Want To Tell Time By The Eclipse? These Vermonters Have You Covered

Aug 11, 2017

On August 21, the entire North American continent will witness a full or partial eclipse of the sun. And a couple of Vermonters have come up with an activity that anyone can do to tell time as they follow the eclipse’s progress.

According to NASA, the path of totality – where the moon will completely cover the sun, stretches from Salem, Oregon to Charlestown, South Carolina. But Bill Gottesman has invented a solar eclipse sundial that will work best in places like Vermont, where the eclipse is partial.

"This idea of using the rotation of the sun’s crescent during an eclipse came to me in 2012," says Gottesman. "There was an eclipse out in California and it just occurred to me that I could use the sun’s eclipse to tell time. What’s fun about it is the sundial works for about two hours and then you throw it away. Then it’s no good to you anymore."

Gottesman is a retired physician from Burlington and a self-described sundial enthusiast. He wants to share his eclipse sundial with as many people as possible. That’s where his old friend Dan Axtell comes in. Axtell is a freelance web designer and computer programmer who lives in Westminster.

"He’s been a superb computer programmer since high school, when you had little punch tapes to read your programs in with," Gottesman says of his friend. "I am not a programmer and I needed help to bring my idea to a web page where anyone could print out a sundial for their location in the country. I went straight to Dan because I thought it would be a fun project, because he’s also math-y like me."

Gottesman demonstrates how to project an image of the sun onto the printed sundial. He warns never to look directly at the sun without proper eye protection.
Credit Amy Kolb Noyes / VPR

EclipseSundial.com is free for anyone to use. You just need to put in your location, and the website will produce a custom sundial for you. The sundial itself looks like a series of rotating lines.

Once you print out your sundial, you place it on the ground facing north and project the eclipse image onto the paper using a pinhole in a card or low powered binoculars.

Gottesman projects two images of the sun onto his eclipse sundial. The larger circle is projected through binoculars. The smaller image is from a pinhole in an index card.
Credit Amy Kolb Noyes / VPR

Detailed instructions are given on the site. It’s important to remember never to look directly at a solar eclipse.

As the moon covers the sun, the projected image becomes a crescent. The sundial uses the rotating position of that crescent to tell the time, as Gottesman explains.

"So it starts here as a faint oval on the paper," he says, "and as a bite gets taken out of it you will just follow it along and see which sundial line it matches with."

In Vermont, the August 21 eclipse will start a little before 1:40 in the afternoon and last just over two hours. Gottesman says it will peak at 2:40, at which time the sun will be 68 percent covered around Burlington. Axtell adds it will be 71 percent covered in southern Vermont, which is closer to the path of totality.

Axtell also notes Vermont will be front and center for this country’s next total eclipse.

Sundials can come in many shapes and sizes. Here, Gottesman shows how to use the human sundial he designed inside the Burlington Earth Clock.
Credit Amy Kolb Noyes / VPR

"In 2024 there’s going to be an eclipse here that’s going to pass right over Burlington," he says. "The totality area is about 70 miles wide, so the entire north border of Vermont is part of the totality of the eclipse. Canada gets to share in a lot of that too."

That will be the afternoon of April 8, 2024. Having learned a thing or two about eclipses and eclipse enthusiasts, Axtell has some advice for northern Vermont inn and hotel owners.

"You need to raise your rates now," he advises. "People in Oregon got caught off guard on that one."

Gottesman also built this helical sundial at ECHO, in Burlington.
Credit Kathleen Masterson / VPR

Axtell says a total eclipse of the sun only happens about every 360 years for any given place on the planet, although there was one relatively close to here 47 years ago.

"Well, the closest we’ve had to a total eclipse around here was back on March 7, 1970, where Nova Scotia had a total eclipse of the sun, which Carly Simon made famous," he says referencing the song You're So Vain.