What is a hybrid solar eclipse?

A rare hybrid eclipse next happens in 2023. Here’s what that means and how it will affect observers on the ground

What once-a-decade phenomenon next happens on April 20, 2023 in Western Australia, Timor Leste and West Papua? A hybrid solar eclipse (HSE), of course, which is a bit of both a total solar eclipse and an annular solar eclipse.

A hybrid solar eclipse explained

“A hybrid eclipse is one which is annular when the path first touches the Earth, and/or leaves the Earth, but which becomes total for a period in-between,” says Australian astronomer Dave Herald. So how come it becomes total? “The shadow of totality is a cone,” he says. “For a total eclipse, the point of the cone passes below the Earth, and for an annular eclipse, the point of the cone passes above the Earth, never touching it.”

Understanding the ‘shadow cone’

However, hybrid solar eclipses are a bit of both those kinds of solar eclipses. “For a hybrid eclipse the point of the cone passes through the Earth,” says Herald, “For some locations the point is above the Earth’s surface, and the eclipse is seen as annular, and other locations it passes below the surface of the Earth, and the eclipse is seen as total.” On Exmouth Peninsula – the only place in Western Australia where the moon’s shadow makes land on April 20, 2023, as well as in Timor Leste and West Papua – observers will witness a total solar eclipse.

Why is an HSE rare?

The difference between a shadow cone passing above and below Earth is slight, making hybrid eclipses unlikely. “Hybrid eclipses are rare because the range for the location of the point of the cone is quite small,” says Herald.

The three HSE experiences

All this means there are three forms of eclipse experience during a hybrid solar eclipse, depending on exactly where you stand. The first is a true annular eclipse, with an unbroken ring of light, and the third is a true total eclipse. However the scenario in the middle – viewable at the transitional point between an annular and a total eclipse – is the most interesting (and least seen). “It’s a broken-annular eclipse, where the ring of light is broken by lunar mountains,” explains Herald. “It is effectively a series of Baily’s beads around the complete circumference of the moon (where) the number of Baily’s beads increases, then decreases, as one moves from the point of full annularity to the point of full totality.”

Hybrid solar eclipses are relatively rare. After 2023 there’s a gap of eight years until the next one on November 14, 2031. Beyond that, two come along in quick succession in 2049 and 2050. However, for eclipse-chasers heading to the Path of Totality on April 20, 2023, it will be just a normal total solar eclipse … if there is such a thing!

Pic credit: Pixabay