The variable red supergiant star Betelgeuse dimmed from its usual apparent magnitude of 0.1–1 during the period from November 2019 to March 2020. In particular, during 7–13 February 2020 its visible brightness reduced to an apparent magnitude of 1.6. Miguel Montargès and his colleagues report high-angular-resolution observations of Betelgeuse that resolve its surface. They find that the southern hemisphere was an order of magnitude darker than usual. They attribute this to two related causes: 1) a cool spot, and 2) formation of dust over the cool spot.
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