Solar Eclipse: When and Where Will it be Visible and How Long Will it Last?

On June 21, a "ring of fire" solar eclipse will grace the skies over some parts of the planet.

Unfortunately, the event—known as an "annular" solar eclipse—won't be visible in the Americas. The best views will be reserved for people living across a sliver of central Africa and south Asia, although a much wider region will experience a partial eclipse.

Solar eclipses—of which there are four main types—occur when a new moon passes in front of the sun, blocking starlight and bathing parts of the Earth in shadow.

Perhaps the most well-known type of solar eclipse is a total solar eclipse, such as the one that was visible from the U.S. in August 2017, during which the moon completely covers the sun's bright face.

"[This causes] daylight to fade to deep twilight, allowing us to see the magnificent solar corona—the [star's] ethereal outer atmosphere, which is always there but is usually invisible due to the overwhelmingly brighter glare from the sun's face," Rick Fienberg, a spokesperson for the American Astronomical Society, told Newsweek.

However, an annular eclipse—named after the Latin word for ring, "annulus"—is slightly different. In these cases, the moon is not quite big enough to cover the entirety of the sun's bright face at maximum eclipse. This results in the appearance of a brilliant ring of sunlight—the characteristic "ring of fire"—that is momentarily visible around the silhouetted moon from some regions of the Earth.

"The landscape darkens a bit, but not nearly as much as during a total solar eclipse, and you can't see the solar corona," Fienberg said.

During total and annular solar eclipses, the moon only casts a shadow across small portions of the Earth.

"This shadow is never more than about 150 miles wide—it's usually only tens of miles wide—and it sweeps across Earth's surface faster than a supersonic jet. Only if you're within that narrow path when the shadow comes by—and only if the weather cooperates—will you see the total or annular eclipse; in a much larger area outside this path you'll see a partial eclipse, that is, the moon will cover only part of the sun's bright face, looking like it took a 'bite' out of the sun," Fienberg said.

For the June 21 eclipse, the path of annularity—where the ring of fire will be visible—spans two continents and 14 countries. The path will begin in central Africa, and sweep through East Africa, south Asia—including northern India and China—before ending in the Pacific Ocean.

At its widest in West Africa, the path will measure only about 53 miles wide. This figure drops to around 13 miles wide at the location of maximum eclipse in Uttrakhand, India. Here, the ring of fire will only be visible for around 38 seconds, according to timeanddate.com.

Across a much wider region either side of this narrow path of annularity will be a partial eclipse, including in parts of southern and eastern Europe, most of Asia, most of Africa, the very north of Australia and large chunks of the Pacific and Indian oceans. The Americas will miss out on the annular eclipse because the event is set to finish before the sun rises.

"Obviously an eclipse occurs during daytime, when the sun is up, so if it occurs on one side of the planet, the other side misses out because it's nighttime," Fienberg said.

In total, the event will last around six hours if you measure from the moment that a partial eclipse begins in the first location and ends in the final location—3:45 a.m. and 9:34 a.m. UTC respectively, or 11:45 p.m. EDT (June 20) and 5:34 a.m. EDT.

annular solar eclipse
Stock image: An annular solar eclipse in the skies above Saudi Arabia in 2019. iStock

However, the full annular eclipse will only be visible from the first location from 4:47 a.m. UTC (12:47 a.m. EDT) and will end in the last location at 8:32 a.m. UTC (4:32 a.m. EDT.) Meanwhile, maximum eclipse will take place at 6:40 a.m. UTC (2:40 a.m. EDT.)

Annular solar eclipses only take place when a new moon is located at its farthest point from Earth, or apogee. But why do we sometimes get total solar eclipses and other times annular ones?

"Earth orbits the sun in an ellipse, not a perfect circle, and the moon orbits Earth in an ellipse too, so the distances between the three bodies change constantly," Fienberg said. "The closer or farther the sun or moon, the bigger or smaller they appear in the sky (though not by so much that you'd notice; the effect is about 3 percent for the sun and 14 percent for the Moon)."

"We get total solar eclipses when the sun is farther/smaller than average and the moon is closer/bigger than average, and we get annular solar eclipses when the sun is closer/bigger than average and the moon is farther/smaller than average," he said.

If you happen to be in a region where you can witness this year's annular eclipse, remember that you should never look directly at the event without eye protection.