Date: June 29, 2012

SolarEclipseTitle: Transit of Venus 2012 Observations

Podcaster: Jay Pasachoff

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

Description: Noted astronomer Dr. Jay Pasachoff talks about the 2012 transit of Venus, about which he spearheaded observations from the ground and from space.

Bio: Jay Pasachoff, Chair of the International Astronomical Union’s Working Group on Eclipses, is Field Memorial Professor of Astronomy at Williams College. He has viewed 55 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 and Chair-Elect of the Historical Astronomy Division of the American Astronomical Society. He received the Education Prize of the American Astronomical Society. Pasachoff is the author of textbooks on astronomy and of the Peterson Field Guide to the Stars and Planets, and co-author of Nearest Star: The Surprising Science of Our Sun and, on a more technical level, The Solar Corona. His research at the transits of Venus of 2004 and 2012 was sponsored by grants from the Committee for Research and Exploration of the National Geographic Society, and he gave an invited lecture on the subject before the American Astronomical Society’s meeting in Anchorage, Alaska, a week after the transit, which he observed with students and colleagues from Haleakala, Maui, Hawaii, at an altitude of 10,000 feet.

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June 5th and June 6th 2012 saw one of the most remarkable and rare astronomical occurrences – a transit of Venus across the face of the sun. Only six of these transits have been seen since Jeremiah Horrocks saw the first one back in 1639, correcting and extending the work of Johannes Kepler, who, with his Rudolphine Tables, had improved the ways of predicting what would happen in the sky.

In any case, nobody alive on earth had seen the transit of Venus before the one in 2004. That turned out to remarkably show Venus’s atmosphere when Venus was only halfway entered onto the sun. And my colleague Glenn Schneider and I, with students and colleagues from Williams College and elsewhere, concentrated our 2012 observations on studying Venus’s atmosphere. We were working also with a group of scientists from France who built nine coordinated coronagraphs – identical instruments that were spread around the world, from as far north as Svalbard and as far south as Australia, to study the arc of Venus’s atmosphere as it appeared above the edge of the sun.

It took about seventeen minutes for Venus to enter the sun this time, and then there’s a six-hour or so interval in which Venus travelled over the center of the sun, and then another seventeen minutes for egress. We were concentrating on the entrance and the egress, as were many people around the world. Some people even took antique telescopes from the 1700’s and 1800’s to see what they could see because there were reports from that period that various scientists discovered the atmosphere of Venus, and my historian of science colleague Bill Sheehan and I had shown that Mikhail Lomonosov, who was usually credited with it, actually didn’t see the atmosphere of Venus because he saw something only for a second or so and we now know that you should be able to see this for twenty minutes. What he described wasn’t at all what we now see.

Anyway, we made many modern observations with our telescopes on the ground. I personally was located with students and colleagues at the ten thousand foot altitude of the Haleakala observatory on a high volcano on Maui in Hawaii, and we were working with another colleague, Kevin Reardon, who was at the Sacramento Peak Observatory of the National Solar Observatory at a nine thousand-plus mountain in Sunspot, New Mexico. His big telescope amounted to a fifty-five thousand millimeter telephoto, giving a very enlarged image, and they had a very advanced set of spectroscopic observations there to record the spectrum in detail —images in various parts of the spectrum of Venus’s atmosphere as it went in. We’re coordinating this with observations made at Venus itself with the European Space Agency’s Venus Express spacecraft and we’ll find out more about Venus’s mesosphere as a result.

Also, there were several spacecraft that observed the sun, and these spacecraft include NASA’s Solar Dynamics Observatory, launched since the previous transit of Venus, and that had two instruments on it: the Atmospheric Imaging Assembly and Helioseismic Magnetic Imager, that gave wonderful high-resolution images of Venus’ atmosphere. And the Japanese Hinode spacecraft, with American participation, had a Solar Optical Telescope (SOT) that gave the highest resolution images of Venus’s atmosphere; and also an x-ray telescope on it showed Venus in silhouette moving across the x-ray corona. And then two NASA spacecraft, the ACRIMsat and the SORCE/TIM instrument, showed the dip in the intensity of the sun by a tenth of a percent that resulted from Venus’s blocking that much of the surface of the sun.

We are interpreting all this in terms of analogies to the many hundreds of exoplanet candidates that have been found by the Kepler spacecraft and by ground-based spacecraft from the transit method. So applying the observations of the transit of Venus, a phenomenon that has been known for a long time, actually has wonderful applications to the most exciting and modern parts of contemporary astronomy, namely the study of exoplanets and the search for their atmospheres.
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365 Days of Astronomy
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