Betelgeuse Is Shrinking

The first direct image of a star other than the Sun, made with the Hubble Space Telescope. Called Alpha Orionis, or Betelgeuse, it is a red supergiant star marking the shoulder of the winter constellation Orion the Hunter.
Credit: Andrea Dupree (Harvard-Smithsonian CfA), Ronald Gilliland (STScI), NASA and ESA

The famous star in the Orion constellation has reduced in size 15 percent over the past 15 years, according to observations from the University of California, Berkeley. Why a red supergiant star would shrink is still unknown.

Scientists speculate that the measurements may be affected by giant convection cells on the star's surface that are like convection granules on the sun, but so large that they bulge out of the surface. However, the star's brightness has not changed significantly, and the star appears to be symmetrical. 

In 1921, Betelgeuse was the first star to have its diameter measured outside the solar system.