                        Astronomy Picture of the Day

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                               2021 October 9

                         50 Light-years to 51 Pegasi
                 Image Credit & Copyright: Josselin Desmars

   Explanation: It's only 50 light-years to 51 Pegasi. That star's
   position is indicated in this snapshot from August, taken on a hazy
   night with mostly brighter stars visible above the dome at Observatoire
   de Haute-Provence in France. Twenty-six years ago, in October of 1995,
   astronomers Michel Mayor and Didier Queloz announced a profound
   discovery made at the observatory. Using a precise spectrograph they
   had detected a planet orbiting 51 Peg, the first known exoplanet
   orbiting a sun-like star. Mayor and Queloz had used the spectrograph to
   measure changes in the star's radial velocity, a regular wobble caused
   by the gravitational tug of the orbiting planet. Designated 51 Pegasi
   b, the planet was determined to have a mass at least half of Jupiter's
   mass and an orbital period of 4.2 days, making it much closer to its
   parent star than Mercury is to the Sun. Their discovery was quickly
   confirmed and Mayor and Queloz were ultimately awarded the Nobel Prize
   in physics in 2019. Now recognized as the prototype for the class of
   exoplanets fondly known as hot Jupiters, 51 Pegasi b was formally named
   Dimidium, latin for half, in 2015. Since its discovery, over 4,000
   exoplanets have been found.

                  Tomorrow's picture: full moon silhouettes
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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