Total Lunar Eclipse Had Twin in 1963

The total eclipse of the moon which took place during the night of December 29-30 was a replay of another which occurred exactly 19 years ago. The times at which the eclipses reached their maximum totality differed by only 21 minutes! In 1982, it occurred on December 30 at 1:20 A.M. Alaska Standard Time. In 1963, it was the same date at 1:10 A.M.

In fact, nearly identical eclipses occur on this date every 19 years.

This period, called the Metonic cycle, represents the time between 235 successive new moons. This does not mean that we will have to wait another 19 years for the next total eclipse of the moon--only that one will not fall on this date until then. Even so, there is still some time before another total eclipse will be visible in the western hemisphere. This will occur on April 24, 1986.

Another coincidence exists between 1982's eclipse and the one in 1963. Just nine months before each eclipse, a major volcanic eruption occurred in the tropics. In 1963 it was Mount Agung on Bali, and in 1982, El Chichon in Mexico.

The earlier eclipse has been called the "Dark Eclipse" because of the way it looked due to the quantity of volcanic dust in the atmosphere. It will be interesting to learn the results of measurements comparing the earlier event with the 1982 eclipse when El Chichon volcanic debris was still suspended in the atmosphere.