The last solar eclipse of the decade – and the only annular solar eclipse of the year – took place yesterday, in a fitting send-off for the decade. If you missed it, we have good news for you: you can watch it right here, in the video below.
Annular solar eclipses, like total solar eclipses, occur when the Moon passes in front of the Sun. However, the Moon doesn’t totally cover the Sun during annular solar eclipses, leaving behind an annulus, or bright ring.
Eclipses occur because the Moon’s orbit around the Earth is tilted with respect to the ecliptic plane, the plane of the Earth’s orbit around the Sun. The Moon will appear to pass in front of the Sun if the new Moon phase, when the Moon is on the day side of the Earth, occurs around the time that the Moon crosses the ecliptic plane.
During total solar eclipses, the Moon completely covers the Sun, leaving behind just the glow of the solar atmosphere, or corona. But annular solar eclipses, when the Moon can’t completely cover the Sun, occur because the distances between celestial objects change due to the eccentricity of their orbits. At its closest, or perihelion, the Earth’s orbit takes it approximately 91 million miles from the Sun in January. The Sun looks largest in the sky during perihelion. At its furthest, or aphelion, the Earth is around 94.5 million miles from the Sun, and the Sun looks its smallest in the sky. Meanwhile, the Moon ranges from 225,000 miles away at its closest, or perigee, to 252,000 miles at its furthest, or apogee.
EarthSky.org reports that during this year’s annular eclipse, the Moon was at approximately its average distance to the Earth, while the Sun was near its closest. An average-looking Moon isn’t enough to totally cover an especially big Sun.
This eclipse was the only annular eclipse of the year, though a total solar eclipse occurred on 2 July 2019, which passed over South America including one of the United States’ observatories in Chile. Another annular eclipse will occur on 21 June next year, and will also be mostly visible from the Eastern hemisphere.
Featured image: Kevin Baird (Wikimedia Commons)