Research Interests

Coronal Heating


Jay M. Pasachoff specializes in studying the sun at total solar eclipses.  He and his colleague study coronal dynamics and 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 65 previous eclipse expeditions, and with a large group of colleagues and students from Kastellorizo, Greece, in 2006; from Akademgorodok, Siberia, in 2008; from Tianhuangping, China, in 2009; from Easter Island, in 2010; from Australia, in 2012; from Gabon, in 2013; from Svalbard, in 2015; and in Ternate, Indonesia, in 2016; with the 2017 American eclipse planned at this posting.

He integrates his 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., with the SWAP images on the PROBA2 spacecraft of the European Space Agency (in collaboration with Dan Seaton ’01), and forthcoming with GOES-16 (again with Seaton).  As Chair of the International Astronomical Union’s Working Group on Solar Eclipses, Pasachoff supervises Websites at and

At this posting, Pasachoff has arranged a massive expedition to Salem, Oregon, for the August 21, 2017, total solar eclipse, including 8 undergraduates and many alumni in addition to scientific colleagues.  The expedition is supported by grants from the Solar Terrestrial Program of the Atmospheric Sciences Division of the NSF and from the Committee for Research and Exploration of the National Geographic Society.  Additional students and alumni are supported by grants from the Massachusetts NASA Space Grant Consortium, the Sigma Xi society, and the Clare Booth Luce foundation.


Occultations by the Outer Planets and Their Moons


Drs. Pasachoff, formerly with Steven Souza and  Bryce Babcock, and with his students work closely with Michael Person and Amanda Bosh of MIT and Amanda Sickafoose of the South African Astronomical Observatory and MIT on occultations of stars by objects in the outer solar system, a collaboration begun with the late James Elliot. 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, recently with observations from 2015 taken with the 1-m and other telescopes at Canterbury University Mt. John Observatory in New Zealand, less than two weeks before the flyby of Pluto and Charon by NASA’s New Horizons spacecraft.

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


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; Ph.D. Ohio State, 2013; now a Hubble Fellow at the Harvard-Smithsonian Ceter for Astrophysics) 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 (Ph.D., Boston U.; Jack Eddy Fellow at the Harvard-Smithsonian Center for Astrophysics) and earlier La Palma observations made with David Butts ’06 (Ph.D. MIT Aeronauts and Astronautics; now on staff of MIT Draper Laboratory) and Joseph Gangestad ’06 (Ph.D. Purdue U.; at Aerospace Corp.).

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 was supported by a grant from NASA through the Smithsonian Astrophysical Observatory.

Megan Bruck ’07, Ph.D. from Brown, now on the staff of Lawrence Livermore Laboratory working on killer asteroids, 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, got her Ph.D. 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 was a graduate student in planetary sciences at MIT and has gone into an energy company.

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 applied 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.

Pasachoff, Babcock, Schneider, and Ron Dantowitz, with students, observed the 2012 Transit of Venus with colleagues and students from the top of Haleakala, Maui, Hawaii, alongside the Mees Solar Observatory.
Pasachoff, Schneider, Robert Lucas, and Evan Zucker observed the May 9, 2016, Transit of Mercury from the Big Bear Solar Observatory, California.  A first paper appeared: Pasachoff, Jay M., Bernd Gährken, and Glenn Schneider, 2017, “Using the 2016 transit of Mercury to find the distance to the Sun,” The Physics Teacher, 55, #3 (March): cover illustration plus article.

Primordial Deuterium Abundance

Pasachoff also has long studied cosmic deuterium and its relation to cosmology, in recent years in collaboration with Donald Lubowich of Hofstra University. 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 Donald Lubowich, used 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 also obtained observations in the direction of the star iota Herculis and of the Orion Nebula at the Kitt Peak National Observatory.  They worked 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, now needed rejuvination.

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.  They have subsequently presented other papers at INSAP meetings and in journals, including Pasachoff, J. M., and R. J. M. Olson, 2014, “Art of the Eclipse,” Nature 506, 17 April 2014, cover and pp. 314-5,; and Pasachoff, J. M., and R. J. M. Olson, 2015, “The 1918 Eclipse Mural Series by Howard Russell Butler for the American Museum of Natural History and the Hayden Planetarium
,” in Inspiration of Astronomical Phenomena VIII: City of Stars,, edited by B. P. Abbott (San Francisco: Astronomical Society of the Pacific), Astronomical Society of the Pacific Conference Series, vol. 501.

Pasachoff and Olson are continuing their collaboration with an illustrated book to be tentatively entitled Heavens Above, to be published by Reaktion Press, London, in 2018 or 2019.
Pasachoff and Olson are advising curator Stephen Nowlin of the Willliamson Gallery of Art Center College of Design in Pasadena, CA, for an eclipse/art/artifacts exhibition during summer 2017.