Earth, Moon relationship means eclipses often come in pairs
Posted November 30, 2021 2:49 p.m. EST
Updated November 30, 2021 3:25 p.m. EST
There will be a total solar eclipse on Saturday. The Moon will slide in front of the Sun, casting a shadow on the Earth. Totality will be visible only from western Antarctica. People in the southernmost parts of Australia, Africa and South America may be able to see a partial eclipse.
You might recall we just saw a lunar eclipse – early the morning of Nov. 19. Is it rare for eclipses to be so closely spaced? No, this is how it always happens.
Eclipses occur in pairs (and in trios on rare occasions) because of how the Moon's orbit is tilted toward Earth's.
Eclipses fall during a pair of eclipse seasons, separated by about six months. Notice how the seasons shift earlier year by year. This is because the 354-day lunar year and 365-day calendar year do not line up very well.
Eclipses can only happen during these eclipse seasons because of a 5º tilt of the Moon's orbit toward the Earth's orbit around the Sun.
Solar eclipses occur during New Moons and lunar eclipses during Full Moons. But for much of the year, those phases come when the Moon is above or below the Earth and shadows are cast out into space.
But, twice a year, that lunar orbit wobbles around to a point where those shadows do reach the Earth (solar eclipse) and Moon (lunar eclipse).
Each eclipse season lasts 35 days on average. If a Full Moon or New Moon cross that plane early enough in an eclipse season, there is enough time to squeeze in a third eclipse when that same phase comes around 29.5 days later. This last happened in 2020 and will next happen in 2029.
Depending on where you live in the eastern United States, you have several opportunities to see an eclipse in the next two years:
- total lunar eclipse: May 15-16, 2022
the paired partial solar eclipse on April 30 will be visible from South America & Antarctica
- total lunar eclipse: Nov. 8, 2022
the paired partial solar eclipse on Oct. 25, 2022, will be visible from Europe, the Middle East and western Asia.
- partial solar eclipse: Oct. 14, 2023 and it's pair, a penumbral lunar eclipse on Oct. 28, 2023.