No, It’s Not An ‘Annual’ Solar Eclipse. Discover The Celestial Cycle Behind This Week’s ‘Ring Of Light’ Solar Eclipse
Go type “annular” into your word processing software. It got changed to “annual,” right?
The rare solar eclipse coming to North America on June 10, 2021 is one that commonly gets mis-named and, therefore, completely misunderstood.
So let’s clear this up: there is no such thing as an “annual solar eclipse.”
What happens on June 10, 2021 will be an annular solar eclipse. Here’s everything you need to know about the science that makes it happen:
Annular means ring-shaped—hence the colloquial term “ring of fire” (though “ring of light” is more accurate). During this event 89% of the Sun will be blocked by the Moon—as seen from a path through Canada, Greenland and Russia—to create a bright ring around the Sun. Much of northeast U.S. will see a big partial eclipse of the Sun around sunrise. Everyone will have to wear solar eclipses glasses and use solar filters on their cameras and telescopes.
So the “annual” thing is a complete mis-type or auto-correct? Don’t solar eclipses happen every year? Well, actually, yes they do—usually—but there is no annual pattern whatsoever. It’s way more intricate and incredible than that.
MORE FOR YOU
“About every 18 months” is usually what’s quoted for the recurrence of a particular kind of solar eclipse, but that’s not actually correct. Here are the annular solar eclipses coming up in the next decade:
June 10, 2021
October 14, 2023
October 2, 2024
February 17, 2026
February 6, 2027
January 26, 2028
June 1, 2030
May 21, 2031
You can see no pattern at all, right? And yet there is usually an annular solar eclipse every year or two. So what’s going on?
Rather, eclipses of the Sun and Moon occur every Saros—Greek for cycle. A Saros lasts for 6,585 days—18 years, 11 days and eight hours. Every Saros the Sun, Moon and Earth come full circle and for a few brief minutes they line-up to cause a spectacular totality (or annularity, which depends on the distance of the Moon from Earth).
The eclipses in the same Saros throw a shadow onto the Earth that’s incredibly similar in geometry. The 18 years, 11 days difference means their date drifts 11 days forward for each subsequent eclipse, and the eight hours means that the Earth rotates a third, so the path shifts roughly 120º west.
This pattern repeats, though each Saros begins as a set of repeating partial solar solar eclipses, then becomes annular, then total, then annular, then partial again before fizzling out. This process takes centuries.
Let’s take this week’s solar eclipse on June 10, 2021 as an example. It’s an annular solar eclipse and it’s a member of Saros 147. It’s been causing eclipses since 1624 and will do so until 3049. Here’s what it’s been doing, and will do, in our immediate era—with each event exactly 18 years, 11 days and eight hours apart:
May 31, 2003: annular solar eclipse (Greenland, Iceland, northern Scotland)
June 10, 2021: annular solar eclipse (Canada, Greenland, Russia)
June 21, 2039: annular solar eclipse (Alaska, northern Canada, northern Scandinavia)
You can see the pattern in the dates, above, and the westward drift of the paths of annularity.
It’s exactly the same process for total solar eclipses, which are from a Saros that is currently producing totalities.
In the same way, the totality experienced by 12 million Americans on August 21, 2017’s “Great American Eclipse” was part of Saros 145, so was witnessed 18 years, 11 days and eight hours previously on August 11, 1999 in the U.K. and Europe. Almost precisely the same shadow across Earth will fall on September 2, 2035, but this time on China, Japan and the Pacific Ocean.
So when you’re watching a solar eclipse, remember that it’s part of a pattern that’s far larger than a human lifespan. It repeats through the ages, almost like a mathematical heartbeat as our Sun, Moon and Earth come full circle.