Measuring Betelgeuse’s Unexpected Dimming With U and B Filters

Student: Connor Bronson-Doherty

Mentor: Cassandra Fallscheer


The red supergiant star, Betelgeuse, was first reported to be dimming beyond its usual fluctuations in October 2019. Since then, many professional and amateur members of the astronomy community have been observing the star, analyzing the data, and trying to determine the cause of its dimming. From 28 January to 27 February 2020 we observed Betelgeuse using the CWU 0.6-meter research telescope with Bessel Blue and Ultraviolet filters. Our magnitude data were submitted to the American Association of Variable Star Observers’ (AAVSO) database where we found our magnitude trends to be consistent with the trends from other submissions while exhibiting a slight offset in actual values. Our data, along with other AAVSO data submissions, and recent findings by other AAVSO partners have found that Betelgeuse has ceased dimming and is slowly rising in magnitude in line with its variable cycle putting some theories to rest but creating even more questions as to why Betelgeuse exhibited the anomalous dimming behavior.


2 thoughts on “Measuring Betelgeuse’s Unexpected Dimming With U and B Filters”

  1. Hi Connor, It is kind of hard to see your figure on my screen and it doesn’t look like I can download your poster. Can you explain what the different colors are? Which points are your data? Is it possible to determine uncertainty for measurements like this? How might one go about doing that?

    1. Hello Dr. Snowden,

      I’m sorry I didn’t provide a means to download the poster. I don’t know how the site feels about posting links in the comments so I will refrain from doing so at the moment. If you would like a copy of the poster just let me know and I can email it to you.

      The different colours and shapes of each magnitude data point represent the different filters that were used during observation. We observed using Johnson Blue and Ultraviolet filters which are represented by the solid dark blue stars and light blue ovals respectively. Our data points are indicated by the lines connecting them to the boxes containing their corresponding data. It is also possible to go to the AAVSO website, search for their Betelgeuse magnitude curve, and search for our data using the observer code “BCOB.”

      As for the uncertainty, there is a lot we did not account for. Dr. Landolt includes error values in his equatorial standards charts that we did not include in our data reduction process. We also didn’t take into account atmospheric extinction or the amount of error that might result from our extremely short exposer times. The error from the Landolt charts should be simple enough to include in our calculations, but I’m still learning how to account for atmospheric extinction so I sadly can’t say much about how to apply that at the moment.

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