A rare celestial event is set to occur on April 20th – a hybrid solar eclipse. This phenomenon is an infrequent occurrence, happening only once a decade on average. It is a unique combination of the three types of solar eclipses that can take place – total, partial, and annular. This is because the Sun, Earth, and Moon must be in very specific positions for a hybrid solar eclipse to occur. In fact, of the 224 eclipses in the 21st century, only 7 are hybrid, accounting for just 3.1% of all solar eclipses. If you have the opportunity to witness this event, you should not miss it.

But what’s a hybrid solar eclipse?

A Hybrid Solar Eclipse is Coming: A Once-in-a-Decade Event You Won't Forget! 1
3 Shadows, 3 Eclipses | Credit: Time and Date

To understand what a hybrid eclipse is, you need to understand the three areas of the shadow that the Moon casts on Earth during a solar eclipse. The first is the umbra, the dark central portion that causes a total solar eclipse. If you are in the Moon’s umbra, you will see that the Moon appears slightly larger than the Sun, completely covering it.

A Hybrid Solar Eclipse is Coming: A Once-in-a-Decade Event You Won't Forget! 2

The second is the penumbra, the lighter outer part of the shadow that creates a partial solar eclipse. If you are in the penumbra, you will see that the Moon obscures only a part of the Sun’s disk. Finally, we have the antumbra, a half-shadow that begins where the umbra ends, creating an annular solar eclipse. During this type of eclipse, the Moon appears slightly smaller than the Sun, so the edge of the Sun’s disk remains visible around the Moon.

Hybrid solar eclipses involve all three areas of the Moon’s shadow and combine all three types of solar eclipses. The type of solar eclipse that’s visible to observers depends on their location along the central eclipse path. This may not sound very interesting, but once you understand that it’s all a play of Earth’s curvature, it will surprise you.

Earth’s curvature plays a critical role in a hybrid solar eclipse

A Hybrid Solar Eclipse is Coming: A Once-in-a-Decade Event You Won't Forget! 3
Credit: Time and Date

Let’s go back to the Moon’s shadow cast upon Earth during an eclipse. Because the Moon is smaller than the Sun, both its umbra and its antumbra are V-shaped. The diameter of the umbra decreases with the growing distance from the Moon. Where the umbra ends, at the tip of the V, the antumbra starts. This part of the shadow increases in diameter as we move away from the Moon. Together, both shadows look a bit like an hourglass if viewed from the side.

The location where the umbra transitions into the antumbra marks the spot where, if you look at the Sun and the Moon, the apparent sizes of both celestial bodies are exactly equal. If you move towards the Moon from that spot, you enter the umbra and see a total solar eclipse; if you move away from the Moon, you enter antumbral territory, so the Moon begins to appear smaller than the Sun, creating an annular eclipse.

Now here comes the interesting part. The distance to the Moon depends on your location on Earth. The Earth-Moon distance is the smallest in the spot facing the Moon directly. Since the Moon’s umbra only covers a certain distance before turning into the antumbra, the Earth’s curvature can bridge the distance between the 2 shadows. So what begins as an annular solar eclipse can turn into a total solar eclipse and back to an annular again. However, sometimes, the eclipse does not turn annular again.

A mathematical coincidence

The reason why hybrid solar eclipses are so rare is that each of the three celestial bodies need to be at a specific position for it happen. Since the spectrum of distances required for a hybrid eclipse is so narrow, most eclipse configurations are unsuitable for this type of eclipse. In mathematical terms, if you divide the distance between the Sun and the Earth during the eclipse by the distance between the Moon and the Earth, the result must be a number very close to 400 for a hybrid solar eclipse to occur.

Hybrid Solar Eclipse of April 2023

Hybrid Solar Eclipse 2023 Map
The path of the hybrid solar eclipse on April 19-20, 2023 | ©Vito Technology, Inc.

The upcoming hybrid solar eclipse will take place on April 20 and will be visible from western Australia, East Timor, and eastern Indonesia. The entire eclipse will last about five-and-a-half hours. It will transition from annular to a total and back again at two specific points, but both are at remote locations at sea. 

Just before and just after totality, a big display of Baily’s beads will be visible. Baily’s beads are the last rays of sunlight that can be seen streaming through the valleys of the moon just before totality. They can also be seen as totality ends. During a hybrid solar eclipse, the displays of Baily’s beads are longer because the moon is almost precisely the same apparent size as the Sun.

A Hybrid Solar Eclipse is Coming: A Once-in-a-Decade Event You Won't Forget! 4
This image highlights Baily’s Beads, a feature of total solar eclipses that are visible at the very beginning and the very end of totality. It’s composed of a series of images taken during a total solar eclipse visible from ESO’s La Silla Observatory on 2 July 2019.

Be Careful!

Also, keep in mind that it is not safe to look at a solar eclipse with the naked eye or through a telescope without proper protective measures. The reason for this is that the intense light and radiation from the Sun can cause severe and permanent damage to our eyes. One way to safely view a solar eclipse is by using special eclipse glasses or solar filters that are designed to block out harmful rays.

Following the hybrid solar eclipse, skywatchers can view the next solar eclipse occurring on October 14, which will be an annular eclipse visible from the Americas. Stay updated on the most significant astronomical events in 2023 by keeping an eye on our astronomy calendar, which covers all the important celestial phenomena throughout the month.

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