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For the last week, I have been curious about the history of the 7-day week. This led me to a curiosity around the sexagesimal (base-60) number system developed by the Sumerians over five thousand years ago. The earliest evidence of counting is the clay tokens made in standardized shapes over seven thousand years ago. These shapes included spheres, cones, cylinders and discs. They seem to have been used for numerical abstraction and record-keeping.
In a sexagesimal (base-60) number system, one counts from 1 to 59, and then 60 is represented by the same symbol as 1, now with a weight of 60. Normally, the position of the symbol is used to determine the weight. In the Sumerian system, the rightmost position represented units 1-59, the next position represented multiples of 60 (60-3540). The third position represented multiples of 3600 (3600-212400). You can see how you can represent large numbers with only a few sexagesimal symbols. Fractions were also represented in a similar way by positional symbols to the right of the main unit. There was apparently no “decimal point” and context of usage was needed to distinguish between 60, 1, and 1/60th.
In the ancient Babylonian times, it was known that lunar cycle (of 29.53 days) and the solar cycle (of 365.25 days) would synchronize every 19 years (19 * 365.25 / 29.53 = 235.007), which equals very close to 235 lunar cycles (off by 0.007 lunar month, about 2 hrs or 1/12th of a full day). This 19-year cycle would need a single day adjustment only every 12 * 19 =228 years!
WOW! I have been researching lunar and solar cycles for hours. It’s now Monday and I am still finishing this blog. I have been trying to figure out when the next alignment of the lunar and solar cycles would be. As my alignment, I have been using the winter solstice and the beginning of the lunar cycle as the Babylonians calculated it. Well, this year is the year! The winter solstice will be on December 21, 2025 (9:02am CST). And, that evening after sunset will be the first crescent moon of the new moon cycle!
surfing the universe 