For years, astronomers have worried that Betelgeuse might explode. Instead, it’s about to disappear. On Dec. 12th (Universal Time), main belt asteroid Leona will pass directly in front of Betelgeuse, a first-magnitude star in the shoulder of Orion. Millions of people in a narrow path stretching from South Florida to Europe can look up and see the red giant dim or even vanish.

Betelgeuse is not a typical star. Its diameter is 760 times the sun’s, so it appears as a disk 40 milliarcseconds across, much larger than most other stars. High resolution images of Betelgeuse seem to reveal a star in turmoil with giant convection cells bubbling up to the surface. The passage of the asteroid across Betelgeuse may allow astronomers to map these cells and evaluate their role in a possible future supernova explosion. Much is unknown about this occultation. The shape of the asteroid itself is an X-factor. In Sept. 2023, Ortiz and colleagues watched the asteroid occult another star from 17 different locations on Earth. They found that Leona has an oblong shape with dimensions 80 x 55 km, whereas most predictions of the occultation assume the asteroid to be spherical. Leona’s odd shape, plus the fact that it is rotating, could produce some surprises. The occultation path may be wider than expected, and there could be interesting “partial eclipse” effects visible even near the center of the path.

Extremely rare occultation of Betelgeuse