Free Astronomy Magazine January-February 2019

PLANETOLOGY 5 JANUARY-FEBRUARY 2019 A little over a century ago, the American astronomer Edward Emerson Barnard, already famous for having discovered fifteen comets, measured the proper motion of a star of magnitude 9.5 in the con- stellation of Ophiuchus, obtaining a surprising value: 10.3 arcseconds per year. Barnard had discovered the fastest star in the night sky, so fast that it covers an angle the size of the full moon in 180 years. Usually, the more an object appears to move quickly in the sky, the closer it is to the observer, and, in fact, that star is only 6 light years away. Only the components of the Alpha Centauri triple system are closer to the Sun. T he nearest single star to the Sun hosts an exo- planet at least 3.2 times as massive as Earth — a so- called super-Earth. Data from a worldwide array of tele- scopes, including ESO’s planet-hunting HARPS instru- ment, have revealed this frozen, dimly lit world. The newly discovered planet is the second-closest known ex- oplanet to the Earth and or- bits the fastest moving star in our night sky. This image shows an artist’s impression of the planet’s surface. [ESO/M. Kornmesser] On the right, a video from the ESOcast Light series in- troducing the discovery of Barnard’s Star b. [ESO]