by Sign up for CNN’s Wonder Theory science newsletter. Explore the universe with news on exciting discoveries, scientific advances and more.
When the total solar eclipse traces a path across Mexico, the United States and Canada on April 8, viewers can expect many inspiring moments.
During a total solar eclipse, the moon completely blocks the face of the sun for a brief period called totality — and a total of 32 million people in the US are located along the 115-mile-wide (185-kilometer-wide) path. the April event will have the opportunity to enjoy this full display of heavenly spectacles.
It’s worth taking some time to stop this historic celestial event because a total solar eclipse won’t be visible across the contiguous US again until August 2044 and there won’t be an annular eclipse, when the moon can’t block the sun completely, to be seen. They will not be seen across this part of the world again until 2046.
“Until you see (a total eclipse), it’s almost impossible to describe,” said Dr. John Mulchaey, science representative of the Carnegie Institute for Science and director and Crawford H. Greenewalt Chairman of the Carnegie Observatory. “When you see the whole, you can see how it has had such an impact on people for thousands of years. It’s one of the most beautiful things most people will ever experience.”
But the stages of totality – including a few stunning phenomena that deserve their own names – are quite memorable, too, say eclipse experts. Here’s what to look out for.
What to watch during the eclipse
The moon suddenly becomes invisible between the Earth and the sun – the event begins with a partial eclipse, and the moon seems to take a “bite” out of the sun. Depending on your location, the partial eclipse may last between 70 and 80 minutes, according to NASA.
For those living outside the path of totality, a partial crescent-shaped eclipse, rather than a total eclipse, is the main event.
Within the path, the partial eclipse is the longest phase, but as the time for totality approaches, look for changes in the appearance of the sky.
“About 15 to 20 minutes before totality, the sky starts to get this really weird dark color,” Mulchaey said. “It’s almost like gray because the sun is high in the sky, but it’s almost completely blocked. It is not like twilight, sunset or sunrise when (the sun is) low in the sky. It is above you. And suddenly, you’re losing most of the sunlight, and it feels very strange.”
The cloudless sky is a sign to sky watchers that the spectacular show is about to begin. Make sure you have eclipse glasses to see the sun safely before the event begins.
Two remarkable 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 blobs of moonlight around the moon called Baily’s beads. The phenomenon was named for the English astronomer Francis Baily, who observed them during the annular eclipse of 15 May 1836.
As totality approaches, Baily’s beads will quickly disappear and make way for the “diamond ring,” nicknamed for how it looks when a single point of light remains — like a giant glistening diamond ring.
Both of these steps last less than a minute, Mulchaey said.
Then it’s time for the whole.
Prepare for full
The total phase of the April 8 eclipse is expected to last twice as long as it did in 2017 because the moon is now closer to the sun. Those square on the path’s centerline will see a total eclipse lasting 3½ to 4 minutes, according to NASA.
“All of a sudden, the whole thing happens, and the corona shows up,” Mulchaey said. “Even though it’s dark outside, it’s somehow glorious.”
The corona is the ultra-hot outer atmosphere of the sun, which emits a glow that can be seen around the moon during the eclipse. Normally, the corona is difficult to see because the surface of the sun is much brighter. During the total eclipse, the corona will look like white streams of light, according to NASA.
During the 2017 eclipse, the sun was approaching solar minimum, or the quiet phase of our star’s 11-year cycle of activity. Now, the sun is approaching solar maximum, when the sun is most active, Mulchaey said. The corona will likely appear brighter and fuller, and there may be a chance to see flared loops of solar activity like streams within the corona during the eclipse.
Viewers may be able to see a region of the sun’s atmosphere called the chromosphere, which will appear as a thin pink circle around the moon.
Bright stars or planets like Venus may shine in the dark sky, and the air temperature will drop as the sun disappears. The sudden darkness also causes animals to behave in unusual ways.
“We may start to see nocturnal behaviour, like crickets chirping or bats emerging, and animals stopping daytime behaviour, like birds roosting or flying insects landing,” said Dr. Andrew Farnsworth, visiting scientist at the Cornell Laboratory of Ornithology.
After total completion, the diamond ring and Baily’s beads will be visible again briefly before the partial eclipse returns as the moon moves slowly across the sun.
Why do we have eclipses on Earth
Only six years have passed since the total eclipse crossed the United States, the path of the April 8 eclipse is very different, trekking from the west to the east.
On average, an eclipse happens in the same place every 375 years, Mulchaey said.
And we are living at the right time to enjoy a total eclipse view on Earth, he said.
Although eclipses occur throughout the solar system, none of them are exactly like the ones experienced in our lifetime.
The moon is about 400 times smaller than the sun, but the moon is also about 400 times closer to Earth than the sun, creating a “beautiful coincidence” that results from an eclipse when the three celestial bodies align, which Mulchaey said.
This alignment is called syzygy, or when three objects line up in space.
In the distant past, the moon was much closer to Earth, which means that the whole thing was probably not visible as it is now. And within another 60 million years or so, the moon will be so far away that it will never cover the sun, making this a rare moment in time, Mulchaey said.
For more CNN news and newsletters create an account at CNN.com
