We have only 12 months in our calendar and only as many Zodiac signs as the number of months in a year. Now that we know there are 13 constellations should we not have 13 months in the calendar instead of 12 months and have 13 Zodiac Signs by adding a sign for Ophiuchus as well in the following manner?

If we have 13 months in a year, each month consisting of 28 days, we would have neat 4 weeks a month round the year which would obviously make life much easier.

But 13 months multiplied with 28 makes it only 364 days a year. So we would have to have one extra day besides 13 months each year. We may call it by any name. It could be even Xmas day or just any other day for a non-leap year. During leap years we would have to have two extra days instead of one day.

At present the period of Capricorn starts on Dec 22 and ends on Jan 19. Likewise other Zodiac periods also start from such staggered dates of various months and end on odd dates only. If we may have 13 months and may allow a year to start from Dec 22 instead of Jan 1 we would be able to resolve this anomaly also because then each Zodiac sign would begin on the 1st of each month and would end on the last day of each month only.

The way we switched over from the British system of miles, fathoms, yards,feet and inches to the metric system all over the world this reform would also obviously facilitate everybody's life enormously.

So should we not set the ball rolling to reform our calendar as conceived by me?

Deborah Houlding in her post “Understanding the Zodiac: and why there really are 12 zodiac signs” at https://www.skyscript.co.uk/zodiac.html has mentioned:

"Ophiuchus is not a new constellation, it was catalogued with many others in Ptolemy's 2nd-century treatise, Almagest, (an astronomical text of huge historical standing), where it is referred to as Septentarius, "the serpent holder". It was always realised that the ecliptic cuts through a small part of this constellation, but it is a very large constellation, the majority of which the zodiac fails to embrace, so it was not considered a "zodiac constellation"."

They knew that there were as many as 17 constellations including Ophiuchus but had deliberately chosen only twelve of them because 360 degrees could have not been equally divided into `13 sections. It indirectly implies had there been 390 degrees in a circle they would have perhaps included Ophiuchus also. Why was it necessary to divide the circle into equal widths at all? Some Zodiacs were known to cover smaller sections than the others. They could have as well accommodated even all the 17 constellations by allotting them actual widths instead of equal widths as has been done now for 13 constellations. So we may say the fact that they thought of allotting equal widths to all Zodiacs was the main culprit.

Just have a look at the current distribution, shown below.

1 ARIES = APRIL 19 – MAY 13 … 25 days 2 TAURUS = MAY 14 – JUNE 19 … 37 days 3 GEMINI = JUNE 20 – JULY 20 … 31 days 4 CANCER = JULY 21 – AUG 9 …. 21 days 5 LEO = AUGUST 10 – SEPTEMBER 15 … 37 days
6 VIRGO = SEPTEMBER 16 – OCTOBER 30 … 45 days 7 LIBRA = OCTOBER 31 – NOVEMBER 22 … 23 days 8 SCORPIO = NOVEMBER 23 – NOVEMBER 29 … 7 days 9 OPHIUCHUS = NOVEMBER 30 – DECEMBER 17 … 18 days 10 SAGITTARIUS = DECEMBER 18 – JANUARY 18 … 31 days 11 CAPRICORN = JANUARY 19 – FEBRUARY 15 … 28 days 12 AQUARIUS = FEBRUARY 16 – MARCH 11 … 24 days (in non-leap years) and 25 days (in the leap years) 13 PISCES = MARCH 12 – APRIL 18 .. 38 days

(Source: www.cool-story.com)

How nicely 365 days of the non-leap years and 366 days of the leap years have been assigned to the 13 Zodiacs?

However, as of now even if we had 13 sidereal months a year, each month of 28 days, each Zodiac would obviously not stretch over full month any way. So by having 28 days’ months and 13 months a year we would be benefited only to the extent that each month would have precisely 4 weeks while it is not so under the Gregorian calendar of 12 synodic months.

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    $\begingroup$ This is astrology not astronomy!!! $\endgroup$ – James Screech Aug 20 '16 at 7:50
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    $\begingroup$ Who cares? We divide the year into 12. It has little to do with astrology. $\endgroup$ – Rob Jeffries Aug 20 '16 at 17:51
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    $\begingroup$ I guess you could call it math if you frame it as a question of efficiency..btw, there have been numerous 13 month calendars invented throughout history $\endgroup$ – Garet Claborn Aug 21 '16 at 16:59


There is no astrophysical sense in which there are "really" 13 constellations along the ecliptic. The astronomical constellations are arbitrary regions of the sky, defined for convenience so we can refer to the locations of celestial objects (M31 in Andromeda, the nebula in Orion, and so forth). They are not designed, and are not suitable, for timekeeping.

If you look at a map of the sky, you'll see that the constellations that happen to intersect the ecliptic are not evenly spaced. If we based our calendar on them, some months would be only a few days long and others would be several weeks.

The 12 evenly spaced astrological "signs" are just as arbitrary as the astronomical constellations. Neither have any real physical basis.

If you want to argue for a 13-month year, you won't be the first to do so. -- but you can't reasonably use the constellations took support the idea.

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  • $\begingroup$ The point you're making is valid; I'd just like to point out that the regions of the sky aren't entirely pointless. Specifically some of their use in navigation comes from choosing a total set that spans the ecliptic. Just knowing the order and rough spacing is useful to track cycles and relative positioning. As you mention ofc, they're not ideal however. $\endgroup$ – Garet Claborn Aug 21 '16 at 17:21

No; generally speaking a month is based upon the natural period of the moon in orbit around the earth. The zodiac signs have nothing to do with it.


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  • $\begingroup$ We could add the month of Ophiuchus as a one day month in place of Feb 29. It'd confuse everyone, and enrage many. $\endgroup$ – Wayfaring Stranger Aug 20 '16 at 14:57

If we have 13 months a year and 13 Zodiac Signs instead of 12 months and 13 Zodiac signs instead of 12 signs as suggested by me and have "28-day months" we would be benefited yet in one more way. We shall have precisely 4 weeks per month because 7 x 4 = 28. However, it would make for only 364 days in a year. So we would have to cover this flaw by redefining the year as a period of "13 months and a leap-day" for each non-leap year and two leap-days for each leap-year.

in addition, if we may commence the 13 months-calendar from 22nd December instead of 1st January all Zodiac spells would begin on the 1st of each month and would end at the end of each month.

So my suggestion merits consideration according to me.

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – called2voyage Aug 30 '16 at 13:47

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