Eclipse: Total or Partial - Which One's For You?

Aug 17, 2017

Bill Arden, in his observatory with his telescope, in the yard of his home in Milroy, PA.
Credit photo: Kristine Allen, WPSU

The Great American Eclipse is almost here.  On Monday, a ribbon of land about 70 miles wide, from the West coast of Oregon to the East Coast of South Carolina, will see a total eclipse of the sun. It will be the first total solar eclipse in the continental US since 1979.  We asked two astronomers about their plans, and what’s in store.  One will travel to the path of totality to see the total eclipse, and one will stay in Pennsylvania to watch the partial eclipse.

Retired astronomer Bill Arden has masters degrees in physics and astronomy, and spent 5 years doing research on the sun. He keeps his telescope out in the yard of his home in Milroy, about 40 minutes from State College.  It’s housed on a tripod in its own observatory, complete with a domed roof that slides open.

Let me open it,” Arden says, as he slides half the dome around to reveal the telescope.

The observatory is just a bit larger than a kid’s playhouse.  

“That’s my man cave,” Arden says with a smile. “It’s about 8 feet across. It holds the telescope nicely.”

He says the observatory is made from PVC – most of it recycled plastic. A solar panel outside on the deck provides the power to adjust the telescope.  Under the three legs of the tripod is a block of concrete that completely isolates the tripod and the telescope from the deck around it.

“So you can dance on the deck,” he says, “and the telescope never feels it.”

You have to have quite a fascination with the stars to have this kind of setup in your yard.  So I wasn’t surprised to hear that Arden’s planning to travel to see Monday’s total eclipse of the sun.

“As soon as I found out it was happening I said OK this is my first one, I’ve got to go do it.”

Since Pennsylvania will only experience a partial eclipse, Arden will head to Nebraska to visit family and watch the total eclipse. Although he’s never seen a total solar eclipse before, he knows enough to be certain the trip is worth it.

“You really won’t see much of anything until totality hits,” he explains. “So if you look at the sun through a pair of good solar glasses or a good solar filter, you’ll se the moon’s shadow take a bite out of the sun that will get progressively larger.”

But Arden says at that stage of the eclipse, while it’s still only partial, you won’t notice a change in the light yet.

“In other words, the sun could be 80 or 90% blocked and you won’t notice any difference,” he says.  “But in the seconds before totality, actually if you’re in a big open clear space, you’ll actually see the shadow of the moon coming toward you.  It’ll be like a fast-moving thunderstorm.”

The, suddenly, it will get dark.

“Dark enough that birds stop singing, the cicadas start to chirp, nighttime things start happening.”

But that nightfall, Arden says, is very short-lived.

“That lasts for, depending on where you are, 2 minutes and 40 seconds or something like that.  And then it goes back to being normal daylight again. So we’re all going halfway across the country for 2 and a half minutes (laughter).”

Chances are most of the eclipse photos you’ve seen show the corona of the sun encircling the dark disc of the moon. But, Arden says, that may not be how the corona will look during this total eclipse.

“We’re almost at solar minimum,” he explains.  “The sunspot cycle is about 11 years long and we go from very few sunspots to a peak of lots of sunspots, typically hundreds at a time, during solar maximum.”

And a lack of sunspots, Arden says, means the corona may look very different.

“If you looked at the corona during solar maximum, you’d see arcs and loops and streamers and things pointing out  all sorts of directions from the sun,” he says. “The field settles down a lot at solar minimum. And so at solar minimum if you look at the corona, it’s very likely that what you’ll see is just two long tapered streamers, one coming out of each side of the sun, around the solar equator.”

What Arden describes is what you’ll see if you’re travelling south or west from Pennsylvania to the path of total eclipse on Monday.  But if you stay and watch the partial eclipse? 

“If you’ve got a decent pair of solar glasses, you can look directly at the sun,” he says.  “And what you will see is the moon’s silhouette taking a bite out of the sun. And you’ll see it cover about three quarters of the sun, at the point where totality is South of you, and then start to move off again. You won’t see the darkness of totality.  But you can definitely see the bite out of the sun.”

Meanwhile, at Penn State University, astronomer Chris Palma has never seen a total solar eclipse, either.  But he’s passing it up to stay in Pennsylvania.

“Millions of people are planning to travel to somewhere along that path to see the eclipse,” Palma warns. “There’s a lot of worry that traffic is going to be pretty serious on that day.”

Palma says he thought about travelling with some of his colleagues to see the total eclipse. But decided to stay and watch the partial eclipse in Pennsylvania.  

“The more I thought about it,” he says, ”there’s going to be thousands of students here at Penn State who are going to want to see the partial solar eclipse.  While it’s not quite as spectacular as a total solar eclipse, it’s still not something that you get to see that often. So I’m organizing a group of us to be on campus and in the community handing out eclipse glasses so that people can safely observe the eclipse while it happens.

Safety, Plama says, is crucial.

“Safety should be on all of our minds,” he says. “ You know, some people are just thinking, ‘Oh, I’ll just put on some heavy sunglasses I have.’ Those will not be safe, either.  Please do go outside.  Just don’t look directly at the sun without solar glasses that you know are safe.”

If you can’t get outside to view the eclipse, or you don’t have special eclipse glasses, you can, of course, watch the live stream online, courtesy of NASA.

“They have a great website,” Palma says, “that’s very easy to find, that brings together all of their 2017 eclipse information in one place.  And that’s where they’ll be live streaming it. And so that’s where I would go, is NASA’s main eclipse website.”

If you miss this eclipse altogether, take heart. On April 8th, 2024, there will be another total solar eclipse.  The path of totality for that eclipse will cross the Northwest corner of Pennsylvania, stretching from from Titusville to Erie.

Check out this map of official NASA eclipe events.

Good eclipse resources from NOAA can be found here.

To see what towns are in the path of totality, click on this interactive Google eclipse map.