Eclipse season
An eclipse season is one of only two periods during each year when eclipses can occur, due to the variation in the orbital inclination of the Moon. Each season lasts about 35 days and repeats just short of six months later, thus two full eclipse seasons always occur each year. Either two or three eclipses happen each eclipse season. During the eclipse season, the inclination of the Moon's orbit is low, hence the Sun, Moon, and Earth become aligned straight enough for an eclipse to occur.
Eclipse seasons should occur 38 times within a saros period.
The type of each solar eclipse depends on the apparent sizes of the Sun and Moon, which are functions of the distances of Earth from the Sun and of the Moon from Earth, respectively, as seen from Earth's surface. These distances vary because both the Earth and the Moon have elliptic orbits.
If the Earth had a perfectly circular orbit centered around the Sun, and the Moon's orbit was also perfectly circular and centered around the Earth, and both orbits were coplanar with each other, then two eclipses would happen every lunar month. A lunar eclipse would occur at every full moon, a solar eclipse every new moon, and all solar eclipses would be the same type.
Details
An eclipse season is the only time when the Sun is close enough to one of the Moon's nodes to allow an eclipse to occur. During the season, whenever there is a full moon a lunar eclipse will occur and whenever there is a new moon a solar eclipse will occur. If the Sun is close enough to a node, then a total eclipse will occur. Each season lasts from 31 to 37 days, and seasons recur about every 6 months. At least two, and at most three eclipses, will occur during every eclipse season. This is because it is about 15 days between full moon and new moon and vice versa. If there is an eclipse at the very beginning of the season, then there is enough time for two more eclipses.In other words, because the eclipse season is longer than the synodic month, the Moon will be new or full at least two, and up to three, times during the season. Eclipse seasons occur slightly shy of six months apart, the time it takes the Sun to travel from one node to the next along the ecliptic. If the last eclipse of an eclipse season occurs at the very beginning of a calendar year, it is possible for a total of seven eclipses to occur since there is still time before the end of the calendar year for two full eclipse seasons, each having up to three eclipses.
Examples: Part 1 out of 4
Visual sequence of two particular eclipse seasons
In each sequence below, each eclipse is separated by a fortnight. The first and last eclipse in each sequence is separated by one synodic month. See also Eclipse cycles.| June 5th Descending node | June 21st Ascending node | July 5th Descending node |
| Penumbral lunar eclipse Lunar saros 111 | Annular solar eclipse Solar saros 137 | Penumbral lunar eclipse Lunar saros 149 |
| June 12th Descending node | June 26th Ascending node | July 11th Descending node |
| Partial solar eclipse Solar saros 118 | Total lunar eclipse Lunar saros 130 | Partial solar eclipse Solar saros 156 |
15-year chart of eclipses (2004–2018) demonstrating seasons
The partial lunar eclipse of August 7–8, 2017 was followed by the solar eclipse of August 21, 2017.Examples: Part 2 out of 4
Visual sequence of two particular eclipse seasons
In each sequence below, each eclipse is separated by a fortnight. The first and last eclipse in each sequence is separated by one synodic month. See also Eclipse cycles.| July 7th Ascending node | July 22nd Descending node | August 6th Ascending node |
| Penumbral lunar eclipse Lunar saros 110 | Total solar eclipse Solar saros 136 | Penumbral lunar eclipse Lunar saros 148 |
| July 13th Ascending node | July 27th Descending node | August 11th Ascending node |
| Partial solar eclipse Solar saros 117 | Total lunar eclipse Lunar saros 129 | Partial solar eclipse Solar saros 155 |
Examples: Part 3 out of 4
Visual sequence of two particular eclipse seasons
In each sequence below, each eclipse is separated by a fortnight. The first and last eclipse in each sequence is separated by one synodic month. See also Eclipse cycles.| July 6th Descending node | July 20th Ascending node | August 4th Descending node |
| Penumbral lunar eclipse Lunar saros 109 | Annular solar eclipse Solar saros 135 | Penumbral lunar eclipse Lunar saros 147 |
| July 11th Descending node | July 26th Ascending node | August 9th Descending node |
| Partial solar eclipse Solar saros 116 | Total lunar eclipse Lunar saros 128 | Partial solar eclipse Solar saros 154 |
Examples: Part 4 out of 4
Visual sequence of two particular eclipse seasons
In each sequence below, each eclipse is separated by a fortnight. The first and last eclipse in each sequence is separated by one synodic month. See also Eclipse cycles.| July 21st Ascending node | August 4th Descending node | August 20th Ascending node |
| Partial solar eclipse Solar saros 115 | Total lunar eclipse Lunar saros 127 | Partial solar eclipse Solar saros 153 |
| July 26th Ascending node | August 10th Descending node | August 24th Ascending node |
| Penumbral lunar eclipse Lunar saros 108 | Annular solar eclipse Solar saros 134 | Penumbral lunar eclipse Lunar saros 146 |