I wonder if the spiral on the back has anything to do with the 76 year period of Halley's comet?
I wonder if the spiral on the back has anything to do with the 76 year period of Halley's comet?
Probably not:
Callippic Cycle
From the Wikipedia article:
In astronomy and calendar studies, the Callippic cycle (or Calippic) is a particular approximate common multiple of the year (specifically the tropical year) and the synodic month, that was proposed by Callippus in 330 BC.
It is a period of 76 years, as an improvement on the 19-year Metonic cycle.
A century before Callippus, Meton invented the cycle of 19 years that counted 6,940 days, which exceeds 235 lunations by almost a third of a day, and 19 tropical years by four tenths of a day. It implicitly gave the solar year a length of 6940/19 = 365 + 1/4 + 1/76 days = 365 d 6 h 18 min 56 s. But Callippus knew that the length of the year was more closely 365 + 1/4 day (= 365d 6h 00m 00s), so he multiplied the 19-year cycle by 4 to reach an integer number of days, and then dropped 1 day from the last 19-year cycle. Thus he constructed a cycle of 76 years that contains 940 lunations and 27,759 days, and has been called the Callippic after him.