Astronomy: Chance capture of Betelgeuse’s dimming by weather satellite

The so-called Great Dimming of the bright red supergiant star, Betelgeuse, was serendipitously captured by a weather satellite known as Himawari-8. The observations — presented in a paper published in Nature Astronomy — suggest that the dimming was caused by a combination of the star cooling and dust condensing nearby.

Betelgeuse — a red supergiant star in the Orion constellation — dimmed visibly in late 2019 and early 2020, reaching a historical minimum of brightness and creating an expectation that it might imminently explode as a supernova. Many of the most powerful astronomical telescopes tracked the dimming. So did Himawari-8, a Japanese weather satellite that normally tracks the Earth’s weather patterns from orbit using optical and infrared light.

Realizing that Betelgeuse might have occasionally been captured in the background of Himawari-8’s images of the Earth, Daisuke Taniguchi and colleagues pieced together four and a half years of observations, including the six months when Betelgeuse dimmed. The optical and infrared wavelengths of light that the satellite normally detects were ideal for studying the dimming. The satellite’s location outside of the Earth’s atmosphere also meant that it could record infrared light that the atmosphere might normally block. The authors suggest that Betelgeuse’s dimming was caused both by the star cooling by approximately 140 degrees Celsius, and by dust condensing from warm gas around it, in almost equal proportions. These conclusions support those from ground-based telescope observations.

The authors also collected data on four other stars over the same time period, suggesting that meteorological satellites like Himawari-8 could be valuable astronomical resources. This, they propose, is because they overcome some of the limitations of ground-based observatories, such as offering the potential for more frequent observations.