You mean the Metonic Cycle? For astronomy and calendar studies, the Metonic cycle or Enneadecaeteris (from Ancient Greek: ἐννεακαιδεκαετηρίς, "nineteen years") is a period of very close to 19 years that is remarkable for being nearly a common multiple of the solar year and the synodic (lunar) month. (from Wikipedia)The Greek astronomer Meton, in the fifth century BC, discovered that the dates of the phases of the Moon repeated exactly after a period of 19 years.
Mathematically, it uses the fact that 19 tropical years contain 6,939.60 days while 235 synodic months contain 6,939.69 days.
It can be used to predict times of eclipses. Saros Cycle is quite interesting. http://www.oarval.org/metonic.htm
Eclipses of the Sun and Moon can only occur at New or Full Moon respectively and these have to occur close to the nodes of the Moon's orbit.
The nodes are the places in the orbit where the plane of the Moon's orbit and the ecliptic cross.
The time between successive passages by the Moon through one of its nodes is called the Draconic month and equals 27.212220 days.
The time between successive New or Full Moons is called the Synodic month and equals 29.530589 days.
If we take 223 synodic months (6,585.321 days) and compare them with 242 draconic months (6,585.357 days) we can see that they are almost the same. This period is the Saros and it amounts to 18 years, 10 and a third days.
This means that eclipses can be expected in families whose members are separated by the length of the Saros. Thus knowing the date of one eclipse allows the prediction of others.
quote:
Originally posted by SnowCatcher:
I've heard about this from somewhere a few months ago, and recently the idea popped in my head on and off, but I can't seem to find anything on it. I remember reading about a long 19 year cycle - the full complete lunar cycle where the Moon returns to exact same degree & phase when you were born...I was wondering what the significance of this is, in regard to Astrology?
Quite significant. Your prenatal and postnatal eclipses are connected to historical events by the particular numbered Saros Cycle. L. Edward Johndro's "The Earth in the Heavens" is a classic on eclipses.
http://www.forex-warez.com/Free%20Download/L.Edward%20Johndro%20-%20The%20Earth%20in%20the%20Heavens/