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WILLIAMS COLLEGE—HOPKINS OBSERVATORY
33 LAB CAMPUS DRIVE
WILLIAMSTOWN, MA 01267
Jay M. Pasachoff
Field Memorial Professor of Astronomy
Director, Hopkins Observatory
e-mail: [email protected]
Caltech 150-21, Pasadena, CA 91125
[email protected]
cell phone: 617 285 6351
January 8, 2013
press contact: James Kolesar, Public Affairs Office, Willliams College; [email protected]
science contact: Jay Pasachoff, Caltech 150-21, Pasadena, CA 91125; on sabbatical from
Williams College; [email protected]. Cell phone contact: 617 285 6351
Embargo: until the session begins on Wednesday, January 9, at 10:30 am PST
The three transits of Venus of 2012
Many people around the world thrilled to see a transit of Venus in June (June 5 in the United
States and June 6 in Asia, on the other side of the International Dateline), the dark silhouette of
Venus passing in front of the Sun. Jay Pasachoff of Williams College (Williamstown, MA) and
the California Institute of Technology (Pasadena, CA) and Glenn Schneider (Steward Observatory,
University of Arizona) organized extensive observations of the transit. With support from the
Committee for Research and Exploration of the National Geographic Society, they observed the
six-hours of the transit from the 10,000-foot mountaintop of Haleakala on Maui, Hawaii.
The event was a rare opportunity to see close up, in our own solar system, the type of transit that is
being studied by many scientists around the world using NASA's Kepler spacecraft and groundbased telescopes. Some thousands of these exoplanet transits have been seen. Though it was
widely and correctly said that the 2012 transit of Venus was the last to be seen before the
year 2117, that restriction applies only if you are limited to observing from Earth. The
Pasachoff-Schneider team subsequently organized observations of a transit of Venus that was
occurring if you were on Jupiter on September 20, using NASA's and ESA's Hubble Space
Telescope to observe the reflection of sunlight off Jupiter's clouds. Subsequently, they used
NASA's Cassini mission, in orbit around Saturn, to try to observe the December 21, 2012, transit
of Venus that was occurring if you were on Saturn. The data are still under study for the Jupiter
and Saturn events, and it cannot yet be said whether the attempts to detect the transit succeeded.
Pasachoff, with his colleagues as co-authors, is presenting his team's observations of transits of
Venus as an analog to exoplanet transits at the 221st meeting of the American Astronomical
Society being held on Sunday, January 6th, through Thursday, January 10th, in Long Beach,
California. The scientific paper is scheduled for Wednesday morning, and Pasachoff will
participate in a press conference related to exoplanets on Tuesday morning.
The observations using 14 orbits of the Hubble Space Telescope to study Jupiter, at both
ultraviolet and infrared wavelengths, in September were joint with David Ehrenreich of the
Observatory of Geneva, Switzerland, and Alfred Vidal-Madjar, of the Institut d'Astrophysique in
Paris, France. The observations will be studied with the help of a grant from NASA through the
Space Telescope Science Institute. The observations using the Cassini spacecraft in December
were headed by Philip Nicholson of Cornell, who is on the Cassini team. Each of those transits, at
Jupiter and Saturn, lasted about 10 hours, with a drop in the solar intensity of only a hundredth of a
per cent.
Based on their study of the previous transit of Venus visible from Earth, in 2004, using a NASA
spacecraft as well as their own ground-based observations, Pasachoff and Schneider concentrated
their efforts on studying Venus's atmosphere. It becomes visible as a bright whisker or arc on the
edge of Venus for several minutes before Venus entirely enters the solar disk and after Venus
entirely leaves the Sun.
As part of the team, Kevin Reardon of the National Solar Observatory, then also at the Arcetri
Observatory, Florence, Italy, used the Dunn Solar Telescope on Sacramento Peak, New Mexico, to
observe Venus's atmosphere at high resolution as Venus entered the Sun. From sites in the
continental United States, Venus and the Sun set partway through the transit, so only the opening
phases were observable. These observations were also supported by Pasachoff's grant from the
Committee for Research and Exploration of the National Geographic Society.
Because of the predicted visibility of Venus's atmosphere, Paolo Tanga of the Observatory in Nice,
France, and Thomas Widemann of the Observatory of Paris in Meudon, France, prepared nine
identical telescopes especially to observe Venus's atmosphere at the June 2012 transit. These
telescopes are called coronagraphs, since they block out the everyday solar surface, as do
specialized telescopes for studying the solar corona. One of them was with Pasachoff and
Schneider at Haleakala, where it was operated by Bryce Babcock and undergraduate Muzhou Lu
'13 of Willliams College. It had a blue filter, and its results will be compared with those from the 7
other coronagraphs used photographically, with two each having blue, yellow, red, and infrared
filters, respectively. The ninth coronagraph was used visually by Minnesota historian of science
William Sheehan to detect Venus's atmosphere; Pasachoff and Sheehan have written articles
showing that the reported detection of Venus's atmosphere for the first time at the 1761 transit was
probably not made from the scientist long credited with it, and determining just what could be seen
visually of Venus's atmosphere helps understand the old situation. On Haleakala, Schneider had
brought a small telescope; he and Pasachoff were able to see Venus's atmosphere with their own
eyes looking through it, of course with a suitable safe solar filter, always necessary for looking at
the Sun except during totality of a total solar eclipse (of which Pasachoff and Schneider have each
seen 30, most recently in Queensland, Australia, on November 13/14).
