Solving the mystery of the ancient 360-day calendar


It appears that ancient 360-day calendars may have been used globally until about the eighth century BCE., a leading internet source, has cataloged eleven different cultures that may have used them at one time. This article is an investigation into the possible source and purpose of such a calendar.

The literature indicates that 360-day calendars were used for at least two-thousand years and, in most cases, were probably an integral part of 365-day calendar systems–using intercalary periods. The question is how did all eleven of these cultures come with the same basic calendar of 360-days with twelve 30-day months which they could modify to efficiently track the seasons.

If the objective was just about tracking season, a 364-day calendar would have been much easier to live with (13-months of 28-days with each month having exactly four 7-day weeks). Add a holiday at the end of the year and you’re done. And, if your birthday, for example, was Tuesday, the 2-day of March, it would fall on Tuesday, the 2-day of March every year thereafter.

It seems unlikely that the original 360-day calendar had anything to do with tracking seasons as it would become out of sync by a full month in just 5-years and would have, almost certainly, been discarded. But, they were not discarded which would suggest that they served another purpose.

Then, there’s still the puzzling question of how the 360-day calendars were propagated. Physical barriers such as mountains, deserts and oceans that separate Mesopotamia, Mesoamerica and China would seem to preclude the merging of proprietary technologies. So, what happened?

The answer may be found in ancient Sumeria.

According to the Ancient History Encyclopedia the ancient Sumerians emerged as a culture around 5,000 BCE and lasted until about 1,750 BCE. Historically, what we call civilization, likely began in the ancient city of Eridu. As the oldest known civilization, it seemed reasonable to assume they were the first culture to embrace a 360-day calendar and so, they became the initial focus of this investigation.

The literature explained how their history and accomplishments had been lost in time–even their name. Their secrets remained buried in the deserts of Iraq until the 19th century AD, when French and British archaeologists finally stumbled upon Sumerian artifacts while hunting for evidence of the ancient Assyrians. Since then, archaeologists have recovered some 500,000 clay tablets, the majority of which are yet to be translated.


By 3,100 BC the Sumerians had already become a highly advanced and sophisticated civilization. They had a writing system (cuneiform script) and a library containing hundreds of thousands of historical documents. They also had a governmental structure and legal system and were building bridges, dams, aqueducts and irrigation systems. They are also said to have invented the wheel and plow. Mathematically, it appears that their skills were well beyond what historians had imagined. The evidence suggest that they could perform advance arithmetic calculations and may have been the initiators of the science that would later become known as astronomy. They are also said to have developed the Sexagesimal structure for measuring time–using sixty-second minutes and sixty-minute hours (like we use today) and created a measure of distance based of miles, feet and inches. It also appears that they may have mastered geometry and were able to calculate areas of rectangles, triangles and trapezoids and some believe that sophisticated geometrical calculations were being used to track the movement of planets.


Unraveling the puzzle

Over the next several years an original concept slowly began to evolve.

The Sumerians divided the 360-day year into 30 day months, the day into twelve 2-hour periods, and these periods into thirty 4-minute intervals. With 1440-minutes in a day, 4-minutes is equivalent to 1/360th of a day. That indicated that they not only divided the Earth’s orbit into intervals of 360, they also divided Earth’s rotation into intervals of 360.

Interestingly, 4-minutes X 360 = 1440-minutes (day) and 1440-minutes X 360-days = 518,400-minutes (year). When 518,400-minutes is multiplied again by 360 the result is 186,624,000 and, curiously, that number happens to be a match for a value listed in the Cannon of ancient numbers as the Earth’s orbital diameter (93,312,000-mile radius X 2). Being uneasy about the implications, I decided to let it set.

A couple of years later I was trying to make sense out of the Sexagesimal system and came up with an idea. I decided to deconstruct the 186,624,000 number that I had previously came up with by the Sexagesimal time structure of a day. First, I divided 186,624,000-miles by 360-days which resulted in 518,400-miles per-day. That figure was then divided by 24-hours which resulted in 21,600-miles per-hour. Next, 21,600-miles was divided by 60-minutes which resulted in 360-miles per-minute. Finally, the 360-miles per-minute was divided by 60-seconds which resulted in 6-miles per-second or 6-hertz (The very same as the frequency for the Earth that was insisted upon by Nicola Tesla).


To summarize what i’d learned up to that point;

  1. The cube of 360 X 4 equals 186,624,000-miles (theoretical diameter of Earth’s orbit).
  2. 186,624,000-miles is the product of a Sexagesimal year.

At this point and time, I was convinced that the Sumerians were the legitimate source of the 360-day calendar, but I was troubled by the size of discrepancy between 186,624,000-miles, the proposed diameter of Earth’s orbit, and the currently accepted value. So, once again I decided to let it set.

Several years later I came across a paper written by researcher Arnold D. Enge which got my attention. Mr. Enge had discovered that the ancient Mayan’s primary calculation for Earth’s orbit was 365.625 days rather than the 365.2422 days that is the commonly attributed. Their name for this period was “uinalhaab” or one-year. The “uinalhaab” turned out to be the missing piece of my puzzle.

It now appeared that ancient astronomers may have viewed the Earth and Moon as a system or binary pair. What follows are a couple of facts in support that supposition.

