Frontier Adventure

Rare Hybrid Annular-Total Solar Eclipse Set for April 20th

The first solar eclipse of 2023 will span Australia and southeast Asia into the Pacific Ocean region.

Mark your calendars. The first eclipse season of 2023 is about to begin on Thursday, April, 20th, with a rare hybrid annular-total solar eclipse.

Solar Eclipse Primer

Eclipses occur when the Moon passes between the Earth and the Sun, casting its shadow across the surface of the planet. The Moon’s path is inclined five degrees relative to the ecliptic plane, and misses the Sun on most passes. Otherwise, we’d see two eclipses—one lunar and one solar—per month. For an eclipse season to occur, New and Full Moon need to fall very near an intersection node of the Moon’s orbit and the ecliptic. This happens about twice a year.

Total eclipses occur when the Moon completely covers the Sun, plunging those standing in the shadow of the Moon into an eerie darkness and revealing the pearly white solar corona. This is the kind of eclipse most folks will get on a plane and head to an exotic location for. Though we often marvel at how the Moon seems to be a great fit versus the Sun as seen from the Earth, this isn’t always the case. If New Moon is headed towards apogee and the Sun is a few months within perihelion, the inner umbral shadow fails to reach the surface of the Earth, and an annular eclipse occurs. Observers are then treated to a brilliant ‘ring of fire’ eclipse.

Animation for the April 20th eclipse. Credit: NASA/GSFC.AT Sinclair.

Bizarre Hybrid Solar Eclipse

But something stranger still happens on April 20th. The Moon’s umbral shadow barely brushes the Earth on one part of the track, only to liftoff again on the other. This is the hybrid portion of the eclipse, which transitions from a broken annular, to totality, then back to annular again.

Types of solar eclipses: total (left), annular (center) and partial (right). Credit: NASA/Joseph Matus/Bill Dunford/Bill Ingalls.

The 49-kilometer wide path touches down at sunrise over the Indian Ocean. The eclipse only brushes land briefly at three points. First landfall occurs over the extreme northwestern tip of Australia along the Ningaloo Coast and the tiny town of Exmouth. The shadow then crosses the Timor Sea and touches the eastern tip of the island nation of East Timor near the capital of Dili, and then crosses a scattering of Indonesian islands including Kisar, the Schouten Islands and Western New Guinea.

Circumstances with times in UT, and partial eclipse percentages for the April 20th hybrid eclipse. Credit: Michael Zeiler.

Maximum duration for totality is only 1 minute and 16 seconds, just south of the Indonesian island of East Timor in the Timor Sea.

Rare (and Remote) Event

How rare is a hybrid eclipse? Well, there are only seven hybrid eclipses in the 21st century, or 3.1% of solar eclipses overall. Annulars are actually more common than totals in the current epoch, and will continue to become even more so over the next few hundred million years as the Moon slowly recedes from the Earth, until all central solar eclipses are elusively annular.

“The April 20, 2023 hybrid solar eclipse is notable in that it is longer in duration than most annular-totals, and is the
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