What’s an eclipse season?

View larger. | Every eclipse falls within an eclipse season. Beverley Sinclair captured this beautiful view of a total solar eclipse outside Charleston, South Carolina, on August 21, 2017, and wrote: “This photo shows the diamond ring and Baily’s beads.” Thank you, Beverley!

We’re nearly in 2022’s 1st eclipse season

We have a partial solar eclipse on April 30, 2022 and a total lunar eclipse on the night of May 15-16. We’ll call that period of time an eclipse season.

What’s an eclipse season? It’s an approximate 35-day period during which it’s inevitable for at least two (and possibly three) eclipses to take place. Typically, there are two eclipses in one eclipse season, and two eclipse seasons in one calendar year, which translates to four eclipses per year. Eclipse seasons repeat in cycles of 173.3 days (somewhat shy of six calendar months).

Why don’t you see that many eclipses then? For lunar eclipses, the moon has to be above your horizon in order for you to see a lunar eclipse. In other words, it has to be night, or close to night, and that might not always be the case during the eclipse. Solar eclipses are even harder to catch. A total solar eclipse can be seen only from a narrow track along Earth’s surface. The accompanying partial solar eclipse can be seen only in areas adjacent to that track.

2022 has 2 eclipse seasons

The April-May 2022 eclipse season will feature a partial solar eclipse on April 30 that is visible in places over the southern hemisphere. There will also be a a total lunar eclipse on May 15-16 with totality over the western hemisphere starting in CDT zones.

The October-November 2022 eclipse season will feature a partial solar eclipse on October 25 and a total lunar eclipse on November 7-8.

In 2022, the middle of the year’s first eclipse season will fall on May 15, 2022, and the middle of the second eclipse season will be November 4, 2022.

What causes an eclipse season?

There are many cycles in the heavens. An eclipse season is just one of these many celestial cycles.

Consider a scenario where the moon orbited Earth on the same plane as the Earth orbits the sun. Then we’d have a solar eclipse at every new moon, and a lunar eclipse at every full moon.

But in reality, the moon’s orbit is inclined by 5 degrees to the ecliptic (Earth’s orbital plane). Most of the time the new moon or full moon swings too far north, or south, of the ecliptic for an eclipse to take place.

For instance, in the year 2022, we will have 13 new moons and 12 full moons, but only two solar eclipses and two lunar eclipses.

In the year 2022, there are 13 new moons and 12 full moons. P = partial solar eclipse; t = total lunar eclipse. List of moon phases via AstroPixels.com.

Lunar nodes point at the sun

Twice every month, as the moon circles Earth in its orbit, the moon crosses the ecliptic (Earth’s orbital plane) at points called nodes. If the moon is going from south to north, it’s called the moon’s ascending node, and if the moon is moving from north to south, it’s called the moon’s descending node.

Read more: Node passages of the moon: 2001 to 2100

Whenever the lunar nodes point directly at the sun, that momentous event marks the middle of the eclipse season. The alignment of the moon, sun and Earth is most exact when an eclipse happens at the middle of an eclipse season, and the least so when an eclipse occurs at the start, or the end, of an eclipse season. Any lunar eclipse happening early or late in the eclipse season presents a penumbral lunar eclipse, whereas any solar eclipse happening early or late in the eclipse season features a skimpy partial eclipse of the sun.

The plane of the moon’s orbit is inclined at 5 degrees to the plane of Earth’s orbit around the sun (the ecliptic). In this diagram, however, the ecliptic is portrayed as the sun’s apparent annual path in front of the constellations of the zodiac. The moon’s orbit intersects the ecliptic at two points called nodes (labeled here as N1 and N2). It’s the middle of the eclipse season whenever this line of nodes points directly at the sun. In the above diagram, the line of nodes does not point at the sun. Image via Wikimedia Commons.

Two or 3 eclipses in one eclipse season?

An eclipse season most often presents only two eclipses. However, if the first eclipse falls early in the eclipse season, then it’s possible for a third eclipse to occur before the eclipse season ends.

The last time three eclipses happened in one eclipse season was June-July 2020:

June 5, 2020: Penumbral lunar eclipse
June 21, 2020: Annular solar eclipse
July 5, 2020: Penumbral lunar eclipse

The next time three eclipses will occur in one eclipse season will be June-July 2029:

June 12, 2029: Partial solar eclipse
June 26, 2029: Total lunar eclipse
July 11, 2029: Partial solar eclipse

Read more: How often are there 3 eclipses in a month?

Eclipse terminology

Here are some words you need to know to understand eclipse seasons: lunar nodes and ecliptic. The ecliptic is the plane of the Earth’s orbit around the sun. A lunar node is the point where, in its monthly orbit of Earth, the moon’s orbit intersects that plane. An eclipse season is when – from Earth’s perspective – the sun is close enough to a lunar node to allow an eclipse to take place. If the sun is close to a lunar node at full moon, we see a lunar eclipse. If the sun is close to a lunar node at new moon, we see a solar eclipse.

To put it another way, if the moon turns new or full in close concert with the moon’s crossing of one of its nodes, then an eclipse is not only possible – but inevitable.

Lunar nodes are where the moon’s orbit cuts through the ecliptic, or Earth-sun plane. When these nodes point directly at the sun, it marks the midpoint of an approximate 35-day eclipse season. Image via Go Science Go.

Minimum of 4 eclipses in one year

Given that the lunar month (period of time between successive new moons or successive full moons) is about 29.5 days long, a minimum of two eclipses (one solar and one lunar, in either order) happens in one eclipse season. A maximum of three eclipses is possible (either lunar/solar/lunar or solar/lunar/solar), though the first eclipse of the eclipse season has to come quite early to allow for a third eclipse near the end.

A minimum of two lunar eclipses and two solar eclipses occur in one calendar year. Yet, depending on how the eclipse seasons and lunar phases align, it’s possible to also have five, six or seven eclipses in one year.

For the maximum of seven eclipses to occur in one calendar year, the first eclipse must come in early January. That leaves enough room for the seventh eclipse in late December. In one scenario, an eclipse season sporting two eclipses comes early in the year, and late in the year. The middle eclipse season stages three eclipses.

It’s quite rare for seven eclipses to occur in one calendar year, however. Seven eclipses last happened in the year 1982, and will next occur in the year 2038.

Maximum of 7 eclipses in one year

Also, it’s remotely possible for a calendar year to sport two eclipse seasons with three eclipses each, and one eclipse from an eclipse season that straddles into the previous or following year. By way of example, we present the years 1934-35 and 1879-80.

A total solar eclipse on June 21, 2001. Image via Detroit Free Press.

Eclipses are all about alignments. In a solar eclipse, the sun, moon and Earth line up, with the moon in the middle. Image via NASA.

In a lunar eclipse, the sun, Earth and moon line up, with the Earth in the middle. Image via NASA.

Bottom line: Eclipse seasons are periods during which eclipses not only can take place, but must take place. A minimum of two eclipses (one solar and one lunar, in either order) happens in one eclipse season. A maximum of three eclipses is possible (either lunar/solar/lunar, or solar/lunar/solar). In 2022, the middle of an eclipse season falls on May 15, 2022, and then again on November 4, 2022.

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