Caption: A diagram illustrating nodal alginments which determine the eclipse seasons: i.e., the periods when eclipses of any kind can occur.
Features:
So eclipse seasons have a finite time length.
Whether an eclipse of any kind happens in an eclipse season depends on whether the Moon is in the right place at any time in the eclipse season.
Also, yours truly believes eclipses that happen just at the start or end of an eclipse season can NEVER be "total" eclipses But again yours truly CANNOT at this moment find a reference that says this explicitly.
In fact, most people probably consider an eclipse season a dud for lunar eclipses if there is NO total lunar eclipse. Since total lunar eclipses actually happen in only about 28.7 % of eclipse seasons (see Table: Frequency of Lunar Eclipse Types for 3000 BCE--3000 CE at Eclipse Seasons (AKA Nodal Alignments) ), most eclipse seasons are probably duds for lunar eclipses for most people.
Note also if two solar eclipses happen in an eclipse season, the lunar eclipse between them is always a total lunar eclipse (Mo-128).
See also Wikipedia: Eclipse season: Details.
sidereal year = 365.256363004 days (J2000)
For an exact gravitational two-body system of just Earth and Moon isolated in space, it would NOT rotate. But the Earth-Moon system is surrounded by other Solar System objects which exert gravitational perturbations on the Earth-Moon system.
It's enough here to say that gravitational perturbations cause the rotation of the lunar node line.
Usually there are just 2 eclipse seasons. But since 173.31 days is less than half a year (of any kind), there occasionally can be 3 eclipse seasons in a year: one near the beginning, one near the middle, and one near the end.
Credit/Permission: ©
David Jeffery,
2004 / Own work.
Image link: Itself.
Local file: local link: eclipse_season.html.
File: Eclipse file:
eclipse_season.html.