When the total solar eclipse traces a path across Mexico, the United States and Canada on April 8, spectators can anticipate a multitude of awe-inspiring moments.
During a total solar eclipse, the moon completely blocks the face of the sun for a brief period known as totality — and 32 million people in the US who are located along the 115-mile-wide (185-kilometer-wide) path of totality for April’s event will have a chance to enjoy this full expression of the celestial spectacle.
It’s worth taking some time to stop and take in this historic celestial event because a total solar eclipse won’t be visible across the contiguous US again until August 2044 and an annular eclipse, in which the moon can’t completely block the sun, won’t appear across this part of the world again until 2046.
“Until you’ve actually seen (a total eclipse), it’s almost impossible to describe,” said Dr. John Mulchaey, Carnegie Institution for Science’s deputy for science and the director and Crawford H. Greenewalt Chair of the Carnegie Observatories. “When you see totality, you can see how it’s had such a huge impact on humans through thousands of years. It’s one of the most beautiful things most people will ever experience.”
But the phases surrounding totality — including a couple phenomena stunning enough to have earned their own names — are pretty memorable, too, eclipse experts say. Here’s what to look out for.
What to watch for during the eclipse
The moon doesn’t suddenly appear between Earth and the sun — the event begins with a partial eclipse, in which the moon appears to take a “bite” out of the sun. Depending on your location, the partial eclipse can last between 70 and 80 minutes, according to NASA.
For those living outside of the path of totality, a crescent-shaped partial eclipse, rather than a total eclipse, will be the main event. Within the path, the partial eclipse is the longest phase, but as the time for totality nears, look for changes in the sky’s appearance.
“About 15 to 20 minutes before totality, the sky starts getting this really weird gloomy color,” Mulchaey said. “It’s almost like a gray because the sun’s way high in the sky, but it’s almost entirely blocked out. It’s not like twilight, sunset or sunrise when (the sun is) low in the sky. It’s above you. And all of a sudden, you’re losing most of the sun’s light, and it feels very weird.”
The eerily darkening sky is a cue for skywatchers that the stellar show is about to begin. Just make sure you have eclipse glasses handy to safely view the sun before the event gets underway. Two breathtaking phases occur within the final moments before totality, Mulchaey said.
When the moon begins to cross in front of the sun, the star’s rays will shine around valleys on the moon’s horizon, creating glowing drops of light around the moon called Baily’s beads. The phenomenon was named for English astronomer Francis Baily, who noted them during an annular eclipse on May 15, 1836.