What to expect during April’s total solar eclipse

By Ashley Strickland, CNN

(CNN) — Sky-gazers across North America are in for a treat on April 8 when a total solar eclipse will pass over Mexico, the United States and Canada.

The event will be visible to millions — including 32 million people in the US alone — who live along the route the moon’s shadow will travel during the eclipse, known as the path of totality. For those in the areas experiencing totality, the moon will appear to completely cover the sun. Those along the very center line of the path will see an eclipse that lasts between 3½ and 4 minutes, according to NASA.

The next total solar eclipse won’t be visible across the contiguous United States again until August 2044. (It’s been more than six years since the “Great American Eclipse” of 2017.) And an annular eclipse won’t appear across this part of the world again until 2046.

Here’s everything you need to know about the upcoming eclipse.

What is a total solar eclipse?

A total solar eclipse occurs when the moon passes between Earth and the sun, completely blocking the sun’s face.

Those within the path of totality, or locations where the moon’s shadow will completely cover the sun, will see a total solar eclipse. People outside the path of totality will still be able to see a partial solar eclipse, where the moon only blocks part of the sun’s face.

During a total solar eclipse, the sky will darken as it would at dawn or dusk, and there are several stages of the eclipse for sky-gazers to anticipate.

The moon doesn’t suddenly appear between Earth and the sun — the event begins with a partial eclipse in which it looks like the moon is taking a “bite” out of the sun, causing the sun to resemble a crescent. Depending on your location, the partial eclipse can last between 70 and 80 minutes, according to NASA.

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 in a phenomenon called Baily’s beads.

As totality nears, Baily’s beads will quickly disappear until a single point of light remains, resembling a glistening giant diamond ring.

The diamond ring will disappear when totality arrives, and there is no longer any sign of direct sunlight. Bright stars or planets may shine in the dark sky, and the air temperature will drop as the sun disappears. The sudden darkness causes animals to grow quiet.

The chromosphere, or part of the sun’s atmosphere, may glow in a thin pink circle around the moon during totality, while the sun’s hot outer atmosphere, or corona, will appear as white light.

As the moon continues its trek across the sun’s face, the diamond ring and Baily’s beads and the partial solar eclipse will appear on the opposite side of the moon until the sun fully reappears.

Where can I see the eclipse?

The total solar eclipse will be visible in parts of Mexico, Canada and more than 10 US states, while a crescent-shaped partial solar eclipse is expected to appear in 49 states — weather permitting.

The eclipse will first appear over the South Pacific Ocean and begin its journey across North America. Mexico’s Pacific coast is the first point of totality on the path, expected at 11:07 a.m. PT (2:07 p.m. ET).

The pathway will continue across Texas, Oklahoma, Arkansas, Missouri, Illinois, Kentucky, Indiana, Ohio, Pennsylvania, New York, Vermont, New Hampshire and Maine. Then, it will cross over Canada in southern Ontario, Quebec, New Brunswick, Prince Edward Island and Nova Scotia, ending on the Atlantic coast of Newfoundland at 5:16 p.m. (3:46 p.m. ET).

Use our interactive map to determine what the eclipse will look like from your viewing location.

How do I safely view the eclipse?

The only time it’s safe to view the sun without eye protection is during the “totality” of a total solar eclipse, or the brief moments when the moon completely blocks the light of the sun and no sunlight is visible, according to NASA.

Otherwise, wear certified ISO 12312-2 compliant eclipse glasses or use a handheld solar viewer before and after totality, and at all times during a partial eclipse.
Separately, you can observe the sun with a telescope, binoculars or camera that has a special solar filter on the front, which acts the same way eclipse glasses would.

Directly staring at the sun can result in blindness or disrupted vision. During the 2017 total solar eclipse, a young woman was diagnosed with solar retinopathy, retinal damage from exposure to solar radiation, in both eyes after viewing the eclipse with what doctors believed were eclipse glasses not held to the safety standard. There is no treatment for solar retinopathy. It can improve or worsen, but it is a permanent condition.

Sunglasses won’t work in place of eclipse glasses or solar viewers, which are 100,000 times darker and held to an international safety standard.

The lenses of solar eclipse glasses are made of black polymer, or resin infused with carbon particles, which blocks nearly all visible, infrared and ultraviolet light, according to The Planetary Society. Sunglasses don’t block infrared radiation.

For safe manufacturers and resellers of eclipse glasses and filters for optical devices, including cameras and smartphones, check out the list curated by the American Astronomical Society.

Put on your eclipse glasses before looking up and remember to turn away from the sun before you remove them again. Always keep an eye on any children wearing eclipse glasses to make sure they don’t remove them while looking at the sun.

If you normally wear eyeglasses, keep them on and put eclipse glasses over them or hold a handheld viewer in front of them, according to the American Astronomical Society.

Don’t look at the sun through any unfiltered optical device — camera lens, telescope, binoculars — while wearing eclipse glasses or using a handheld solar viewer, according to NASA.

Solar rays can still burn through the filter on the glasses or viewer, given how concentrated they can be through an optical device, and can cause severe eye damage.

If you bought eclipse glasses to see the “ring of fire,” save your eclipse glasses and viewers for the total solar eclipse in April by storing them at room temperature in an envelope or their original packaging to avoid scratches.

What can we learn from eclipses

Eclipses afford scientists the opportunity to study the sun and how it interacts with Earth in unique ways, and NASA has selected several projects to fund during the total solar eclipse.

“Scientists have long used solar eclipses to make scientific discoveries,” said Kelly Korreck, program scientist at NASA, in a statement. “They have helped us make the first detection of helium, have given us evidence for the theory of general relativity, and allowed us to better understand the Sun’s influence on Earth’s upper atmosphere.”

One project will rely on NASA’s high-altitude research planes to take images of the eclipse from 50,000 feet (15,240 meters) above Earth’s surface to capture previously unseen details in the sun’s corona. The images could also help scientists search for asteroids that orbit near the sun.

Amateur radio operators will try an experiment during both the annular and total solar eclipses to see how these phenomena change the way radio waves travel. Operators in different locations will record the strength of their signals and how far they travel. Scientists are interested in tracking this distance because the sun directly influences Earth’s upper atmosphere, or ionosphere, which allows radio communications to travel farther. But when the moon blocks the sun, that can change.

Scientists and citizen scientists alike are planning to observe the sun’s most active regions as the moon passes over them using the Goldstone Apple Valley Radio Telescope during both eclipses.

The sun is currently approaching solar maximum later this year, and scientists are eager to capture this peak of activity through a variety of observations that can only occur during eclipses.

Clarification: This story has been updated to clarify what those in the path of totality will see.

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