The last solar eclipse of the decade—and the only annular solar eclipse of the year—will be visible in Europe, Asia, Australia, and Africa starting just a few hours after this article’s publication.
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.
The partial eclipse will become visible from the Indian Ocean and South Asia on December 26 at 02:29:53 UTC, or December 25 at 9:29:53 p.m. EST, according to TimeAndDate.com. The maximum eclipse will first become visible over the southeastern Arabian Peninsula just after sunrise on December 26 at 03:34:33 UTC (December 25, 10:34:33 p.m. EST). The path of greatest eclipse will then travel over the Indian Ocean, southern India and Sri Lanka, Indonesia, and the Philippines.
If you’ve got nothing to do tonight, you can watch the Slooh livestream below, which begins at 10:00 p.m. EST.
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 will be at approximately its average distance to the Earth, while the Sun will be near its closest. An average-looking Moon isn’t enough to totally cover an especially big Sun.
This eclipse is the only annular eclipse of the year, though a total solar eclipse occurred on July 2, 2019, which passed over South America including one of the United States’ observatories in Chile. Another annular eclipse will occur on June 21 next year, and will also be mostly visible from the Eastern hemisphere.