightly less than 365 1/4 times.  By the time of Pope Gregory, the calendar had got out of step by by 14 days, so 14 days were added to the calendar in one hit.  There were arguments, with people demanding "give us back our fourteen days!" To make up the difference in a more regular way,  three leap days are omitted every 400 years.  Hence; although 1900 was divisible by four and should have been a leap year; there was no 29 Feb in that year, because 1900 was not divisible by 400.  The year 2000, on the other hand was a leap year.  This is called the 'Gregorian' calendar; which we use ioday.

To make up for other slight variations, and for the gradual slowing down of the earth's rotation because of the gravitational drag of the sun, a 'leap second' is occasionally added.

Answer 2

The current calendar we use in the Western world traces its roots back to Roman times, but the length of the months have roots in astronomy and religon.

Answer 3

This is because Earth is at perihelion during northern hemisphere winter. When Earth is at/near perihelion it travels relatively fast--i.e. it reaches the equinox a bit earlier-- so that northern hemisphere winter is a little shorter than southern hemisphere winter. This has led to a shorter February.

Answer 4

I'm not really an expert on this but as far as I know, days and months were calculated by astrologists to coincide with the cycles of the season and the alignment of the constellations and other heavenly bodies. I remember reading about this back in high school. Supposedly there were only 30 days for the months of February, July and August. But during the days of the Roman Empire, in honor of Julius Caesar, Emperor of Rome from whose name the month of July originates, the Romans decided to add one more day to the month of July to celebrate Julius Caesar's feast day to commemorate his ascension to Godhood, consequently they did the same for August named after Julius' nephew and successor, Augustus Ceasar, thus adding an extra day for the month of July and August. Unfortunately, because the calendar has already been set, that meant the astrologists' calculations would be off by 2 extra days so they allegedly decided to just subtract the 2 days given to July and August from the month of February. As for the 28/29 days in February, I believe that's due to the calculations to compensate for the leap year. It's supposed to be a mathematical anomaly that occurs every 4 years and astrologists needed to add a day every 4 years to correct the error and to keep their computations accurate.