However, by the late 1980s, iris photometers were superseded by scanning machines which digitized the images and used image processing software to make more precise measurements of stars in crowded fields. The eyepiece was still advantageous in situations like this.” And so good old Helen and her eye and brain were smarter than that machine. The astrophotometer is at the Canada Science and Technology Museum, accession number 2008.0184.001.Ĭlement remembers the light table sometimes having an advantage over more complex technologies, such as an iris photometer in that it enabled the examination of individual stars on ‘messy’ plates stars were close together, as in a globular cluster, shown in the accompanying plate: “…because if the field is too crowded the iris diaphragm picks up other stars in the vicinity and makes a crowded star appear brighter than it really is. Having a negative print is convenient because you can write on it and label the positions of the stars of interest, both the standards and the variables.”Īlso in 1963, Hogg acquired a Cuffey iris astrophotometer, for the measurement and analysis of variable stars, which Clement also used. The chart is a print that looks exactly like the plate, i.e. So someone had already set up a sequence of standards: stars A, B, C, D, E, F, G, which were labelled on an ID chart. The object was to estimate the brightness of the variable stars, but to do that, you have to have standards to compare them with. “I was given a little eye piece, and I had to put it down on the plate and examine the images. Professor of Astronomy Christine Clement remembers being trained to use this table by Hogg as part of research conducted for Hogg in the summer of 1963, just prior to her Master’s degree. She took on teaching duties at the university during WWII and later advanced to full professor in astronomy at the Department of Astronomy at the University of Toronto. She continued her work, including taking the included 1939 plate of the globular cluster M13, while also traveling for her research. Hogg moved to the David Dunlap Observatory in Richmond Hill when her husband received a job there in 1935. This table was used by University of Toronto astronomy professor Helen Sawyer Hogg for the identification and measurement of variable stars.
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