Total eclipse of the Sun. The moon covers the sun in a solar eclipse.

Credit: Pitris / Getty Images


There goes the sun. Again?

Just seven years after the last total solar eclipse in the United States, millions of Americans will once again be in the path of daytime darkness April 8

Roberto Molar Candanosa
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If you have one of those household drawers where random stuff collects, you might want to rummage through it looking for an old pair of eclipse viewing glasses. It was just back in August 2017 when we needed special light-blocking eyewear to view a total solar eclipse that cut a swath across the country. Dubbed "The Great American Eclipse," its "zone of totality"—the shadowed region where the sun is completely blocked by the moon—stretched in a narrow band from Oregon to South Carolina. (Outside this band, Baltimore experienced a partial eclipse that year with 80% of the sun blocked by the moon.)

On April 8, the moon and the sun will again do their sky-darkening celestial dance. This time, the band of totality stretches from Mazatlan on Mexico's west coast and moves northeast through Texas as part of a sweeping cross-country arc ending in Newfoundland, Canada. Major cities in its path include San Antonio, Dallas, Little Rock, Indianapolis, Cleveland, and Buffalo. With deference to Bonnie Tyler's chart-topping hit, maybe this one could be dubbed "Total Eclipse of the Heartland." In Baltimore, the optimal viewing time is expected to be 3:21 p.m. EDT, with the partial phases extending from about 2 to 4:30 p.m. or so.

We checked in with William Blair, an astrophysicist and research professor in the Department of Physics and Astronomy at Johns Hopkins University, for his thoughts on what we can expect.

Partial solar eclipse as seen from Wyman Park Building, June 2021

Image caption: June 2021 partial solar eclipse viewed from the Wyman Park Building

Image credit: Will Kirk / Johns Hopkins University

Is there anything special about this latest total solar eclipse?

Well, for one thing there won't be another total solar eclipse visible in the U.S. until 2044. But this eclipse will be different from the one in 2017. The moon's orbit is slightly elliptical. So the angular size of the moon is a little smaller when it's farther away, and a little bigger when it's closer. This year the moon is closer to us than in 2017. The length of the time that you were in shadow in 2017, if you were right on the totality center line, was a little over two minutes. And this time it will be over four minutes long—all because the moon is closer. And the path of totality will be wider as well.

What should we consider if we want to travel to experience totality?

Clouds! [laughter] The difficulty with this one is that the Northeast in April is not known for being spectacularly clear. So it'll get dark in the totality zone, but whether you can actually see the eclipse or not is just going to depend on the weather. I think a lot of people are heading down south to Texas and Mexico hoping that the weather is a little clearer down that way.

What can we expect here in Baltimore?

It will be another partial eclipse here with some 90% of the sun covered. If you have the special glasses and look at it, you will see the bright disk of the sun with a substantial chunk taken out of it that will change over time. It'll get to a certain point, maximize, and uncover again. You might see the character of the light change a little bit if it's clear here. It's an odd light. The light levels go down, and if the sun's out, it is still producing crisp shadows. This is in contrast to evening twilight when things kind of soften in terms of the shadows.

Is it worth getting closer to the totality but not all the way in it?

Not really. The amazing thing about an eclipse is that you could be where the sun is 99% covered and it's not the same as being 100%, when the solar disk is completely covered and you see the corona around the outside. In a 99% eclipse, you still have a piece of the sun that's uncovered and its light completely dominates so you don't see the corona. So people who say, "Oh, I'm close to totality—I'm going to stay here" will not experience totality or see the corona.

Tell us more about the corona.

It's basically the tenuous outer layers of the solar atmosphere. When you see the bright sun, that's called the photosphere. You can see sunspots and things there. That's the so-called surface of the sun. (Well, the sun doesn't have a hard surface like the Earth, but basically, there's a photosphere where the light escapes and that's what we see.) There is a tenuous region of the extended solar atmosphere called the corona, where magnetic fields and high-energy particles come out of the sun and ionize the tenuous gas around the sun. That's the halo around the sun you can see when the bright disk is completely covered during totality. During totality, you can look at it without glasses and take pictures of it.

It's pretty amazing, right?

Absolutely spectacular. And not just the eclipse itself, but then just seeing the surroundings get dark in the middle of the day. Sometimes animals and insects and birds and whatnot start to do funny things because they don't understand what's going on. We experienced totality in the Tetons in 2017. You could see the shadow coming and then it sweeps over you and all of a sudden, you're in the dark. The only other time I experienced it was as a college student in 1972. We were driving across Canada listening on transistor radios to figure out what the weather was going to be like and where we should try to go. It sounded like Nova Scotia had the best chance of being clear, so we kept going east until we got to Nova Scotia, and that's where we watched it.

Wait, you went up to Nova Scotia to see the total eclipse of the sun? Did Carly Simon write her chart-topping hit "You're So Vain" about you?

Sadly, no. I went in a college van, not a Learjet!