Blogtrek

My Third Birthday

Tonight as I was returning from an astronomy meeting I saw the full moon out. Two days from now is my birthday, and I knew that I was born just after a full moon. It was a reminder that today is my third birthday. Not of regular years, but of metonic cycles. The sun and the moon have separate motions in the sky, and we find that there is 11 days of a moon left over after 12 moons to make a full calendar year. That's too bad. Otherwise one could tell the day of the month from the lunar phase. Even after two years, the phase of the moon and the end of the year don't correspond. Not after 3, 4, or 5 years does it correspond, because the sun and moon have periods that have nothing to do with each other. They are worse than irrational, in that we can't even compute beyond about 4-6 decimal places.

But they come really close after 19 years. The link above says that 19 years is only hours removed from being 235 moons. Therefore, lunar phases will repeat approximately after 19 years. This means that since there was a new moon on 1972 July 11, for example, there will be another one on 1991 July 11, 19 years and 235 moons later.

So what is my age in metonic cycles? It is 3. It is also 57 years, or 705 moons. So since the moon was full when I was born, it is full now - it is like a birth moon for me. I wonder if my mother saw the full moon when she was pregnant, and knew she had to go to the hospital - I was coming. It is also interesting that 57 and 705 both have a 5 and a 7 in them. I was a full grown adult on my first birthday in 1965; I was working as a janitor then during the summer while earning a degree at the University of Rochester. At two cycles, I was working as an operations research analyst, constructing models of such things as maintenance and warehousing. It was the Orwellian year 1984. Now it is 2003, and a third cycle has passed. It is interesting to see how the world has changed during these periods. I have things that I could have only dreamed of having in 1984, let alone 1965 or 1946, namely cell phones, PDAs, and a computer in a small piece of luggage many times more powerful than any computer in 1984, even mainframes. The next cycle will be in 2022, when I am 76 years or 912 moons old. If I am still blogging then, I will comment on my reaching the age of 4.