A hybrid solar eclipse, the rare celestial event, occurred with the greatest totality—the Moon fully covering the Sun—on April 20, 2023 (7.06 a.m. IST till 12.29 p.m. IST).
It was observed in the region of the Indian and Pacific Oceans, specifically western Australia, East Timor, and eastern Indonesia. These parts witnessed the eclipse transition from annular to total before transitioning back to annular. The ‘ring of fire’ was visible for a few seconds. Some other places in the region also experienced a partial eclipse (the most common eclipse in which the Moon blocks out just a part of the Sun sending a shadow, the penumbra, across the Earth). The hybrid solar eclipse was not visible in India.
The first of its kind in nearly 10 years, the hybrid solar eclipse (also called annular-total eclipse) combines the characteristics of both annular and total solar eclipses.
The total, annular, and hybrid solar eclipses occur only when the Sun-Moon-Earth alignment is perfect and the observer is on the centre line of the eclipse. When any of these two conditions is absent, then only a partial eclipse of the Sun can be seen.
Types of Solar Eclipses
There are four types of solar eclipses, which are as follows:
A total solar eclipse occurs when in a Sun-Moon-Earth alignment, the Moon comes directly across the face of the Sun and has a slightly larger apparent diameter than the Sun. The Moon then fully obscures the solar disc (the Moon appears to be of the same size as the Sun) and a total eclipse is seen. The Moon’s umbra—its central and darkest shadow—causes a brief darkening of the sky as the Moon blocks nearly all of the Sun’s disc from view except for its outer fiery atmosphere. The spectacular sight of the solar corona, the Sun’s pale white outer atmosphere, can be viewed with the naked eye.
An annular solar eclipse occurs when the Moon’s apparent size is slightly smaller than the Sun’s. The Moon’s shadow appears smaller on the Sun and leaves an outer circle of light (ring of fire) from the Sun visible from within the lunar shadow called the antumbra that reaches the Earth. The Moon’s antumbra exists only when the light source (the Sun in this case) has a larger diameter than the object (the Moon).
A partial solar eclipse occurs when the Moon passes between the Sun and the Earth but the Sun-Moon-Earth alignment is not perfect. Only a part of the Sun appears to be covered and the Sun assumes a crescent shape. It is visible to those who are outside the area covered by the Moon’s inner shadow during a total or annular solar eclipse.
The rare hybrid solar eclipse takes place when the eclipse changes from annular to total or vice versa along the centreline path of the eclipse. Over 90 per cent of hybrid eclipses begin as annular, become total and stay so for the most part, and then revert to annular (annular-total-annular) at the end of the eclipse path.
For a hybrid eclipse to happen, the Moon has to be at just at the right distance from the Earth so that both the umbral and antumbral shadows reach the planet. The eclipse occurs when the tip of the Moon’s dark umbral shadow touches the surface of the Earth at some points but falls short of the surface at one end or at both the ends of the eclipse centreline. In an annular-total-annular eclipse, at the beginning and end of the eclipse track, the Earth curves and the umbra does not quite reach the planet (so annular) but the planet’s curvature causes the middle section of the eclipse track to be nearer to the umbra (so totality). The Moon’s distance from the Earth determines the shadow projected onto the Earth’s surface: from the faint penumbra of a partial solar eclipse to the deep and dark umbra of totality and the antumbra—a kind of half-shadow—of annularity.
In a hybrid solar eclipse, when the Moon’s umbral and antumbral shadows traverse the Earth, the eclipse appears annular and total along different sections of its path. Annularity or totality is seen at different times depending on where the observer is located (an observer from any one point on the Earth cannot see both annular and total eclipse in the same interval of time).
As the occurrence of a hybrid solar eclipse depends on the curvature of the Earth and the Moon’s distance from the Earth, it is rarely seen. It is believed that less than five per cent of all solar eclipses are hybrid.
A hybrid solar eclipse occurs only a few times in a century. Only seven hybrid solar eclipses are expected to occur in the 21st century. The last one was on November 3, 2013 and the next one may occur on November 14, 2031. In the next century, a hybrid solar eclipse is expected to occur on March 23, 2164.
© Spectrum Books Pvt. Ltd.