Cal Poly Pomona

Physics and Astronomy Seminar

Thursday, January 17th

Transits of Venus Throughout History

Jay Pasachoff

Williams College

Since Johannes Kepler's predictions of transits of Mercury and Venus in 1631, and observations by Jeremiah Horrocks and William Crabtree of the 1639 transit of Venus, only 6 other transits of Venus have been observed: in 1761 and 1769, 1874 and 1882, and 2004 and 2012. Expeditions were sent all over the world for the 18th and 19th century transits to follow the methods of Halley and others to determine the Astronomical Unit, giving the size and scale of the solar system, arguably the most important problem in astronomy for centuries. I used Huntington Library resources to study the claim on behalf of Mikhail Lomonosov that he discovered the atmosphere of Venus from St. Petersburg at the 1761 transit, which Bill Sheehan and I think we have disproved. We used a fresh translation from the Russian, made at our request by Olga Tsapina, Norris Foundation Curator of American Historical Manuscripts at the Huntington Library. I will also discuss how the infamous black-drop effect bedeviled astronomers in that quest for an accurate A.U., and how Glenn Schneider and I explained the effect through satellite observations of transits of Mercury, showing that it was not simply caused by the Cytherean atmosphere. During the 2004 transit, we detected the 0.1% drop in the Total Solar Irradiance, showing the effect of solar limb darkening, positioning such observations of transits of Venus and of Mercury as analogs to exoplanet transits. Our observations of the atmosphere of Venus with NASA's Transition Region and Coronal Explorer in 2004 led us to plan extensive observations of Venus's atmosphere and other phenomena during the June 5, 2012, transit of Venus, the last to be visible from Earth until 2117. We used NASA's Solar Dynamics Observatory, Hinode, ACRIMsat, and other spacecraft, and ground-based solar telescopes at Sacramento Peak, Kitt Peak, Big Bear, and Haleakala to observe the transit; I will give preliminary reports on these observations during this talk. Further, I will discuss our observations with the Hubble Space Telescope of the September 20 transit of Venus as seen from Jupiter and our use of NASA's Cassini spacecraft to observe the December 21 transit of Venus from Saturn.


Refreshments at 10:50 AM. Seminar begins at 11:00 AM.
Building 8, Room 241
For further information, please call (909) 869-4014

Last modified on Sept 25, 2012
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