WILLIAMSTOWN, Mass., August 5, 1999--Astronomer Jay M. Pasachoff, physicist Bryce Babcock and a team of Williams science students are traveling to Romania for the August 11 solar eclipse, where the chance of weather cooperating is pretty good for eclipse chasing. Pasachoff and his team from Williamstown, Mass. will perform three experiments at the site. This will make 21 central and annular eclipses that Pasachoff has studied.
Two of the three experiments will 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 four million degrees Fahrenheit), even though the everyday surface of the sun below it is only 6,000 degrees Celsius (about 11,000 degrees Fahrenheit).
The first experiment is a search for rapid oscillations in the corona, with periods of about one second. He will use techniques he has developed 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. The experiment is supported by a grant from the Atmospheric Sciences Division of the National Science Foundation.
The second experiment will be to map 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.
Another experiment, in collaboration with Dr. Bryce Babcock, staff physicist at Williams, is in liaison with scientists in charge of an experiment on the Solar and Heliospheric Observatory (SOHO) spacecraft. This 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 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 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 observation is in collaboration with scientists of the Naval Research Laboratory in Washington, D.C. The comparison of the eclipse image with an image taken with a large angle spectrographic coronagraph will provide a calibration of how much light is 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. The experiment is funded by a grant from NASA's Guest Investigator Program for the SOHO spacecraft.
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* Prof. Jay Pasachoff can be reached, August 7 - 12, at 011 40 50 736601 (phone) and by fax at 011 40 50 737760. He is at the Alutus Hotel in Ramnicu Valcea 1000 Romania. The eclipse will happen at 2 p.m., August 11 (Romania), which is 7 a.m. in US EDT. Bucharest time is 7 hours later than Eastern Daylight Time.
* Jo Procter, News Director -- (413) 597-4279
The above story is based on materials provided by Williams College. Note: Materials may be edited for content and length.
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