Research Interests

Coronal Heating

Jay M. Pasachoff specializes in studying the sun at total solar eclipses, working closely with Drs. Steven Souza and Bryce Babcock. They carry out experiments to study the million-degree-temperature of the solar corona in order to find out how the corona gets so hot.  Their work has been supported by the National Geographic Society, the National Science Foundation, and the Keck Northeast Astronomy Consortium.

See for images and discussions of his 50 previous eclipse expeditions, and with a large group of colleagues and students from Kastellorizo, Greece, in 2006; from Akademgorodok, Siberia, in 2008; and from Tianhuangping, China, in 2009.

Drs. Pasachoff, Souza, and Babcock carried out an extensive expedition to Kastellorizo, in the Greek Dodecanese islands, for the March 29, 2006, total solar eclipse. They included a half dozen astrophysics and astronomy majors. Drs. Pasachoff and Babcock had similar expeditions to Siberia for the August 1, 2008, total solar eclipse and to China for the July 22, 2009, total solar eclipse, also including Williams College students. Pasachoff's 2010 total eclipse expedition, with two students, was to the eclipse of 11 July on Easter Island in mid-Pacific.

They again integrated their ground-based eclipse observations with images from the Solar and Heliospheric Observatory (SOHO) spacecraft, a joint venture of NASA and the European Space Agency, and, newly, with NASA's Solar Dynamics Observatory. As Chair of the International Astronomical Union's Working Group on Solar Eclipses and of a Program Group on Public Information at the Times of Eclipses, Pasachoff supervises Websites at and

Occultations by the Outer Planets and Their Moons

Drs. Pasachoff, Souza, and Babcock and their students have been working closely with Drs. James Elliot and Michael Person of MIT and Amanda Gulbis of the South African Astronomical Observatory and MIT on occultations of stars by objects in the outer solar system. Their 2002 observations of an occultation of a star by Pluto showed that Pluto's atmosphere is undergoing global warming. Their 2005 observations of a rare occultation of a star by Pluto's moon Charon improved measurements of Charon's diameter and density and set new limits on Charon's atmosphere. They have continued monitoring Pluto's atmosphere, which has leveled off its temperature variation, most recently with observations from 2008.

Their work is supported by a grant from NASA, and they use electronic cameras purchased on a previous NASA grant.

Joseph Gangestad '06 worked on the Charon occultation and wrote his senior thesis on this and other occultation topics. Adam McKay '08 worked on a Pluto occultation and wrote his senior thesis on it and other observational topics.

Pasachoff, Souza, and Babcock extended their occultation observations beyond Pluto by studying, again jointly with MIT and other colleagues, the occultation of a Kuiper-belt object in 2009. Katie DuPré '10 joined in the observing expedition to Hawaii and included results in her senior thesis.

Solar Chromospheric Structure

Pasachoff and students observed the solar chromosphere, the middle layer of the solar atmosphere, in high resolution using simultaneously the 1-m Swedish Solar Telescope on La Palma in the Canary Islands and NASA's Transition Region and Coronal Explorer (TRACE) spacecraft. They worked in collaboration with Drs. Leon Golub and Ed DeLuca of the Harvard-Smithsonian Center for Astrophysics and with scientists from the Lockheed Martin Solar and Astrophysics Laboratory.

Their work was supported by a research grant from NASA in the Guest Investigator Program for TRACE.

Owen Westbrook '06 and Jennifer Yee (Keck Northeast Astronomy Consortium Summer Fellow, Swarthmore '07) worked with Pasachoff in Williamstown and at the Roque de los Muchachos Observatory on La Palma.  Westbrook continued the project as his senior thesis.  They continued work that involved the senior thesis of Kamen Kozarev '05 and earlier La Palma observations made with David Butts '06 and Joseph Gangestad '06.

The results of the Canary Islands spicule studies, related to studies from NASA's Transition Region and Coronal Spacecraft, were included in the senior thesis of Will Jacobson '08, and appeared in print, jointly with Alphonse Sterling of NASA, as:
Pasachoff,. Jay M., William A. Jacobson, and Alphonse C. Sterling, 2009, "Limb Spicules from the Ground and from Space," Solar Phys., 260, #1, 59-82. arXiv astro-ph 0909.0027; DOI 10.1007/s11207-009-9430-x

X-ray Observations of Stellar Coronas

Pasachoff and his students worked with Drs. Nancy Evans and Scott Wolk of the Harvard-Smithsonian Center for Astrophysics on studying x-ray observations of galactic star clusters made with the Chandra X-ray Observatory.  The observations began with the double cluster h and chi Persei. 

The work is supported by a grant from NASA through the Smithsonian Astrophysical Observatory.

Megan Bruck '07 worked on the project in Williamstown and Cambridge and continued her summer work as an Independent Study course. She worked after graduation as a research assistant in x-ray astronomy at the Harvard-Smithsonian Center for Astrophysics, and is a graduate student in planetary sciences at Brown University.

