News Release

Scientific experiments at the August 11 eclipse: The Williams College expedition

Peer-Reviewed Publication

Williams College

WILLIAMSTOWN, Mass., August 5, 1999--When the sun is covered by the moon on August 11, a group of Williams College faculty and students will be in Romania to study the eclipse. The research team is headed by astronomer Jay M. Pasachoff

The expedition is supported by grants from NASA's Guest Investigator Program for the Solar and Heliospheric Observatory spacecraft, from the Committee for Research and Exploration of the National Geographic Society, and from the Atmospheric Sciences Division of the National Science Foundation.

Pasachoff is preparing his observations for a site at the peak of the eclipse, which will cross Europe with weather forecasts improving eastward to the point of maximum eclipse, which occurs about two hours' drive northwest of Bucharest.

The expedition has brought with it about 3000 pounds (a ton and a half) of telescopes, optics, computers, and other equipment, and is located at Ramnicu Valcea, about 170 km west of Bucharest.

Two of the experiments deal with the still open question of how the corona, the outermost layer of the sun's atmosphere, can reach a temperature of two million degrees Celsius (about 4 million degrees Fahrenheit), even though the everyday surface of the sun below it is only 6,000 degrees Celsius (about 11,000 degrees Fahrenheit). A third experiment is in liaison with scientists in charge of an experiment on the Solar and Heliospheric Observatory (SOHO) spacecraft. The experiments are in collaboration with Dr. Bryce Babcock, staff physicist at Williams College.

The observations are possible only during the brief minutes of a total solar eclipse, when the everyday sun is hidden by the moon, allowing the faint corona to be observable from earth. On ordinary days, the corona is hidden by the blue sky, since it is about a million times fainter than the layer of the sun we see shining every day, the photosphere.

The first experiment is a search for rapid oscillations in the corona, with periods of about one second. Pasachoff and his colleagues have developed techniques over the last two decades to observe in the so-called "coronal green line," a color in which the corona emits light especially strongly, with time resolution so fast that such short periods can be detected. Oscillations with periods in that short range are predicted by some theories that hold that the extreme coronal heating is caused by vibrations of magnetic loops. The loops of gas, held in place by the sun's magnetic field, have been observed, and the question is whether their vibrations bring enough energy into the corona to heat it sufficiently. One of the sites at which they will look on the edge of the sun will be the one that NASA's Transition Region and Coronal Explorer spacecraft, on which Golub is a principal investigator, is imaging at extremely high resolution at the time of the eclipse. The experiment is supported by a grant from the Atmospheric Sciences Division of the National Science Foundation.

The second experiment is a map of the temperature of the corona, using a technique of comparing electronic images of the corona taken at special ultraviolet wavelengths. Following theoretical work, these wavelengths are chosen to include two such at which the difference between the shape of the everyday sun's spectrum and the corona's spectrum is especially striking. The experiment is supported by grants from the Committee for Research and Exploration of the National Geographic Society.

The third experiment is to image the solar corona during the eclipse to compare with observations of the corona seen with the Extreme-ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO), in collaboration with scientists at NASA's Goddard Space Flight Center. The features seen at the eclipse outside the solar disk will be matched up with their bases seen on the disk with the EIT experiment. Further, the experiment uses a lens that gives an image at the same scale and with a green filter that matches a filter in one of the telescopes in the coronagraph system on SOHO; this telescope was operable during the 1998 eclipse though is no longer working. This observation was in collaboration with the late Dr. Guenter Brueckner of the Naval Research Laboratory in Washington, D.C., principal investigator of that experiment, LASCO (Large Angle Spectrographic Coronagraph), and is now in collaboration with other scientists at NRL. The comparison of the eclipse image with an image taken with one of LASCO's coronagraphs will provide a calibration of how much light was scattered in the process of making an artificial eclipse on board the spacecraft. Such artificial eclipses cannot quite match the quality of a natural eclipse, in which the moon hides the sun's light before it reaches a telescope. Stephan Martin of Williams College is the collaborating staff member. The experiment is funded by a grant from NASA's Guest Investigator Program for the SOHO spacecraft.

Pasachoff is Field Memorial Professor of Astronomy, chair of the astronomy department, and director of the Hopkins Observatory at Williams College. He is also chair of the Working Group on Eclipses of the International Astronomical Union. He is the author of the Peterson Field Guide to the Stars and Planets in addition to astronomy texts. Scientific staff also includes Dr. Bryce Babcock of Williams College; Lee Hawkins of Wellesley College; Stephan Martin of Williams College; and Jonathan Kern, Optics Scientist at the Laser Interferometer Gravitational-Wave Observatory of Caltech.

###

Press contacts:

Jo Procter, news director, phone 413-597-4279

Prof. Jay Pasachoff: Saturday, August 7-August 12 in Ramnicu Valcea: Alutus Hotel Ramnicu Valcea 1000 Romania, phone from US: 40-50-736601; fax from US: 40-50-737760


Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.