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Africa: Eclipse Diary 3
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19 June 2001
Posted to the web 19 June 2001
Roban Hultman Kramer
Lusaka, Zambia
AllAfrica has been following preparations for scientific observation of the June 21, 2001 solar eclipse by a team of astrophysicists from Williams College in the United States. Among the group are nine Williams students plus the author of our eclipse diaries, a student from Swarthmore College, at Williams as a Keck Northeast Astronomy Consortium Summer Fellow.
Lusaka, Zambia
We have really started the intensive setup work now. Everyone is very busy, and each experiment is encountering different challenges. I am working with Shoshana Clark, who has just graduated and is on her way to Stanford University, on an experiment related to the temperature of the corona. We are supervised by Lee Hawkins, a scientist from Appalachian State University
Yesterday we began writing the computer scripts that will automate image taking and filter-wheel control during the eclipse. The filter wheel and CCD camera are actually controlled by two separate computers, so Shoshana has been writing filter-wheels scripts in Qbasic, while I work on the CCD control script in Visual Basic on another machine.
Yesterday Peter Smith from the Harvard-Smithsonian Center for Astrophysics visited us to discuss some measurements we are making for him. There is a discrepency in the polarization of the corona measured by two instruments aboard the SOHO spacecraft, and we hope to be able to resolve that by making our own measurement. Dr. Smith came to talk to us about the best way to do our observations for comparison with both SOHO instruments.
We came up with an observation plan to fill the three minutes of totality and to have the best chance of getting useful images. The task is complicated by the variation in brightness of the corona depending upon its distance from the sun. We need the limb of the eclipse [at the sun's edge] in our picture, so that we know what part of the corona we are seeing.
But the inner corona is several hundred times brighter than the part we need to observe. We will end up overexposing the part of the image near the sun, in order to get enough information for our analysis, so we have to orient the CCD camera so that the overexposure has the least chance of affecting our measurments.
Today Shoshana and I have been testing our scripts. We've placed labeled disks in our filter wheel and have run through the scripts multiple times to make sure we have the proper sequence of exposures through each combination of filters and polarizers. Tonight we will be taking test images of stars and the planet Mars to check for any instrumental polarization.
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Eclipse Diary, Part 1 | Eclipse Diary, Part 2
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