5 ms·

The 19-year metonic cycle (of the Jewish and Chinese calendars) has always struck me as clever but inconvenient - how do you quickly calculate if we'll have an

by h4n1 4y ago

The 19-year metonic cycle (of the Jewish and Chinese calendars) has always struck me as clever but inconvenient - how do you quickly calculate if we'll have an extra month in x years from now? The Gregorian calendar's algorithm - every 4 years, except if divisible by 100, except if also divisible by 400 - is both clever and elegant.

lupire 4y ago
All you have to do is learn astronomy. It's more civilized. Lunar calendar = more technologically advanced society.
- antognini 4y ago
  Indeed Plato considered astronomy to be the highest form of knowledge. To him it was superior to plane geometry (two-dimensional mathematics) and solid geometry (three-dimensional mathematics) since it was four-dimensional mathematics --- the study of the motion of three-dimensional objects through time.
  - dotancohen 4y ago
    I thought that the ancient Greeks considered the sky to be a 2 dimensional object: the inside of a sphere.
    - antognini 4y ago
      That conception was much older, probably in the early Archaic Age. By Plato's day it was believed that the planets were different distances from the Earth with the Moon being closest, Saturn being the farthest, and the sphere of the fixed stars being beyond that.
    - yellsatclouds 4y ago
      it sure does look like such a thing then again, everything we see is majoritarily 2 dimensional (with a whisper or soft hint of depth)
- adastra22 4y ago
  Why should our time keeping on Earth have anything to do with the moon?
  - krapp 4y ago
    Because the moon is a big bright ball in the sky which regularly moves through predictable, easily observable phases, making it an obvious basis for a system of measuring time.
    - schoen 4y ago
      The complexities, irregularities, and imprecisions of our calendars are due to things like * the Earth's rotational period ("day") * the Moon's orbital period ("month") * the Earth's orbital period ("year") not being integer multiples of each other at all! Despite that, we naturally want to keep time in terms of each of these -- as you said, they're all such extremely noticeable periodic phenomena. According to GNU units, the day is 24 hr = 86400 s (which is a historical basis for defining the second, though not the method we officially use now because we have clocks that are more consistent than the Earth's rotation), while the lunar month is 29 days + 12 hours + 44 minutes + 2.8 seconds = 2551442.8 s and the tropical year is 365.242198781 day = 31556926 s If we think of a month as a fixed whole number of days, and/or think of a year as a fixed whole number of months, and/or think of a year as fixed whole number of days, it's been known for thousands of years that we're eventually going to get in trouble astronomically and require some adjustments.
- yellsatclouds 4y ago
antognini 4y ago
It's not so hard to know if there will be an extra month using the Metonic cycle. You just add an extra month in the 3rd, 6th, 8th, 11th, 14th, 17th, and 19th years. That may sound complicated to remember, but consider how we figure out how long a month is in the Gregorian calendar. There are 30 days in the 4th, 6th, 9th, and 11th months and 28 days in the 2nd month (except for leap years). At least with the old lunisolar calendar you can figure out where you are in a month just by looking at the moon.

by h4n1 4y ago

lupire 4y ago

All you have to do is learn astronomy. It's more civilized. Lunar calendar = more technologically advanced society.

antognini 4y ago
Indeed Plato considered astronomy to be the highest form of knowledge. To him it was superior to plane geometry (two-dimensional mathematics) and solid geometry (three-dimensional mathematics) since it was four-dimensional mathematics --- the study of the motion of three-dimensional objects through time.
- dotancohen 4y ago
  I thought that the ancient Greeks considered the sky to be a 2 dimensional object: the inside of a sphere.
  - antognini 4y ago
    That conception was much older, probably in the early Archaic Age. By Plato's day it was believed that the planets were different distances from the Earth with the Moon being closest, Saturn being the farthest, and the sphere of the fixed stars being beyond that.
  - yellsatclouds 4y ago
    it sure does look like such a thing then again, everything we see is majoritarily 2 dimensional (with a whisper or soft hint of depth)
adastra22 4y ago
Why should our time keeping on Earth have anything to do with the moon?
- krapp 4y ago
  Because the moon is a big bright ball in the sky which regularly moves through predictable, easily observable phases, making it an obvious basis for a system of measuring time.
  - schoen 4y ago
    The complexities, irregularities, and imprecisions of our calendars are due to things like * the Earth's rotational period ("day") * the Moon's orbital period ("month") * the Earth's orbital period ("year") not being integer multiples of each other at all! Despite that, we naturally want to keep time in terms of each of these -- as you said, they're all such extremely noticeable periodic phenomena. According to GNU units, the day is 24 hr = 86400 s (which is a historical basis for defining the second, though not the method we officially use now because we have clocks that are more consistent than the Earth's rotation), while the lunar month is 29 days + 12 hours + 44 minutes + 2.8 seconds = 2551442.8 s and the tropical year is 365.242198781 day = 31556926 s If we think of a month as a fixed whole number of days, and/or think of a year as a fixed whole number of months, and/or think of a year as fixed whole number of days, it's been known for thousands of years that we're eventually going to get in trouble astronomically and require some adjustments.
yellsatclouds 4y ago

antognini 4y ago

It's not so hard to know if there will be an extra month using the Metonic cycle. You just add an extra month in the 3rd, 6th, 8th, 11th, 14th, 17th, and 19th years. That may sound complicated to remember, but consider how we figure out how long a month is in the Gregorian calendar. There are 30 days in the 4th, 6th, 9th, and 11th months and 28 days in the 2nd month (except for leap years). At least with the old lunisolar calendar you can figure out where you are in a month just by looking at the moon.