UD astronomer explains solar eclipse
Animation by Paul Puglisi August 11, 2017
Q&A with Judi Provencal on “path of totality,” safety glasses and stargazing
From astronomers to citizen scientists, the science curious and those who couldn't name a single planet -- the Aug. 21 solar eclipse is an event that everyone in the U.S. (and North America, actually) will experience, though in much different degrees.
Millions will experience the phenomenon at 100 percent, many more millions in something far less (in the U.S. the least coverage will be about 49 percent). The upper reaches of Greenland drop to 1-3 percent.
If the skies allow, millions within a 70-mile swath of the nation will see a total eclipse that day -- as the moon passes between the earth and sun -- a spectacular and unforgettable experience that can be experienced nowhere else. The sky will grow dark, crickets will chirp and birds will head home to roost. The rest of North America, Central America, Mexico and the Caribbean will see a partial eclipse. (In Newark, Delaware, a partial eclipse is predicted to begin at about 1:20 p.m., reach its maximum -- just under 77 percent -- about 2:43 p.m. and be done by 4:01 p.m.)
UDaily spoke with Judi Provencal, associate professor of astronomy at the University of Delaware and resident astronomer at the Mt. Cuba Astronomical Observatory, Delaware's only public observatory, to talk about the eclipse and other astronomical wonders she knows about. Her research focuses on asteroseismology, which is the study of how stars move and what those movements may tell us about stars' internal structures. Her specialty is pulsating white dwarf stars.
Q: This eclipse is special and getting lots of attention - why?
A: The special thing about this eclipse is indeed that it is the first eclipse to cut across the U.S. in nearly 100 years. It will be visible to millions of people who wouldn't ever even think about seeing such a thing. It will probably be the most photographed/videoed eclipse ever. And maybe it will motivate the next generation of astronomers. A solar eclipse was one of the things that got me interested in astronomy.
Q: What is it like to see a total solar eclipse?
A: Solar eclipses are just spectacular to watch. This one is in the middle of the day and all of a sudden things will get dark, the brighter stars will be visible and you will see the corona of the sun. We live in a lucky time, when the moon's apparent diameter and the sun's apparent diameter are roughly the same. In about 500 million years, there won't be any eclipses. The moon is moving farther away from Earth all the time, so its apparent diameter is going to shrink. We live in a lucky time. This eclipse is going to be fantastic.
When people get all excited about lunar eclipses or about the "Super Moon," I might roll my eyes a little. Lunar eclipses are easily visible to everyone on Earth's night side and it is hard to really detect any difference in the moon's size during a "Super Moon." This particular solar eclipse is following a path that will allow millions of people to experience totality. That is "super cool."
Q: Will you be in the 70-mile-wide "path of totality?"
A: I think just about all of the astronomers from around here will be there. Some of my students hope to go. But I will be at Mt. Cuba Observatory.
Q: Will it be a lot different here, where a partial eclipse is visible?
A: It will be completely different, yes. If it's cloudy out, you might not even notice it. If you really want to see a solar eclipse, you have to go [to the path of totality]. Here, it might seem like a cloud has gone over the sun. If you look through a telescope, you'll see the moon taking a big bite out of the sun. You'll see that with the eclipse glasses, too.
Q: Are those lenses and special glasses really important?
A: Yes. Don't ever look directly at the eclipse of the sun without protective gear. I don't want anyone to burn their eyes out. It can ruin your eyes. Galileo ended up blind and he did a lot of looking at the sun. When I was young, I remember looking at an eclipse reflected in a mud puddle. You need a solar shield or lens to look at it through a telescope or binoculars or camera, too. That way a lot of the light gets kicked out before it enters your eyes. I remember when I brought my telescope to show-and-tell in elementary school. This particular telescope had a solar filter that attached to the eyepiece instead of the front of the telescope. I remember setting up the telescope to look at the sun and all of a sudden there was smoke coming out of it. The filter had gotten so hot that it cracked and melted a bit. A very bad design!
Q: Our understanding of eclipses and astronomy has come a long way, hasn't it?
