Why do the months of the year have a differing amount of days in them?

Question

I mean, there are 13 lunar months so why do we have 12 calendar months.

Answer 1

The current Gregorian calendar evolved from the Julian calendar. It is a solar (more exactly, a tropical solar) calendar, rather than a lunar calendar. Solar calendars were designed to keep the days of the year aligned with the seasons as the Earth orbits the Sun. The Julian calendar had a problem with precession because it was slightly too long. This was corrected in the Gregorian calendar, which is so named because it was decreed as the "official" calendar by Pope Gregory XIII in 1582.

There are lunar calendars currently in use, too. The Islamic calendar is a lunar calendar with 12 lunar months. It shifts by several days each year in relation to the solar calendar. There was an old English calendar that was based on 13 lunar months plus the odd day at the end of the year to realign with the solar calendar.

The Hebrew calendar is a lunisolar calendar and it's based on the lunar month with compensation to correct for drift in the solar year. It has a 19 year cycle, with an extra lunar month added 7 times during those 19 years to keep the calendar more synchronized with the solar year over the long run.

So the commonly used Gregorian calendar has evolved over many centuries from other calendars. It was the calendar decreed by the most powerful church in existence at the time, so it has become the most commonly used. The origins of a 12 month solar calendar (which was also what the Julian calendar was) may be linked to the 12 Zodiac constellations seen in the night sky.

Answer 2

No, there are only 12 1/2 lunar months in a solar year. There is no synchronizing the orbits of the moon around the Earth and the Earth around the sun. Lunar calendars correspond to lunar cycles, varying between 29 and 30 days per month. Solar calendars are subdivided into artificial months, stretched to make up for an 11 day shortage. So they are 30 and 31 days long. Yes, yes, there are anomalies, thanks to the vanities of a few Roman emperors. But fixing the calendar requires a redating effort that hasn't been undertaken since the Gregorian reform. Short of some major civil collapse, we're stuck with the calendar we have. The moon has nothing to do with it.

365 (and 1/4!) is a really odd number. You can divide 364 neatly into four 91-day quarters. Or you could divide it into 13 perfect 28-day months. But neither of these matches a lunar cycle and there is still an extra day (and 1/4!) to consider. If you tack it on as a free-for-all day, you mess with the sacred sabbath traditions. One year is exactly 52 weeks PLUS one or two days. Until we adjust the orbit of the moon (not recommended!), we'll have to live with the chaos.

Answer 3

Solar calendars have 12 months because they are designed to track the seasons, of which there are 4. 12 is divisible by 4 but 13 is not. So the average length of a month is 365.25/12 = 30.43 days. So it's necessary that they all have different lengths. Which months get 31 days and which get 30 is determined by the lengths of the seasons, which differ from each other by several days.

Answer 4

a sidereal year is about 365 days, not quite but close. if you divide by twelve you get 30 1/4 days which is awkward. divide by13 and you get 28.001 which is better but who wants 13 months so the powers that be such as Augustus Caesar and Julius Caesar and Pope Gregory 12 worked it out this way and i like it. do you

Answer 5

Just to be awkward