Podcaster: Jay Pasachoff

Title: The Minus-first anniversary of the Great American Eclipse

Organization: Williams College and Caltech

Links: and

Description: Count down to Total Solar Eclipse 2017

Bio: Jay Pasachoff, Chair of the International Astronomical Union’s Working Group on Eclipses, is Field Memorial Professor of Astronomy at Williams College and a Visitor at Caltech. He has viewed 64 solar eclipses, and is an expert on both their use for scientific observations and their use for public education. Pasachoff is a former president of the International Astronomical Union’s Commission on Education and Development and Chair of the Historical Astronomy Division of the American Astronomical Society. He received the Education Prize of the American Astronomical Society, the Janssen Prize of the Société Astronomique de France, and this year’s Richtmyer Memorial Lecture Award from the American Association of Physics Teachers. Pasachoff is the author or co-author of The Cosmos: Astronomy in the New Millennium, the Peterson Field Guide to the Stars and Planets, and Nearest Star: The Surprising Science of Our Sun plus, on a more technical level, The Solar Corona, as well as a new, 2017 book, The Sun, for the Science Museum, London.

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Today is the minus-first anniversary of the Great American Eclipse of August 21st, 2017.  One day [should be One year] from today, the shadow of the Moon will sweep across the continental United States from upper left to lower right, from Oregon to South Carolina.  And anybody in the narrow path that is only about 60 miles wide will be able to see totality.

Totality is very exciting.  As the Moon covers the Sun for the preceding hour and a half, it gets a little darker, but only in the last minute-and-a-half does it get dramatically darker, and then as the Moon entirely covers the Sun, Baily’s Beads become visible as the last little bits of everyday sunlight shine through the valleys that are aligned on the edge of the Moon.  The last Baily’s Bead glows so brightly compared with everything else that it is called the “diamond ring.”  We talk about the “diamond-ring effect.”  And then we will have totality, where we see the color corona, the outer atmosphere of the Sun.  It will be visible from about two minutes in Oregon to two minutes and forty seconds in the peak near southern Illinois and Kentucky, and millions or hundreds of millions of people should go into the path to see this total solar eclipse.

On the day of the eclipse, the shadow will come across the Pacific, and then will hit Oregon.  And once you get off the coast, where there’s haze, there should be good viewing.  And then Idaho.  And then it will go across Wyoming, where some people are going to Jackson Hole.  It will go through North Platte, Nebraska, hit northeastern Kansas, and go across Iowa, just going south of St. Louis (so people from St. Louis don’t have to drive very far).  It will go through Tennessee, clip the lower left corner of North Carolina, and go through South Carolina, exiting at Charleston.

But the path of totality is not the only thing you have to take into account.  You also have to take into account the chance of seeing the eclipse.  On the whole, it is much cloudier in the western [should be eastern] United States on August 21 in the afternoon than it is in the northwestern United States in the morning.  In fact, there is a meteorologist, Jay Anderson from Canada, who has substantial expertise in doing reduction of satellite views of cloudiness, and he has a map on his website at, and you can see color-coded maps of the chance of seeing the eclipse statistically.  Of course, statistics are not the actual thing on the day, but on the whole, it is much clearer in the western part of the track of this eclipse than it is in the southeastern part of the track.  So most of the very dedicated people will head to the northwestern United States.  But this eclipse will go near where a lot of people live, and people will be tempted to stay home to try to see an eclipse near home.

There is a lot of research that gets done at eclipses.  We only get a view of the outer layer of the Sun from the Earth for two minutes or so–that’s two minutes in Salem, Oregon, for example, where I will be; two minutes and forty seconds at the peak of the eclipse across the United States in Illinois and Kentucky, and if you only get a glimpse of something for a couple of minutes every year or two, you can imagine you want to go back for more.

We study the outer layer of the Sun and how it is heated to millions of degrees.  We study how the magnetic field holds it in place, a process that people on Earth are trying to harness to get fusion for clean energy on the Earth.  (The Sun does it very well, but 93 million miles away from us.)

We have spectra–the rainbow breaking down the light from the Sun that shows that iron atoms have been heated so hot that only million-degree temperatures will accomplish this.

We try to compare views from different places across the path in order to see motions.  For the Great American Eclipse of 2017 (and, incidentally, there is a wonderful website by Michael Zeiler at, you will be able to participate by taking pictures with whatever cameras you have, whether it’s a digital camera (Canon or Sony or Nikon) or even just an iPhone or other kind of smartphone.  And there is a project called Megamovie that I’m involved in that will try to put these pictures together to make a movie of the 90 minutes of changes in the corona as it crosses the United States.  There is also a Citizen project with 61 identical telescopes that are being put together to be spaced across the United States to get higher-resolution images of the Sun and that will also make a continuous movie and provide information for a lot of measurements as things go across the United States.

For the International Astronomical Union’s Working Group on Eclipses, I have a website at an easy-to-remember address:  So all you have to do on the web is go to and you’ll find lots of links to maps and weather statistics and information about how to observe the eclipse safely.   We really encourage everybody to see the eclipse because it is beautiful but whenever it is not totality, you do need a special filter to look at the Sun because the Sun is too bright to stare at, or you can project the image onto the ground, or just look under a tree, because the interstices of the leaves make little pinhole openings that project crescents on the ground when the Sun is only a crescent.

But the crescent parts, the partial parts, are really preparatory to the main event, which is the total eclipse of the Sun, and we certainly encourage everybody to try to get into the path of totality, the 60-mile-wide path that goes from Oregon to South Carolina on August 21, 2017.

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