A: Yes. People used to believe a solar eclipse meant the end of the world. It was definitely not thought to be a good thing. Our understanding of the entire universe has really changed in the last 50-60 years. It was only in the early 1900s that we began to realize that the Milky Way was not the center of the Universe and there were other galaxies out there.
Q: Are telescopes helpful in viewing an eclipse?
A: We will use a 4.5-inch refracting telescope built in 1887 to view the partial eclipse at Mt. Cuba. This telescope has a solar filter. If you are viewing the total eclipse, the best way might be to just sit in a nice comfortable lawn chair and watch. The total eclipse will only last for a few minutes, so you don't want to lose time fiddling with equipment!
Q: 1887? There's a collector's item!
A: It's a 4.5-inch refractor with a lens made by the famous Alvan Clark. Francis du Pont was the original owner. He donated it to the observatory in the 1970s. It has an electric tracking motor now, but it didn't used to. It had a gear assembly with weights that hung down. You'd crank the weights up and they'd fall down at the right rate to make the telescope move. Now we have electricity, so they took all that out and put this motor in.
Q: When you say 4.5-inch, you are referring to the aperture? Can we translate aperture to diameter here?
A: Yes, the lens or the mirror.
Q: Mt. Cuba has other telescopes, too, such as ...?
A: We also use a 24-inch, an 11-inch, a 10-inch and an 8-inch. Some are good to see planets, double stars. With the big one you can see galaxies. And we have some binoculars that are pretty nice, too.
Q: What would you expect to see if you viewed the eclipse with a telescope that you might not see just using special eclipse-viewing glasses?
A: Hopefully, you'd see sunspots. But right now the sun is at a minimal activity level. Sometimes there is a lot of activity with sunspots and flares. But unfortunately, we're at a minimal activity level right now.
Q: Could you use Mt. Cuba's big 24-inch telescope to look at the partial eclipse?
A: No way. You can see galaxies with it. But it was made to look at faint things, not to look at the sun.
Q: Are you planning to add to your telescope inventory?
A: We are working on a plan to install a new 1-meter-class telescope at Mt. Cuba Observatory. The cost will be around $2.3 million. The new telescope will be housed in a separate building designed to minimize thermal emissions. Heated air moving in front of the telescope makes stars look like little cotton balls instead of nice, sharp points of light.
Q: What are your students seeing when they start out?
A: Right now, there is a lot to see in the evening sky. Jupiter and its moons are visible to the west. Saturn and its rings are visible to the south. They are learning the brighter stars like Arcturus, Vega, Altair and Deneb. They also see satellites such as Hubble and the International Space Station when they pass by. We are using the 24-inch telescope to look at fainter objects like star clusters and galaxies.
Q: And things like your specialty - pulsating white dwarf stars? What are they?
A: White dwarfs are dead stars, remnants of the solar system. The sun will be a white dwarf in about 5 billion years.
Q: Do you have a super star? A favorite?
A: That would be a pulsating white dwarf called GD358. Not a very interesting name for a very interesting star! It pulsates every 10 minutes, so you can easily detect its brightness changes. Sometimes it changes its pulsation frequencies, so you are never sure what you will get!
Q: If you miss this eclipse, will there be another anytime soon?
A: In 2024, another total solar eclipse will come up the East Coast.
Q: What advice do you have for those who want to see this one?
A: If you have a chance to go to the path of 'totality,' you should go. You won't regret it. One of the coolest things I read was how Google is setting up amateurs all along the totality path to construct a movie of the entire eclipse as it crosses the continental U.S. They'll all need solar filters, but the movie should be neat!
Q: Any other suggestions for those interested in astronomy?
A: Sometimes the best thing to do is just look up. Go outside on a clear night with a blanket, lie down on the grass and look up. No special equipment requirements. You can see meteor showers, comets - on any night that it's dark and clear. Check out public nights at Mt. Cuba Observatory and go to other public events. A few years ago, myself and two other professors from UD went to a park in Elkton (Maryland) with a small telescope to watch the Venus transit. People joined in as they were walking by.
For more information on safety issues related to watching the eclipse and eclipse events, click here.