Saros Cycle

Every 18 years and 11 days an eclipse occurs at roughly the same position in the zodiac, or to be more precise: 10 1/2 degrees further on (an eclipse occurs when either a New or Full Moon occurs close to the [[Moon's Nodes|Moon's nodal axis]]). This is a saros period. The first eclipse of a saros period is a partial eclipse that occurs as far as possible away from the Moon's nodal axis. In a partial solar or lunar eclipse the Sun (in the former case) or the Moon (in the latter) are only partially covered. With every following eclipse the amount of either the Sun or the Moon covered increases (an indication that the eclipses - whether solar or lunar - occur closer and closer to the Moon's nodal axis) until finally an eclipse occurs within the orb required for a total eclipse. After the total eclipse the process occurs in reverse with each following eclipse occurring further away from the nodal axis until the last partial eclipse of the series.

A saros cycle of solar eclipses encompasses 70 solar eclipses over a period of 1200 to 1400 years; a saros cycle of lunar eclipses encompasses around 45 lunar eclipses over a period of around 800 years.

As regards content, there are parallels between the eclipses of one saros cycle. The long periods of time involved make the saros cycle interesting for those who are involved in the astrological observation of history. It can also be of help to get a better understanding of a particular eclipse by studying other eclipses in the series, particularly the eclipse that started it.