Westbrook worked on related projects with these colleagues at the Harvard-Smithsonian Center for Astrophysics during 2006-8. He is a graduate student in planetary sciences at MIT.

Transits of Venus and Mercury

Pasachoff has been investigating transits of Mercury and Venus, using ground-based observations and observations from NASA's Transition Region and Coronal Explorer (TRACE).  His work has been in collaboration with Glenn Schneider of the Steward Observatory, University of Arizona.  Their analysis of a transit of Mercury across the face of the sun led to an explanation of the long-questioned black-drop effect.  They are applying their analysis to the observations from TRACE and from the Williams College Transit of Venus Expedition to Thessaloniki, Greece, which was carried out in collaboration with Drs. Souza and Babcock.  This transit on June 8, 2004, was the first transit of Venus visible since the year 1882, and was therefore much anticipated.  See the special Williams website at for information about current and past transits.  Pasachoff and Suranjit Tilakawardane '07 observed the transit of Mercury in November 2006 from Haleakala, Maui, Hawaii. Bryce Babcock, working also with Kevin Reardon '92, who is now at the Arcetri Observatory in Italy, used one of our electronic cameras to observe the transit of Mercury from the Sacramento Peak Observatory of the National Solar Observatory, Sunspot, New Mexico.

The Williams College Transit of Venus Expedition included Pasachoff, Babcock, David Butts '06, Joseph Gangestad '06, Owen Westbrook '06, Alan Cordova '06, Kayla Gaydosh (Keck Northeast Astronomy Consortium Summer Fellow, Bryn Mawr '05), and Rob Wittenmyer '98.  They worked in Greece in collaboration with Prof. John Seiradakis of the Aristotelian University of Thessaloniki.  Dr. Souza observed the transit from Williamstown.

Pasachoff and Schneider also worked with Dr. Richard Willson of Columbia University with observations of the total solar irradiance as observed from Willson's ACRIMsat, a spacecraft that measures what used to be called the solar constant.  Their observations of Venus's effect has applications to future transit observations of the newly discovered exoplanets, planets orbiting other stars.

Primordial Deuterium Abundance

Pasachoff also studies cosmic deuterium and its relation to cosmology. Theory shows that all the deuterium (heavy hydrogen) in the Universe was formed in the first 3 minutes after the big bang; studies of the current distribution of deuterium in our Milky Way Galaxy can lead to an evaluation of the density of matter in the Universe and thus whether the Universe has enough gravity to eventually cease its expansion. Pasachoff and students, along with colleague Donald Lubowich of the American Institute of Physics, have been using telescopes at the Kitt Peak National Observatory and the National Radio Astronomy Observatory to study deuterium in galactic stars and in the Sagittarius A radio source at the center of our galaxy.  They have also obtained observations in the direction of the star iota Herculis and of the Orion Nebula at the Kitt Peak National Observatory.  They are working with Prof. Tom Millar of the University of Manchester on explaining various deuterium molecular observations with chemical interstellar models.

Terry-Ann Suer '05 worked on various stages of the project and set up a Web page with historical papers at

Images of Comets in Art

Prof. Pasachoff works with Prof. R. J. M. Olson of the New-York Historical Society, Professor Emerita of Art History at Wheaton College, to study the relation of art and astronomy.  They began with a study of images of comets in 18th and 19th century British art and the growth of scientific accuracy in artistic representation. On twin grants from the Getty Foundation, as Getty Fellows they wrote a book about the subject, which involved research in London, Cambridge, and Edinburgh at the Royal Society, the Royal Astronomical Society, the Royal Observatories in Greenwich, Edinburgh, and Cambridge, the British Museum, the Tate Collection, and elsewhere. The book was published as Olson and Pasachoff: Fire in the Sky: Comets and Meteors, the Decisive Centuries, in British Art and Science (Cambridge University Press, hardback 1998; paperback, 1999).  Students participated in a Winter Study course in England recreating many of the research sites.

Pasachoff and Olson gave an invited paper about comets in science and art in early Renaissance Italy at the meeting of the Division of Planetary Sciences of the American Astronomical Society in Padua, Italy.  They subsequently gave a paper about astronomy in the Medician Court at a meeting of the College Art Association in Seattle.

Pasachoff and Olson studied a painting in a Bavarian abbey showing St. Benedict viewing a total solar eclipse. See 2007, "St. Benedict Sees the Light: Asam's Solar Eclipses as a Metaphor," Religion and the Arts 11, 299-329. ( Also

They subsequently discussed comets in art at a European Space Agency comet workshop in Brussels.

Pasachoff and Olson gave a paper about solar eclipses in art history at the 6th meeting on The Inspiration of Astronomical Phenomena held in Venice, Italy, in 2009. They plan a paper about Caroline Herschel, and the eight or more comets she discovered during the 1790's, at the 7th meeting on The Inspiration of Astronomical Phenomena held in Bath, England, in 2010.