Millions will witness April 8's solar eclipse. Here's what to know about it

On Monday, April 8, a total solar eclipse is set to pass over North America, making its way across Mexico, the United States and Canada.

A total solar eclipse occurs when the moon passes between the sun and earth, completely blocking the face of the sun and creating a breathtaking sight.

Millions of people will be able to witness the total solar eclipse, because they will be in the path of totality. When it happens, the sky can darken as if it were dawn or dusk, and if the weather is favorable, people in the eclipse's path can witness the sun's corona, which is the outer atmosphere typically hidden by the star’s bright face.

The last total eclipse for Americans occurred in 2017, and spanned across the US, crossing from Oregon to South Carolina.

Special event

The upcoming eclipse will cross over much more densely populated areas, as it begins over the South Pacific Ocean, with Mexico being the first location to experience totality at around 11:07am PDT, before passing into Texas, up to Maine, and exiting over Canada, according to NASA.

The space agency estimates that 31.6 million people live in the path of totality this year, compared to 12 million in 2017.

Totality will also last longer than it did in 2017. At that time, it stood at 2 minutes, 42 seconds. This April, it will last about four and a half minutes.

One special element this year could be solar flares on the sun's surface that result in an especially dramatic corona or crown, said Mariel O'Brien, an astronomy educator at the National Air and Space Museum in Washington, DC.

Speaking to TRT World’s Washington correspondent Andy Roesgen, O'Brien said the sun is approaching the end of its typical 11-year cycle, which can make it highly active.

"In 2017, (activity) was at the minimum. I was able to see the eclipse and the corona was very uniform," O'Brien said. "You could see in the corona, just a little bit of a shadow. You might see some more structure than you would see during the solar minimum time."

This cycle is driven by the sun's magnetic field and can be observed through the frequency and intensity of sunspots on the surface. The current solar cycle, which began in 2019, is the 25th cycle recorded since 1755.

Learning from eclipses

By studying solar eclipses, during which the sun’s corona is normally not visible, scientists may be able to better understand the corona's structure and temperature, as well as the effects of the sun on Earth's atmosphere.

O'Brien pointed out that Einstein's theory of general relativity was considered a mere hypothesis until eclipses provided evidence to prove it true in the early 1900s.

In 1915, Einstein's theory introduced a consequence that massive celestial objects, such as the sun, can bend the fabric of spacetime around them, explaining the pull of gravity. According to the scientist, any light that passes through the vicinity of a massive object is also bent along with spacetime.

In 1919, two English astronomers, Arthur Eddington and Frank Dyson, provided the first experimental proof of general relativity. On May 29 that year, they traveled to the island of Príncipe off the west coast of Africa to observe a total solar eclipse.

During the eclipse, scientists took measurements that confirmed Einstein's predictions. The positions of the stars looked different because their light had to travel on the curved space around the sun. This curvature was caused by the sun's gravity, as described by Einstein's theory of relativity.

It's this theory, O’Brien shared, that eventually led to the development of GPS technology.

"It provided observational evidence of that, and if we didn't know about that theory, our cell phones wouldn't work. We wouldn't be able to use GPS. So, that's one example where our everyday lives, even today, are affected by what we learn from an eclipse — the theory of relativity," she said.

Even though eclipses happen all the time, your chance at actually seeing a "total" one is much more rare, she added.

"A total solar eclipse will happen roughly once every 18 months. However, the chance of you seeing one at any one particular place on earth is about once every 375 years. So that's the idea of why they're rare."

Another total solar eclipse won't be visible across the contiguous US until August 2044.

People who have experienced moments of totality say it is almost impossible to describe. Many have even dedicated time to "chase" eclipses, due to the indescribable beauty of the natural occurrence.

According to O'Brien, "It's very beautiful, it's multisensory, and it's very disorienting in a way that's very positive. A writer that I recently read, talked about it being ‘delightfully disorienting’, which I thought was a nice way to put it, because it's an opportunity to see the sky in the color you would not see at any other time."

If you can’t experience the eclipse in person, you can watch it happen online with NASA, which will be live-streaming coverage of the eclipse on April 8 from 1 pm EDT on its website.