On June 10, millions of people across large parts of the Northern Hemisphere will be able to witness the majesty of a solar eclipse. Depending on where you live, you may see either a stunning ring of fire known as an annular eclipse or a partial solar eclipse, with a portion of the sun covered by the moon.
For many observers in the northeastern United States, the sun will already be partially eclipsed as it appears above the horizon, creating a crescent sunrise.
If local conditions are just right, some viewers in areas including New York, New Jersey, and Massachusetts may be lucky enough to experience a rare Devil’s Horns sunrise. This spooky sight occurs when two ends of the sun’s visible crescent poke above the eastern horizon, appearing to float like a pair of fiery curved horns.
Meanwhile, any sky-watchers in a narrow path across remote parts of northern Canada and the Arctic will be treated to a full annular eclipse, when the edges of the sun will shine around the perimeter of the darkened lunar disk.
Flavors of solar eclipse
A solar eclipse occurs when Earth, the moon, and the sun line up perfectly so that the moon blocks the sun and casts its shadow on our planet. However, the moon follows an elliptical orbit around Earth, meaning sometimes it is closer to our planet and sometimes it is farther away, causing it to appear either bigger or smaller in the sky.
A total solar eclipse, such as the Great American Eclipse in 2017, happens when the moon is close enough to Earth to completely cover the sun. Annular eclipses occur when the moon is farther away and so appears smaller than the visible disk of the sun. Then it does not cover up our star completely but leaves a shining ring surrounding the dark face of the moon.
The first of two solar eclipses in 2021, this week’s main event will be visible in some Arctic regions just after local sunrise and through the morning hours. The annular eclipse will first appear for viewers along the north shore of Ontario’s Lake Superior, then it will head over Hudson Bay before gliding across the northern tip of Quebec, Baffin Island, and Greenland. The annular eclipse will even be visible at the North Pole before it races across the Arctic to Siberia.
Though few people will be able to witness the full ring of fire, millions across a larger stretch of the Northern Hemisphere will get to see a beautiful partial eclipse. While an annular eclipse is only visible in a narrow strip along the surface of our planet, where the moon aligns perfectly with the sun, observers in a much wider area can see part of the sun blocked by the moon.
Viewers across most of Europe will see a bite taken out of the sun during the middle of the afternoon. Viewed from northern Sweden and Norway, up to 50 percent of the sun will appear covered during the maximum part of the eclipse, while the United Kingdom will see anywhere from 18 to 38 percent of the sun covered up.
The southern limit of the eclipse in Europe will run just south of Spain, north of the city of Rome, Italy, and through Belgrade, Serbia, where only one percent of the sun will appear covered by the moon’s silhouette.
A crescent sunrise
In much of northeastern North America, the eclipse will already be in progress at sunrise. If the skies are clear, a spectacular crescent-shaped sun will appear above the horizon for people in major metropolitan areas, including Boston, New York, Philadelphia, and Washington, D.C.
Because the eclipse occurs around sunrise, it’s important to scout out a good viewing spot beforehand with easy views of the eastern horizon. The biggest challenge to catching the Devil’s Horns effect for city dwellers will be finding a spot that has a totally unobstructed view of the sunrise.
“The essential things are to be on time, make sure you have a good line of sight to the sun, and be serious about eye safety,” says Graham Jones, an astrophysicist who works with the website timeanddate.com. “For a sunrise eclipse, you need a position with a clear view to the horizon, like a hilltop or tall building.”
When the eclipsed sun rises, optical effects may make it appear redder and larger than it actually is. The sun’s distinct coloration at dawn and dusk is due to the fact that sunlight must pass through more of the atmosphere to reach our eyes than when we see it at high noon. When light has to travel longer distances through the gases in our atmosphere, much of the shorter, bluer wavelengths get absorbed and scattered, while longer, redder wavelengths reach our eyes.
Particles in Earth’s atmosphere can also affect the sun’s colors. How orange or red the sun will appear while near the horizon depends on how much dust or pollen is in the air at the time.
In addition, the rising sun may appear larger to our eyes than it actually is. Since there are objects closer to us in the foreground, our brains compare them to the rising sun, creating the illusion that it is larger near the horizon.
Seeing the eclipsed sun
Whether you are viewing a partial or annular eclipse, you’ll need to bring verified solar filter glasses to protect your eyes from injury. Solar filters are especially important if you're using cameras, binoculars, or telescopes, which magnify light from the sun.
Of course, to see the eclipse from the best locations and at the right time, the weather will have to cooperate—and it seems that will be tricky for some observers.
“For the big partial-eclipse sunrise in northeastern North America, a little bit of good fortune will be required. When we see the sun low on the horizon, we're looking through much more atmosphere than when it's overhead,” Jones says. “This produces spectacular sunrise colors but also means there's more chance of clouds blocking the view.”
If you are clouded out or can’t make it into the eclipse pathway, the Virtual Telescope Project and timeanddate.com will offer livestreams of the encounter beginning at 4:00 a.m. and 5:50 a.m. ET, respectively, on June 10.
And if you miss this event, additional opportunities to see a solar eclipse will occur in the coming years. On October 14, 2023, an annular eclipse will sweep across the continental United States, from Oregon down through Texas and into South America, with a partial eclipse visible across nearly all of both continents. Just six months later, on April 8, 2024, a total solar eclipse will cut a path across North America from Mexico up to Quebec, crossing several U.S. states along the way.
Andrew Fazekas, the Night Sky Guy, is the author of Star Trek: The Official Guide to Our Universe and the second edition of Backyard Guide to the Night Sky. Follow him on Twitter, Facebook, and YouTube.