Pasachoff lectures on solar eclipses, research

This year’s faculty lecture series continued on Feb. 10 with a presentation by Field Memorial Professor Astronomy and chair of the astronomy department Jay Pasachoff on his work observing solar eclipses. The lecture in Brooks-Rogers Auditorium attracted approximately 60 students, professors and members of the Williamstown community.

Assisted by a series of slides, Pasachoff described his research in solar eclipses and his past trips all over the world, many of which have included students, to study the phenomenon.

Professor Pasachoff’s specialty is studying the solar corona, a region of superheated gas which surrounds our sun. Unlike most hot objects, whose temperature decreases as one moves away from them, the region around the sun actually grows hotter. The surface of the sun is only 6000 Kelvin, but the corona, which extends far out into space, can be up to four million Kelvin.

One of the big questions for astronomy, said Pasachoff, is how all that heat is transferred to the corona, since ordinary means of heat transport (radiation and convection, for example) could not transfer that much heat that quickly from the cooler regions beneath the corona.

As Pasachoff described, however, studying the corona is harder than one might think. Despite its high temperature, the corona is not nearly as luminous as the main body of the sun, and without being able to see the light from it, scientists cannot study it.

Fortunately, every 18 months or so, there is a total solar eclipse, when the moon passes between the sun and the earth and casts a shadow on the earth’s surface. For a few minutes, the main portion of the sun is obscured, and with the sky appearing one million times darker than normal, the faint solar corona can be observed.

With grant money from places like the National Science Foundation and National Geographic, Pasachoff is able to examine the corona in close detail and learn more about it, frequently correlating his results with NASA.

Complete solar eclipses do not always occur right over the Purple Valley, though, and so Pasachoff travels to see them. Pasachoff described his most recent expedition this past summer, to view the Aug. 11, 1999 total eclipse near Bucharest, Romania, where he brought several students, faculty and alumni to help him make observations.

Two weeks before the eclipse, the team members arrived and began setting more than a ton of equipment on the roof of a hotel in Ramnicu Valcea, a small city in the center of the eclipse path, well away from the pollution of a large city like Bucharest but still within reach of all the facilities needed.

Telescopes had to be aligned and calibrated, computers set up, programs tested and of course, cameras of all sorts prepared to immortalize the event. The day dawned slightly cloudy, but by the time of the eclipse, the sky was perfectly clear, and the research team had an excellent view for all of the two minutes and 23 seconds of totality. They returned happy with masses of data which are still being analyzed.

According to Pasachoff, some of the data they gathered is being shared with the Solar and Heliospheric Observatory (SOHO), which can gather information about the outer corona all the time, by creating artificial eclipses with an occulting disk much larger than the size of the moon.

SOHO is unable to create a good image of the inner corona without scattering light and thus ruining the value of the data, so it coordinates with scientists such as Pasachoff during solar eclipses to create composite images of the corona.

This summer’s expedition was especially interesting, said Pasachoff, because it fell near the peak of the 11-year sunspot cycle.

Sunspots are magnetic phenomena, darker, cooler places on the sun’s surface, but they are associated with solar flares, explosions of hot gas which follow magnetic field lines out of the sun.

According to Pasachoff, the data gathered by the Williams team was exciting not only for its magnitude, but also because it helped support current theories on how the corona reaches such high temperatures.

The most widely accepted theory is that magnetic fields provide the energy to transport the heat, and as Pasachoff showed, the team was able to correlate particularly hot, active locations in the corona with sunspot regions on the solar surface, using images gathered by other researchers. Sunspots are known to be regions of high magnetic activity, so the correlation helps lend more credence to the theory.

Team members agreed that the trip was fun as well as useful. According to Joey Shapiro ’01, “It was a really good, fun experience to be on a scientific expedition doing research in Romania.”

Still, some might say, why go through with it? Sure, if you have to travel to Aruba in February, as one expedition did in 1998, it might not be too bad. But sometimes an eclipse will occur in a not-so-accessible place, like Inner Mongolia.

For Pasachoff, the answer lies in the universality of what he studies.

As he puts it, “There are billions of other stars like our sun, so when we understand it we’ll be able to understand other stars too.” And once we understand how all the stars in it work, we are a bit further along on the path of understanding the nature of the universe.

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