with instructor Tom Calderwood. Originally broadcast June 4, 2022. Astronomers have spent decades defining photometric "systems." Systems like Johnson-Cousins define a standard scale on which photometry from different observers can be directly compared. However, simply using a Johnson or Cousins filter does *not* put your magnitudes on the standard system. Your data require adjustment, and this step is known as transformation. In this discussion, Tom explains why transformations are necessary, and sketch out the basics of how their parameters are determined.
Tom Calderwood is head of the AAVSO Photoelectric Photometry Observing Section. He observes from Central Oregon, and is the author of "The Great Dimming of Betelgeuse" in the March 2021 issue of Sky & Telescope. A graduate of MIT in mathematics, he is a retired software engineer who worked on parallel processing computers, communication networks, video games, and the data system for the Chandra X-ray Observatory.
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