Why a hybrid solar eclipse is so rare

A “hybrid” solar eclipse is set to darken the skies above Australia and Indonesia on Thursday in a rare occurrence.

The eclipse is due to will start at 9:34 p.m. ET on April 19 and end around 5 hours later at 2:59 a.m., according to timeanddate.com.

A hybrid eclipse, also known as annular-total eclipses, “beaded” solar eclipses, or “broken” annular eclipses, is a mixture of two other types of eclipses: an annular eclipse and a total eclipse.

What’s A Solar Eclipse?

Solar eclipses occur when the moon passes between the Earth and the sun, blocking out the light of the star and sending its shadow across the Earth. A total eclipse is what happens when the moon perfectly covers the sun, leaving only the tendrils of the sun’s corona visible around the edges of the black disc.

What’s an Annular Eclipse?

An annular eclipse is similar, but occurs when the moon is slightly smaller in the sky due to being further away from the Earth, leaving more of the sun visible around the circumference in a “ring of fire”, Space.com explains.

What’s a Hybrid Solar Eclipse?

A hybrid solar eclipse is a rare combination of the two, occurring in only 3.1 percent of solar eclipses in the 21st century, and can be seen transitioning between the two types over the course of the eclipse. NASA data shows that in the 5,000 years between 2000 BCE to 3000 CE, only 4.8 percent of solar eclipses have been or will be hybrid eclipses.

These are rare because of the angle of the moon’s shadow on the Earth’s curved surface and how when the moon is further away from the Earth, the eclipse can appear annular at some points on its path, and total at others. The area of the total eclipse occurs during the middle of the shadow’s path, due to that area of the Earth’s surface being ever so slightly closer to the moon, according to Space.com.

“Roughly speaking, the geometry has to be such that a total eclipse happens,” Amitabh Virmani, an associate professor of astrophysics at Chennai Mathematical Institute in India, told Newsweek. “On top of that, if the geometry is such that it is barely total (that is, the angular sizes of the moon and the sun are almost matching) at one location, then it is possible to picture that at a nearby location the moon’s angular size is a tiny bit smaller so we get an annular solar eclipse there. Such an arrangement is rare, and hence these eclipses are rare.”

In Thursday’s eclipse, the portions of its path near sunrise and sunset will appear annular, beginning over the Indian Ocean, transitioning to a total eclipse over the ocean and appearing as a total eclipse over western Australia, before changing back to appearing annular over the South Pacific.

Skygazers are urged to always wear appropriate eye protection when watching the eclipse, or else risk damage to their eyes. For those outside of the eclipse’s path, the Gravity Discovery Centre & Observatory near Perth in Australia will be hosting a livestream of the eclipse on YouTube from 10 p.m. ET on April 19.

The U.S. will next experience its own hybrid solar eclipse on November 14, 2031, but there are many others to see between now and then.

Do you have a tip on a science story that Newsweek should be covering? Do you have a question about hybrid solar eclipses? Let us know via science@newsweek.com.