An Etymological Dictionary of Astronomy and Astrophysics

A period of three → Saros cycles, that is 54 years and 34 days (19,755.96 days) that can be used to predict successive → eclipses with similar properties and location.

As the Saros cycle

is a period of about 6.585 ¹/₃ days, the ¹/₃ day means that after 223 → lunar months all eclipses are shifted by about 8 hours (or by about 120° in longitude).

Exeligmos contains a whole number of → synodic months (669), it also contains a whole number of → anomalistic months (717), and → draconistic months (726). So, after one exeligmos, the Moon will again be near the same node of its orbit. Thus we have a very good chance of finding an eclipse.

Moreover, since an exeligmos also contains a whole number of days, the eclipse will even occur at about the same time of day as before. But because the Moon moves 32° in mean longitude, over and above complete cycles, during an exeligmos, the second eclipse will occur approximately one zodiac sign farther east than did the first one (James Evans & J. Lennart Berggren, Geminos’s Introduction to the Phenomena, A Translation and Study of Hellenistic Survey of Astronomy, 2006, Princeton Univ. Press).

Etymology (EN): Exeligmos, Gk. “turn of the wheel.”

Etymology (PE): Carxgard “turn of the wheel,” from carx, → wheel, + gard “turn,” → revolve.