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According to the Gregorian calendar the second month i.e. February have 28 days and in a leap year 29 days.

I am not sure what calculations(science) it takes to decide the total number of days in each month. But my questions are,

  1. Who was the first person to propose that the second month of calendar (February) will have 28 days ?
  2. Will it make any difference if we swap the total number of days of February with any other month in the calendar (say April) ?
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    $\begingroup$ If you are looking for a serious scholarly work, rather than a Russian children's book, you might want to have a look at this: onlinelibrary.wiley.com/book/10.1002/9781444396539 $\endgroup$ – fdb Dec 30 '14 at 23:05
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    $\begingroup$ In some full-fleged (no longer beta) web sites, such a questioner might be asked to show his own research, in addition to asking the question. $\endgroup$ – Gerald Edgar Dec 31 '14 at 21:16
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    $\begingroup$ To answer your second question: From the practical point of view it doesn't matter as long as the sum of the days is 365 (and you compensate that extra 6 hours per year!) , take for example the mayan calendar (I've heard mayan astronomy was more precise than its european counterpart): en.wikipedia.org/wiki/Maya_calendar#Haab.27 The origin of the length of the hours, days, weeks and months is most probably related to the religious/philosophical views of the culture in question. $\endgroup$ – hjhjhj57 Jan 3 '15 at 8:31
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The reason is simple. Baiscaly 365 (approximate number of days in a year) is not divisible on 12 (desirable number of months=the number of Zodiac signs).

Then it was proposed to have 6 months of 30 days and 6 of 31, alternating. This still was not good because 6 times 30 + 6 times 31 = 366. So one month has to be 1 day shorter. Why it was decided to make February shorter? I suppose because this was the last month of the year, which started on March 1.

This reform was made at the time of Julius Caesar (it is called Julian calendar for this reason) and naturally one month was named after him. But he was followed by an emperor whose nick name was August, who essentially established some king of monarchy, and it was decided to name a month for him as well (for everyone to know that he was not "smaller" than Julius, but perhaps even greater).

But then it did not look good that his month is shorter than July, so one day was added to August and subtracted of February. And the lengths of the remaining months were changed so they alternate. (Why exactly did they have to name after him the month which follows July, I am not sure: on my opinion, if I were charged with this, I would simply rename September or November in his honor (which are derived from Latin numerals 7 and 9; remember the first month was March!).

Please do not ask me for a reference: I read the story in my childhood, and do not remember the reference. Some Russian book for children, possibly Children's Encyclopedia.

EDIT. The above explanation is a very much simplified version of what actually happened. You can get a good impression of the complexity of the question from the Wikipedia article "Julian calendar", especially the chapters "Sacrobosco's theory on month lengths" and "Names of the months". There are also many references there.

Another interesting article is "Month" in Wikipedia, the part called "Julian and Gregorean calendars". In particular, it gives the following interesting interpretation of month lengths: they correspond to the white and black piano keys! (White correspond to 31 days and F corresponds to Jaunary:-)

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    $\begingroup$ Nice answer. But unfortunately, i can not accept it in absence of a reference. I know for person, so knowledgeable and with such a good memory, finding reference is not a big deal. :) $\endgroup$ – Amit Tyagi Dec 30 '14 at 21:13
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    $\begingroup$ @Amit Tyagi: I do not care whether you accept it or not. You asked, I answered. You can search for a reference yourself, if you do not believe me:-) $\endgroup$ – Alexandre Eremenko Dec 30 '14 at 21:20
  • $\begingroup$ I edited fdb's reference into this answer to make it complete. I can attest to this answer as well, these are just facts that we know from years of curiosity in the field. $\endgroup$ – dotancohen Dec 31 '14 at 6:17
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    $\begingroup$ I don't know why didn't I know this. Amazing! According to the Wikipedia article on Augustus, the sixth month was named after him after his death. He died on August. On the other hand, Julius Caesar was born on July and died on March. What I find a little bit strange is that the pattern is totally lost, both January and December have 31 days. $\endgroup$ – hjhjhj57 Jan 2 '15 at 9:53
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    $\begingroup$ @Javier: I agree that the real problem is "Why Jaunuary has 31 days?" $\endgroup$ – Alexandre Eremenko Jan 2 '15 at 11:04
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There is an article in Wikipedia.

The assertion that August was lengthened by (or in honor of) Augustus comes from Sacrobosco in the 13th century. (Like Alexandre, I learned this in school. But in the US.) But apparently this assertion is no longer thought to be true. For example, there is a painting of a Roman calendar from before the Julian reform showing that February already had 28 days. The Julian reform just kept that.

calendar

Answer to question:
So, according to this, the length of February was 28 days in the pre-Julian Roman calendar. Any reply attributing it to Augustus is thus wrong.

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    $\begingroup$ An interesting note in that picture. It seems 29 (as expected) is denoted XXIX; but 28 is denoted XXIIX. $\endgroup$ – Gerald Edgar Jan 3 '15 at 15:15
  • $\begingroup$ This picture depicts the 'Republican calendar' with its intercalary month en.wikipedia.org/wiki/Roman_calendar#Republican_calendar. Another surprising feature is that the first month here is January, not March. $\endgroup$ – Evargalo Oct 20 '17 at 9:21
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the 8th century BCE, they used the Calendar of Romulus, a 10-month calendar that kicked the year off in March (with the spring equinox) and ended in December. January and February didn’t even exist:

`Martius: 31 days
Aprilius: 30 days
Maius: 31 days
Junius: 30 days
Quintilis: 31 days
Sextilis: 30 days
September: 30 days
October: 31 days
November: 30 days
December: 30 days`

The Romans believed even numbers were unlucky, so Numa tried to make each month odd. But to reach the quota of 355, one month had to be even. February ended up pulling the short stick, probably because it was simply the last month on the list.

Martius: 31 days
Aprilius: 29 days
Maius: 31 days
Iunius: 29 days
Quintilis: 31 days
Sextilis: 29 days
September: 29 days
October: 31 days
November: 29 days
December: 29 days
Ianuarius: 29 days
Februarius: 28 days

Source: Mental Flows

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    $\begingroup$ The problem with your reference is that it lacks references. $\endgroup$ – hjhjhj57 Jan 6 '15 at 8:37

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