The Eclipse Seasons

The above does not mean that there are only 70 or 80 solar eclipses spread over 13 or 14 centuries, with gaps of almost two decades between them. Eclipses are much more common than that. Dur ing an eclipse year the Sun passes through the positions of both lunar nodes, and although the Moon may not be at its node, the ecliptic limits calculated above make it possible for solar eclipses to occur during the eclipse seasons that last while the Sun is traversing those limits.

The lengths of such seasons depend upon the eclipse type in question. Consider the widest, the ecliptic limit of 18.52 degrees making partial eclipses possible. The full longitude range is a little more than 37 degrees. Because the Sun moves through slightly less than a degree of longitude per day, the eclipse seasons are over 37 days long, but they slide through our calendar year, there being two such seasons (one for the ascending and one for the descending node) in each eclipse year.

Multiple eclipses can occur within an eclipse season: because a synodic month lasts less than an eclipse season, it is feasible that there will be two solar eclipses close together. In the year 2000 there were partial eclipses on July 1 and 31; these will repeat one saros later on July 13 and August 11, 2018, and again on July 23 and August 21, 2036. Such pairings of partial eclipses are possible because of the wide ecliptic limits; the narrower limits for total eclipses are not so generous.

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