Podcaster: Jay Pasachoff
Title: The 2017 annular eclipse and a post-Pluto spacecraft mission
Organization: Williams College and Caltech
Links: http://www.eclipses.info and http://www.totalsolareclipse.org
Description: Preparation for the annular solar eclipse in Patagonia, the southern part of Argentina and Chile, on February 26.
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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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Transcript:
Today boasts an eclipse of the Sun, but you have to go to the southern part of South America to see the Moon go entirely in front of the Sun. The Moon is a little smaller than average today, so it doesn’t completely block the Sun, leaving a ring–an “annulus”–of everyday sunlight. Such an annular eclipse occurs somewhere in the world about every 18 months.
The last annular eclipse passed over southern Africa and into the Indian Ocean on September 1, 2016, and my wife and I went to the Indian Ocean island Réunion, a part of France. It was an 11 hour nonstop flight from Paris. We were joined there by several other eclipse aficionados. The weather was clear, and we had a great view of the Moon gradually covering more and more of the Sun for over an hour until it slid completely inside the solar disk for a couple of minutes. Because part of the everyday Sun remained visible at all times–the solar photosphere (the sphere from which the light, “photos” in ancient Greek–comes) we had to leave our solar filter on at all times.
Today’s annular eclipse begins in the Pacific Ocean and then crosses southern Chile and Argentina. For the last few days, colleagues from Argentina ran an eclipse symposium in the picturesque city of Esquel. Today we are driving about four hours south to reach the centerline of the annular eclipse. The path of annularity is only about 55 kilometers wide, and about 99% of the Sun’s diameter will be covered. Annularity will last about a minute, and it will be good practice for us to photograph the event under such a strict deadline, given that we are getting ready for this summer’s coming total solar eclipse in the United States.
The end of today’s annular eclipse will cross Angola and wind up clipping a bit of Zambia and of the Democratic Republic of Congo.
Interestingly, the path of today’s eclipse is similar to the path that the occultation of a faint star by an unusual object in the extreme outer solar system will take on July 17. NASA’s New Horizons mission, run by the Southwest Research Institute in Boulder, Colorado, and the Johns Hopkins University Applied Physics Laboratory, passed Pluto and Charon on July 14, 2015. Scientists had hoped that in the 10 years or so that the spacecraft was en route to Pluto, a so-called Kuiper belt object would be found in the direction that the spacecraft was traveling so that New Horizons could photographic up close. Finally, the scientists involved had to use a lot of Hubble Space Telescope time to find some objects in that direction, and they settled on pointing the spacecraft toward 2014 MU69.
But MU69 may be only 35 km, 20 miles, or so across, and its position is not known accurately enough to target the spacecraft to fly very close. If we succeed in observing it passing in front of a star–with the starlight winking out for a couple of seconds–on June 3, then NASA can target its instrumented airplane with a 2.5-m, 100-inch, telescope for the July 10 or July 17 event. And we can try to get a lot of ground-based telescopes starting with the June 3 event to make a “picket-fence” every 25 km, 15 miles, or so on a north-south line to try to pinpoint just where MU69 is. If we succeed, then NASA can retarget the spacecraft a bit, and we’ll get closer and better images on January 1, 2018, when New Horizons reaches there.
But back to solar eclipses. Our photography at today’s annular eclipse is largely in preparation for the Great American Eclipse of August 21 this year. The 120-km, 70-mile-wide path of totality will sweep across the Continental United States from Oregon to South Carolina, with historical cloudiness statistics favoring the northwest portion. Partial phases will be seen from the northern part of South America up through Central America, Mexico, the whole United States (including Hawaii and Alaska), and almost all of Canada. Near sunset, the partial phases can even be seen from west Africa and from westernmost Europe. Maps are linked to my website for the International Astronomical Union at http://eclipses.info. Only within totality do you see the most exciting eclipse phenomena: Baily’s beads, the diamond rings, and totality. And only during totality and the last bit of diamond ring can you safely stare at the Sun without a filter–indeed you have to take your filter off then or you won’t see anything, since the corona is about a million times fainter than the everyday Sun. Do try to arrange to be in the path of totality on August 21!
365 Days of Astronomy
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