The Saros And Other Eclipse Cycles

The Saros cycle helps us understand eclipses. For an eclipse to occur, the Moon, Earth and Sun are positioned in such a way so that the Moon casts its shadow on the Sun or the Earth cast its shadow on the Moon. It helps to understand the following factors.

1.Eclipses can occur at new or full moons. The new/full moon to new/full moon cycle is measured in Synodic months.
2.Eclipses can occur when the sun “crosses” the moon’ s North or South Node.You can find a quick rundown here (The Moon has nodes instead of poles.) The sun’s movement around the moon, as it appears from Earth, is measured in Draconic months.
3.Eclipses can occur when the Moon and the Earth are closest together. That proximity is known as the perigee. The time from perigee to perigee is measured in Anomalistic months.

When the three factors – the new/full moon, sun crossing the North/South Node, and the perigee -coincide, there is an eclipse. The time from one coincidence to another is called the Saros Cycle.

There are other eclipse cycles such as the Metonic cycle which is approximately 19 years in length. The Metonic cycle is also used for computing Easter’s date.

In Mark Twain’s classic “A Connecticut Yankee in King Arthur’s Court”, the Connecticut Yankee used his ability to predict an eclipse as a sign of his wizardly powers that saved him, literally at the last minute, from being burned at the stake. The moral of the story is that you never know when eclipse cycle knowledge will come in handy.