Sol-Lunar Year

A lunar-year of 354.375-days is consistent with the present-day Islamic calendar which has been in use since ancient times and the 365.625-day “uinalhaab” has now been verified by other qualified authorities. The mean of those two is precisely 360-days.


To verify the validity of the binary supposition I decided to utilize the time-distance formula that I had learned earlier (4-minutes X 360 X 360 = 518,400). But, instead of multiplying 518,400 by 360 as I had done earlier, I multiplied that figure instead by the number of days in the lunar year and the number of days in the uinalhaab.


The results as listed in the above table show that the closest approach to the Sun (semi-minor axis) is 91,854,000 miles and that the farthest approach (semi-major axis) is 94,770,000-miles. The sum of those two equal 186,624,000-miles (major axis). The preciseness of these calculations (using known values from independent sources) was enough to convince me that an Earth-Moon binary is a reasonable hypothesis.

Synodic implications

Apsidal motion of the binary pair produces twelve 30-day mini-cycles or months attributable to the Earth and thirteen 27.69230769-day mini-cycles or lunar months attributable to the Moon. The mean apsidal motion, however, is 28.8-days (see table).


The following diagram shows the outer perimeter of 365.625 days and the inner perimeter of 354.375 days with the mean solunar orbit of 360-days. The oscillating line illustrates the apsidal motion of 27.69230769 days.



How significant are these so-called mini-cycles or months? 

You be the judge.

  • 27.6923076923 X 260 = 7,200-days or 20 solunar years (Mayan Katun)
  • 30 X 360 = = 10,800-days or 30-solunar years (Saturn orbital period)

Both are significant periods and when the solunar values are converted to the 365.242 format, it’s obvious that the values reflect the Jupiter-Saturn synodic and the mean Saturn orbital period of 25.56943615 years.

Another important consideration is the synodic implication of the 354.375- and 365.625 day periods, which is 23,400-days or 65-Solunar years (below).


Why is that important?

The answer: harmonic resonance

  • Earth-Mars synodic period is 780-days X 30 = 23,400
  • Earth-Venus synodic period is 585-days X 40 = 23,400
  • Uinalhaab orbital: 365.625-days X 364 = 23,400
  • Solunar orbital: 360 X 65-days = 23,400
  • Lunar orbital: 354.5454: 66 X 360 = 23,400
  • Venus orbital: 225 X 104 = 23,400
  • Mercury orbital: 87.96992481 X 266 = 23,400

The Grand Synodic

This concludes this post.

More to follow…




Published by

The Ancient Astronomer

For the last thirteen years my full-time job has been investigating, what the scientific community refers to as, incredible coincidences. It’s kind of like putting together a really big puzzle. In the beginning the number of potential matches is bewildering. But, over the years, a few pieces of the puzzle fall into place and you begin to get a small glimpse of what the big picture may look like. Eventually, impressions are formed and at some point, those impressions need to be shared. That's what this website is all about--a platform for sharing impressions. Each post will pertain to one of the "incredible coincidences" or "unknowable".

2 thoughts on “Solving the mystery of the ancient 360-day calendar”

  1. Great article!

    2 questions though:
    1> “The ancients also had reckoned that the Earth’s circumference is 21,600 nautical miles.”. Did they?
    2> The sacred cube (4 X 360 X 360 X 360), which produces the Earth’s orbital diameter of 186,624,000 (nautical miles). You state that “the canonized book of ancient numbers” describe the same value. Which source do you mean?

    Anyways, looking forward to your next articles.

    1. Thank you very much for your comments.

      In answer to your questions;
      1. 21,600 nautical miles. Did they? – As you know, the navigational coordinates system that is used today at sea and in the air is based on the circumference of the Earth (in nautical miles) and the 360-degrees that define a circle. As one degree is 1/360 of a circle, one minute of arc is 1/21600 of a circle (or, in radians, π/10800). According to Wikipedia, these sexagesimal (base 60) units originated in Babylonian astronomy, which I believe was a technology borrowed from the Sumerians. Admittedly, this is conjecture on my part and must remain so until the vast library of undeciphered cuneiform tablets prove otherwise.

      2. Which source do you mean? – I apologize for not referencing the work of the late, great, John Michell–The Dimensions of Paradise. His book is both inspirational and challenging. Here is just a short paragraph:

      “In the operations of simple arithmetic and throughout all the numerical manifestations of nature, such as the periods and intervals of the solar system, certain “nodal” numbers occur, providing a link between processes and phenomena which otherwise appear quite unconnected with each other”

      Following are what he describes as the Canonical Dimensions for the Sun, Earth and Moon
      Diameter of sun = 864,000.00 miles
      Radius of sun = 432,000.00 miles
      Diameter of moon = 2,160.00 miles
      Radius of moon = 1,080.00 miles
      Mean diameter of earth = 7,920.00 miles
      Mean circumference of earth = 24,883.20 miles
      Mean distance from earth to moon = 237,600.00 miles
      Mean distance from earth to sun = 93,312,000.00 miles

      In Vedic Science, the distance between the Earth and Sun is the Sun’s diameter (864,000 miles) X 108 = 93,312,000 X 2 = 186,624,000-miles. One of their most brilliant researchers was the late Marion O. French (THE BHAGAVAD-GITA: ITS SCIENTIFIC ASPECT — Marion O. French).

      You may also enjoy reading my take on the ancient Mayan system. The article is now listed on


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