Also at the site with telescopes and electronic cameras as part of the Pasachoff-Schneider team was
Ronald Dantowitz of the Clay Center Observatory (Brookline, MA). His equipment took hundreds
of thousands of short exposures, the rapidity of the images helping counteract the 40 mph winds at
the Haleakala site. The images clearly show the transit and Venus's atmosphere. During the
summer of 2012, undergraduate student Eric Edelman of Wesleyan University, sponsored by the
NSF's student research support for the Keck Northeast Astronomy Consortium, worked at
Williams College with Pasachoff on these and other transit-of-Venus images.
Another major US site for observation was at the New Jersey Institute of Technology's Big Bear
Solar Observatory in California. Vasyl Yurchyshyn of their staff led the observations; Joseph
Gangestad, a Williams College alumnus now at The Aerospace Corporation, represented the
Pasachoff-Schneider group there. The observations with Big Bear's New Solar Telescope showed
not only the atmosphere of Venus very well but also the so-called black-drop effect that delayed
scientists' discovery of the size and scale of the Universe for centuries. Pasachoff, Schneider, and
Leon Golub of the Harvard-Smithsonian Center for Astrophysics explained the cause of the blackdrop effect fully for the first time based on a previous spacecraft observation of a transit of
Mercury, and then observed it at the 2004 transit of Venus. The extensive observations of the
black drop in 2012 will lead to further analysis and confirmation.
The observations of the details of the transit, and the visibility of Venus's atmosphere, showed the
moving parts that go into any transit observation, for planets in our solar system or outside it. Only
about 90% of the dips in stellar brightness observed with the Kepler spacecraft are actually from
exoplanet transits, so it is especially important to understand all the workings of transits. The
closest analog in our own solar system to exoplanet transit observations are made by two NASA
spacecraft that study the Total Solar Irradiance, the total amount of energy received from the Sun
each second on a unit of area at the Earth's average distance from the Sun. Collaborating scientists
who run their respective spacecraft that measure TSI are Richard Willson of ACRIMsat for his
Active Cavity Radiometer Irradiance Monitor 3 instrument, and Greg Kopp of the University of
Colorado for SORCE/TIM (Solar Radiation and Climate Experiment/Total Irradiance Monitor).
They have provided graphs, being shown by Pasachoff in his talk, showing the 0.1% dip in solar
intensity that occurred because of Venus's blocking that tiny bit of the Sun from being visible from
Earth's vantage point.
Coordinated observations during all three transits were made from all possible spacecraft aloft to
study the Sun, so that variations on the Sun itself could be monitored and separated from the effect
of the transit as seen from Earth, Jupiter, and Saturn, respectively. Responsible scientists who
collaborated, coauthors on the paper, include Alphonse Sterling of NASA's Marshall Space Flight
Center and Murray Silverstone of the University of Alabama at Tuscaloosa for the JapaneseAmerican Hinode spacecraft's Solar Optical Telescope; Philip Scherrer and Jesper Schou of
Stanford University for their Helioseismic Imager on NASA's Solar Dynamics Observatory; and
Leon Golub, Patrick McCauley, and Kathy Reeves for data processed from their XRT x-ray
telescope on Hinode. The Atmospheric Imaging Assembly on Solar Dynamics Observatory also
observed the transit. The European Space Agency's Solar and Heliospheric Observatory was so far
toward the Sun from the Earth that no transit of Venus was visible for its instruments.
Much work remains on the data from the three transits of Venus. But there won't be another transit
of Venus visible from Earth until 2117, another transit of Venus visible from Jupiter until 2024, or
another transit of Venus visible from Saturn until 2028. The collaborating scientists will soon
apply for observing time with the Hubble Space Telescope for the 2014 transit of Earth that would
be visible from Jupiter, since it would be exciting to detect Earth's atmosphere in an analogous way
to the current observations of exoplanet atmospheres, and to provide therefore a test of current
methods of observation and analysis.
Web reference and photos: http://www.transitofvenus.info
Paper to be delivered, Wednesday morning, January 9, 2013:
Pasachoff, Jay M., Glenn Schneider, Bryce A. Babcock, Muzhou Lu, Eric Edelman, Kevin
Reardon, Thomas Widemann, Paolo Tanga, Ronald Dantowitz, Murray D. Silverstone, David
Ehrenreich, Alfred Vidal-Madjar, Philip D. Nicholson, Richard C. Willson, Greg A. Kopp, Vasyl
B. Yurchyhyn, Alphonse C. Sterling, Philip H. Scherrer, Jesper Schou, Leon Golub, Patrick
McCauley, and Kathy Reeves, "Three 2012 Transits of Venus: From Earth, Jupiter, and Saturn,"
221st AAS Meeting, Long Beach, CA, January 9, 315.06.
also: Edelman, Eric, Jay M. Pasachoff, Glenn Schneider, Bryce A. Babcock, Muzhou Lu, Kevin
Reardon, Thomas Widemann, Paolo Tanga, and Ronald Dantowitz, 2013, "The 2012 Transit of
Venus: A Closer Look at the Cytherean Aureole," 221st AAS Meeting, Long Beach, 353.04.
Press conference, Tuesday morning, January 8, 2013:
10:30 am, Long Beach Conference Center room 204
The whole press conference: Tuesday, January 8, 2013 -- 10:30 a.m. PST
EXOPLANET SYSTEMS FROM BIRTH TO DEATH
A Planetary System in the Hyades, the Nearest Rich Star Cluster
Ben Zuckerman (Univ. of California, Los Angeles) [309.07]
Exo-Asteroids and Polluted White Dwarfs
John Debes (Space Telescope Science Institute) [220.01, 308.03]
Three Transits of Venus: From Earth, Jupiter, and Saturn
Jay M. Pasachoff (Williams College) [315.06]
Pulsar Planets: Observations and Understanding
Aleksander Wolszczan [424.01]
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