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July 16th: The July 22nd Total Solar Eclipse


Date: July 16, 2009

Title: The July 22nd Total Solar Eclipse


Podcaster: Jay Pasachoff

Organization: Williams College, Working Group on Eclipses of the International Astronomical

Description: The longest total eclipse of the 18-year interval of eclipses will occur on July 22. It will be mainly visible from China and India, and from some ships in the Pacific. Tens of millions of people will see it. Jay Pasachoff will head a research group of faculty and students from Williams College to study the sun from the ground at the eclipse simultaneously with satellites making observations from space, in order to get a complete picture of the solar corona at that time.

Bio: Jay Pasachoff, Chair of the International Astronomical Union’s Working Group on Eclipses, is Field Memorial Professor of Astronomy at Williams College and is on sabbatical at Caltech. He has viewed 48 solar eclipses, and is an expert on both their use for scientific observations and their use for public education. Pasachoff is past president of the International Astronomical Union’s Commission on Education and Development. He received the Education Prize of the American Astronomical Society. Pasachoff is the author of textbooks on astronomy and of the Field Guide to the Stars and Planets.

Today’s sponsor: This episode of ’365 Days of Astronomy” is sponsored by the American Astronomical Society, the major organization for professional astronomers in North America, whose members remind everyone that One Sky Connects Us All. Find out more or join the AAS at aas.org.


I’m Jay Pasachoff. I’m the Field Memorial Professor of Astronomy at Williams College in Williamstown, Massachusetts, and I am the chair of the International Astronomical Union’s working group on solar eclipses.

The most beautiful and remarkable thing that anybody can see in the natural world, I think, is a total eclipse of the Sun. For it to get very dark in the middle of the daytime, for the Sun to go away at midday or sometime in the morning or afternoon, can even be frightening for many people. But, fortunately, we know and we can predict very well when we have these total eclipses of the Sun.

If you stay at home, you probably have to wait about three hundred years for a total eclipse to envelop you. But, if you can travel, and travel is a lot easier these days than it used to be hundreds of years ago, you can see an eclipse in the world about every year and a half. That’s a total eclipse when the moon completely blocks the sunlight; it keeps the sunlight from hitting the sky, turning the sky blue, and you can see the faint outer parts of the Sun that are normally hidden behind the blue sky.

The outer part that we’re most interested in usually is the solar corona, this white crown of light that we see only for a few seconds or minutes during a total eclipse of the Sun. There’s a series of these total eclipses: some longer, some shorter; some may last only a second or two and some go up to almost, these days, seven minutes long. The longest in the eighteen year eleven and a third day series is happening this summer on the 22nd of July. You have to go to India or China to see it as a total eclipse or some of the Japanese islands out in the Pacific, and many dozens of eclipse astronomers and many thousands of eclipse tourists will go to see it. More and more people just come to see eclipses as tourists because if you see one you want to go back and see the next one, and bring a few friends or relations also. So the eclipse tourism has been growing at quite a pace.

My scientific studies involve the solar corona, in particular. The everyday surface of the Sun is 6000 degrees and the corona is a couple of million degrees hot, so a major scientific question is: how does the corona get to be so much hotter than the underlying layers. How does that solar corona get to be millions of degrees? It was noticed some decades ago from x-ray astronomy of the Sun that the corona is hottest over the sunspot regions, over the active regions on the surface of the Sun, so we are sure that the heating of the corona has to do with the Sun’s magnetic field. But there are a dozen or so different solutions to the question of how the solar corona is heated and that means that nobody really knows the answer. There are a few different alternatives including, for example, mainly waves coming up on the loops in the corona that are held in place by the magnetic field, and so some whipping back and forth of these loops could provide some energy to heat the corona.

We are looking for, in my experiments, oscillations with very short periods, several times a second. [We are taking] a series of photographs through filters that show a very pure color of light that’s emitted by the corona and we’re looking for signs of these waves. In particular, the corona gives off light that comes from Iron that has lost half of its twenty-six normal electrons and it has to be pretty hot to take electrons off an iron atom one at a time. The overall corona, the main white part, actually comes from sunlight, normal sunlight, scattering off the electrons in the corona itself and not just from those odd atoms of iron.

In any case, I’ll be going with a few students from Williams College, where I am a professor, and some colleagues from Williams College and elsewhere, to China: to the mountains outside Hangzhou, not far from Shanghai. There will be ten million or more people in Shanghai who can see the eclipse, but you wouldn’t want to try to observe from the middle of a city. We’ll get to a pure place up in the mountains outside Hangzhou and we’ll hope for clear weather on that day.

Now, there are other possibilities for seeing eclipses, too. Sometimes, the moon doesn’t entirely cover the sun. It’s just a little further away than average as the moon goes around the Earth and a ring of everyday sunlight remains. The word for ring is annulus, so they are called annular eclipses, and there is one of those about every eighteen months, too.

In fact, in 2012, on May 20th, there will be an annular eclipse that will start in Asia and come across the Pacific, and reach the United States, the west coast at the northern part of California and come down as far as Lubbock, Texas. So people in that band, a couple of hundred miles wide, will be able to see an annular eclipse, and people to the north and south of that will see a partial eclipse. Depending on how far you are from that path, there will be a greater or lesser percentage of the sun that is covered.

The next total eclipse of the sun that crosses the United States won’t be until August 21st, 2017. And on that occasion, the eclipse will cross from the Pacific Northwest all the way over to Georgia, with partial phases covering essentially the whole United States. So, many people are looking forward to that one and 2017 isn’t as far in the future as it used to be.

The eclipses are worth waiting for and worth watching; even just to see a partial eclipse is interesting. It is a real sign that we can predict what the universe is like. We can get the times of these eclipses down to a fraction of a second. The idea that students look at and can study these eclipses is inspiring for their continuing their studies, their studying harder, their getting excited in the natural world.

Whenever the sun is not completely totally eclipsed, then whatever is left is too bright to look at safely, and you have to take precautions such as looking through a special filter. These are made out of a plastic mylar quite often and can be gotten for a few pennies apiece, often sold for a dollar. You can also just make a pinhole camera, punching a hole in a piece of paper or cardboard, and letting the eclipse project on a wall or on a second piece of paper.

So there are easy and safe ways of looking at the partial eclipses, but the exciting part is really to be in the zone of totality itself, and let the sky go dark around you. The partial eclipse before and after take an hour or an hour and a half, but then you get the few second or minutes of totality and it’s well worth the trip. I sure hope the skies are clear in China on the 22nd of July and that we get a good view of this year’s total eclipse of the sun.

End of podcast:

365 Days of Astronomy
The 365 Days of Astronomy Podcast is produced by the New Media Working Group of the International Year of Astronomy 2009. Audio post-production by Preston Gibson. Bandwidth donated by libsyn.com and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. Until tomorrow…goodbye.

4 Responses to “July 16th: The July 22nd Total Solar Eclipse”

  1. Good luck to all eclipse chasers in China

  2. Chris F says:

    Thank you for your work!

  3. John says:

    Sweet report; many thanks.


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