Heoau
02-06-2008, 12:57 AM
http://www.space.com/scienceastronomy/solarsystem/solar_eclipse_facts.html#7
What is the Saros cycle?
The Saros cycle -- hang on to your brain cells here -- exists because it takes 18 years and 10 days for the entire orbit of the Moon to precess once around in its orbit plane so that the lunar nodes make one complete revolution along the orbit. This "Nordical" period equals nearly an integer number of lunar months (223 x 29.53 days = 6,585.19 days) during each Saros cycle. Because the true length of the Saros cycle is 6,585.32 days, you have to wait three Saros cycles in order for a solar eclipse to repeat at the same spot on Earth.
Successive eclipses in the Saros cycle happen one-third of the way around the world from each other, and after three Saros cycles, the eclipse returns to nearly the same geographic location after 54 years and 33 days.
Twelve different Grand Saros eclipse series are now occurring, with the one producing the eclipses of 1937, 1955, 1973, 1991 and 2009, each having a duration near the 7.5 minute limit.
SOURCE: NASA
Example: Lunar Saros 131
http://en.wikipedia.org/wiki/Saros_cycle
As an example of a single Saros series, the accompanying table gives the dates of lunar eclipses for Saros series 131. This eclipse series began in AD 1427 with a partial eclipse at the southern edge of the Earth's shadow when the Moon was close to its descending node. Each successive Saros cycle, the Moon's orbital path is shifted northward with respect to the Earth's shadow, and the first total eclipse occurred in 1950. For the following 252 years, total eclipses occur, with the central eclipse being predicted to occur in 2078. The first partial eclipse is predicted to occur in the year 2220, and the final partial eclipse of the series will occur in 2707. The total lifetime of the lunar Saros series 131 is 1280 years.
Because of the ⅓ fraction of days in a Saros cycle, the visibility of each eclipse will differ for an observer at a given fixed locale. For the lunar Saros series 131, the first total eclipse of 1950 will not be visible to viewers in North America, as it will take place during the day, and is here labeled as down in the table. The following eclipse in the series will occur ⅓ day later, and is labeled as rising, as it will occur in the early evening. The third total eclipse occurs ⅓ day later, in the early morning, as is labeled as setting. This cycle of three (down, rising, setting) repeats from the initiation to termination of the series.
What is the Saros cycle?
The Saros cycle -- hang on to your brain cells here -- exists because it takes 18 years and 10 days for the entire orbit of the Moon to precess once around in its orbit plane so that the lunar nodes make one complete revolution along the orbit. This "Nordical" period equals nearly an integer number of lunar months (223 x 29.53 days = 6,585.19 days) during each Saros cycle. Because the true length of the Saros cycle is 6,585.32 days, you have to wait three Saros cycles in order for a solar eclipse to repeat at the same spot on Earth.
Successive eclipses in the Saros cycle happen one-third of the way around the world from each other, and after three Saros cycles, the eclipse returns to nearly the same geographic location after 54 years and 33 days.
Twelve different Grand Saros eclipse series are now occurring, with the one producing the eclipses of 1937, 1955, 1973, 1991 and 2009, each having a duration near the 7.5 minute limit.
SOURCE: NASA
Example: Lunar Saros 131
http://en.wikipedia.org/wiki/Saros_cycle
As an example of a single Saros series, the accompanying table gives the dates of lunar eclipses for Saros series 131. This eclipse series began in AD 1427 with a partial eclipse at the southern edge of the Earth's shadow when the Moon was close to its descending node. Each successive Saros cycle, the Moon's orbital path is shifted northward with respect to the Earth's shadow, and the first total eclipse occurred in 1950. For the following 252 years, total eclipses occur, with the central eclipse being predicted to occur in 2078. The first partial eclipse is predicted to occur in the year 2220, and the final partial eclipse of the series will occur in 2707. The total lifetime of the lunar Saros series 131 is 1280 years.
Because of the ⅓ fraction of days in a Saros cycle, the visibility of each eclipse will differ for an observer at a given fixed locale. For the lunar Saros series 131, the first total eclipse of 1950 will not be visible to viewers in North America, as it will take place during the day, and is here labeled as down in the table. The following eclipse in the series will occur ⅓ day later, and is labeled as rising, as it will occur in the early evening. The third total eclipse occurs ⅓ day later, in the early morning, as is labeled as setting. This cycle of three (down, rising, setting) repeats from the initiation to termination of the series.