When the moon's elliptical orbit around the Earth takes it directly between the sun and Earth, it blocks out all or part of the sun, depending on the Earth's distance from the sun. Total eclipses happen, on average, every 1.5 years. The last one was June 21, 2001.
In Ceduna, where Pasachoff and his colleagues will be, totality will last for 34 seconds and the sun will be only 9 degrees above the horizon, making for what many are calling a sunset eclipse.
"Having the sun only 9 degrees from the horizon will enable some photos including the sun and the horizon on the same frame with a bigger image of the sun than previously possible," said Pasachoff.
While some astronomers are excited for the sunset spectacle afforded by this eclipse, Pasachoff says that it will make scientific experiments more difficult because sunlight will have to pass through so much of the atmosphere.
The experiments to be conducted by the Williams team in Ceduna build on experiments conducted on previous Williams College eclipse expeditions to the 1998 total eclipse in Aruba, the 1999 total eclipse in Romania, and the 2001 total eclipse in Zambia.
The first of their experiments is to search the corona for high-frequency solar oscillationsrapid vibrations. Some theoretical models hold that these vibrations enable the corona to reach a temperature of 2 million degrees Celsius (3.6 million degrees Fahrenheit) while the surface of the sun is about 6,000 degrees Celsius (11,000 degrees Fahrenheit).
Using observational data gathered during the 1999 eclipse expedition, Pasachoff and colleagues published a paper in the June 2002 issue of Solar Physics on the detection of coronal oscillations, verifying a set of theories on coronal heating through magnetic waves.
"There are theoretical predictions by other astronomers about models of coronal heating and I, as an observational observer, look for observational tests of those models," explained Pasachoff.
In another experiment, the astronomers will map the coronal polarization to help determine how much sunlight reaches Earth from the corona.
Pasachoff says that sunlight reaches Earth from the corona from three different sources: light actually emitted from the corona; light from the sun that is reflected off coronal electrons towards Earth; and light added to that light from the reflection of dust particles near the orbit of Mercury.
"This third source is not really from the corona, though it appears as such during the eclipse, and it is not polarized," said Pasachoff. "So measuring the polarization enables us to figure out how much of what we see is actually coming from the sun."
In a third experiment, the astronomers will take high-resolution images of the inner and middle corona to bridge the gap between regions observed by NASA's Solar and Heliospheric Observatory spacecraft.
A full image of the corona will allow astronomers to trace the coronal streamers that they see in the outer and middle corona to the streamers' roots on the sun's surface and to see the region of the corona where the solar winds form, said Pasachoff.
Spectators such as Staiger have no scientific agenda for viewing this eclipse other than amateur photography. However, the eclipse-chaser is already discussing plans for what he calls "the ultimate eclipse chase" to view the November 23, 2003 event in Antarctica.
"When the eclipse will occur next year in Antarctica, I want to be among an emperor penguin rookery and watch their reaction as sudden darkness occurs five months before the expected nightfall," he said.
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