Date: January 10, 2010
Podcaster: Jay Pasachoff
Organization: Williams College: http://www.williams.edu/astronomy
Working Group on Eclipses of the International Astronomical Union: http://www.eclipses.info
Description: In 2010, there will be two central eclipses of the sun: an annular eclipse on January 15 and a total eclipse on July 11. This podcast discusses the annular eclipse, which will be visible in a path from Africa, including Kenya, across the Indian Ocean, over the Maldive Islands, across the southern tip of India and the northern end of Sri Lanka, and then across parts of Bangladesh and Myanmar. The band of annularity winds up crossing China. A partial solar eclipse will be visible for hundreds of miles to either side of the band of annularity. At the center of the band of annularity, the 92% coverage of the sun’s diameter lasts over 10 minutes. Safe solar observing procedures, including a solar filter for direct view or projection methods for indirect view, must be used throughout the annular eclipse, even during annularity, since part of the solar photosphere remains visible.
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.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Craig Clark.
This is Jay Pasachoff, I’m the Field Memorial Professor of Astronomy at Williams College in Williamstown, Massachusetts, and the chair of the Working Group on Solar Eclipses of the International Astronomical Union.
There will be two eclipses of the sun in the year 2010. The first is an annular eclipse of the sun that will occur on the 15th of January. An annular eclipse is when the moon is a little further than average away from the earth, in its elliptical orbit around the earth, and its angular size in the sky is therefore slightly smaller than the angular size of the sun. So the moon can be silhouetted against the sun but doesn’t cover the sun entirely, and we see a ring, or annulus, of everyday sunlight around the black disk of the moon. This is known as an annular eclipse. It never gets completely dark outside during an annular eclipse, at least not the 92 percent coverage that we will have at this annular eclipse. Sometimes they’re close to one hundred percent. Because it doesn’t get completely dark, we won’t be able to see the solar corona, the diamond ring, or the fantastically interesting and beautiful phenomena that one sees at a total solar eclipse, but still annular eclipses are interesting to see. You have to keep a solar filter on to look through for the whole time. The partial phases that last an hour and a half and the annular phase, which, for this eclipse, lasts, in many places, over ten minutes – very long for an eclipse. The longest total solar eclipse possible is only in the seven minutes, and the ones that are occurring these days are never as long as seven minutes, whereas I will have over ten minutes of annular eclipse at the southern tip of India on the 15th of January, 2010.
One doesn’t do a lot of science at annular eclipses usually because you can’t see the corona, but there are some things you can do scientifically, including radio observations. In India they have a wonderful radio telescope known as the Giant Metre-wave Radio Telescope. It’s near Pune, which is east of Mumbai, and we’re arranging to use it in collaboration with some Indian scientists to observe the sun. In particular, if there are active regions on the sun (and this is by no means certain because we’re at a very low minimum in the sun spot cycle), as the moon covers the active region on the surface of the sun, its radio emission diminishes and we can tell very precisely where on the sun these regions are and how big they are. You get two cuts across each region on the sun, one when it’s covered and one when it’s uncovered, and the two together give you the position very precisely. So we’re hoping for an active region on the 15th of January so we can do those radio observations.
I’ll be at the very southern tip of India, the cape there, south of Trivandrum. There will be millions of people around; it’s a very heavily populated part of India. And it will be very interesting to watch the phenomena, the moon gradually cover the sun over an hour and a half or so, and then the ten minutes on annularity, and then the uncovering at the end. The path of annularity begins in the middle of Africa, comes over Nairobi and Kenya and goes over the Indian Ocean. It then passes the Maldive Islands, which we’ve heard a lot about recently because they’re so low-lying that they’ll be some of the first casualties of the continued rising of the oceans from global warming. Then the eclipse hits the southern tip of India and the northern part of Sri Lanka and goes back over the ocean. It will hit a very southern protuberance of Bangladesh and go through Myanmar and into China. That’s the path of annularity, a hundred or so kilometers wide, but then for a thousand or so kilometers to either side of that there’ll be a partial eclipse, so may tens of millions of people will be in a zone where they will be able to see a partial eclipse. It will be fun to watch but not as dramatic as a total solar eclipse.
The total solar eclipse that will occur in 2010 will be on July 11th, and that won’t be seen by very many people at all. It is largely over the Pacific Ocean, where it will cross some normally uninhabited atolls not far from Tahiti, so there’ll be some ships there and some few expeditions out of Tahiti to see that. The major land in the way is a very unusual island, Easter Island. It’s in the middle of the Pacific, some 4000 miles west of the coast of Chile, and it is part of Chile. At sunset the eclipse reaches the Patagonia region of Chile very low in the sky with very poor weather forecasts at that time in Chilean winter, so there isn’t a good possibility of seeing it from the ground there, though perhaps there’ll be some air flights. Certainly it’s a wonderful opportunity to see a total solar eclipse, especially if you can get to a site like Easter Island or out in one of the ships or in the air over Chile or anywhere else.
The two central solar eclipses, the annular eclipse of January 15th and the total eclipse of July 11th, 2010, will be succeeded by a year, 2011, when there are no central eclipses at all. There will be four partial eclipses in 2011 visible at various parts of the globe.
This is Jay Pasachoff, professor of astronomy at Williams College in Williamstown, Massachusetts, and chair of the International Astronomical Union’s Working Group on Eclipses. We spend a lot of time and effort from the Working Group on Eclipses of the International Astronomical Union in educating the people in the various countries on how to watch the eclipse safely, what kind of eye protection they need for all times except when there is a total solar eclipse. The partial phases or an annular eclipse require eye protection or looking away from the eclipse in a projected image, either from a telescope or binoculars, or from even a simple pinhole camera, a hole punched in a piece of paper, projecting an image of the shape of the remainder of the sun onto a cardboard or onto a wall or even just under a tree from the interstices of the leaves onto the ground. So it will be interesting for all kinds of people to see these eclipses – partial, annular, and total.
End of podcast:
365 Days of Astronomy
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