Astronomy Picture of the Day

   [1]Discover the cosmos! Each day a different image or photograph of our
      fascinating universe is featured, along with a brief explanation
                    written by a professional astronomer.

                                 2022 May 3
    [2]The featured image shows the planet Mercury below the star cluster
    Pleiades. Mercury, oddly, looks like a comet as it is sporting a long
    ion tail made of sodium. The image was acquired last week. Please see
               the explanation for more detailed information.

                            Mercury's Sodium Tail
               Image Credit & Copyright: [3]Sebastian Voltmer

   Explanation: That's no comet. Below the [4]Pleiades star cluster is
   actually a planet: Mercury. Long exposures of our [5]Solar System's
   innermost planet may reveal something unexpected: a tail. [6]Mercury's
   thin [7]atmosphere contains small amounts of [8]sodium that glow when
   excited by light from the Sun. Sunlight also liberates these molecules
   from [9]Mercury's surface and pushes them away. The yellow glow from
   [10]sodium, in particular, is relatively bright. Pictured, Mercury and
   its [11]sodium tail are visible in a deep image taken last week from
   [12]La Palma, [13]Spain through a filter that primarily transmits
   [14]yellow light emitted by sodium. First [15]predicted in the 1980s,
   Mercury's tail was first [16]discovered in 2001. Many tail details were
   revealed in [17]multiple observations by [18]NASA's robotic
   [19]MESSENGER spacecraft that orbited Mercury between 2011 and 2015.
   [20]Tails, of course, are usually associated with [21]comets.

                  Tomorrow's picture: planet pyramid parade
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    Authors & editors: [33]Robert Nemiroff ([34]MTU) & [35]Jerry Bonnell
                                 ([36]UMCP)
          NASA Official: Phillip Newman [37]Specific rights apply.
              [38]NASA Web Privacy Policy and Important Notices
                A service of: [39]ASD at [40]NASA / [41]GSFC
                           & [42]Michigan Tech. U.

References

   1. https://apod.nasa.gov/apod/archivepix.html
   2. https://apod.nasa.gov/apod/image/2205/MercuryTailPleiades_Voltmer_1448.jpg
   3. https://www.voltmer.de/about/
   4. https://apod.nasa.gov/apod/ap211124.html
   5. https://solarsystem.nasa.gov/planets/mercury/overview/
   6. https://apod.nasa.gov/apod/ap170723.html
   7. https://en.wikipedia.org/wiki/Atmosphere_of_Mercury
   8. https://en.wikipedia.org/wiki/Sodium
   9. https://apod.nasa.gov/apod/ap110616.html
  10. https://youtu.be/dmcfsEEogxs?t=49
  11. https://www.psi.edu/news/cover-pages/2018/mercurys-sodium-tail
  12. https://youtu.be/Ub9622tvuUM?t=12
  13. https://en.wikipedia.org/wiki/Spain
  14. https://www.youtube.com/watch?v=7u3rRy97m9Y
  15. https://ui.adsabs.harvard.edu/abs/1986GeoRL..13..423I/abstract
  16. https://ui.adsabs.harvard.edu/abs/2001mses.conf...77P/abstract
  17. https://www.nasa.gov/image-feature/mercurys-sodium-tail
  18. https://www.nasa.gov/
  19. https://www.nasa.gov/mission_pages/messenger/main/index.html
  20. https://i.pinimg.com/originals/04/16/2e/04162ebbb47b9421cfceedf0908482d2.jpg
  21. https://apod.nasa.gov/apod/ap220112.html
  22. https://apod.nasa.gov/apod/ap220502.html
  23. https://apod.nasa.gov/apod/archivepix.html
  24. https://apod.nasa.gov/apod/lib/apsubmit2015.html
  25. https://apod.nasa.gov/apod/lib/aptree.html
  26. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  27. https://apod.nasa.gov/apod/calendar/allyears.html
  28. https://apod.nasa.gov/apod.rss
  29. https://apod.nasa.gov/apod/lib/edlinks.html
  30. https://apod.nasa.gov/apod/lib/about_apod.html
  31. http://asterisk.apod.com/discuss_apod.php?date=220503
  32. https://apod.nasa.gov/apod/ap220504.html
  33. http://www.phy.mtu.edu/faculty/Nemiroff.html
  34. http://www.phy.mtu.edu/
  35. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  36. http://www.astro.umd.edu/
  37. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
  38. https://www.nasa.gov/about/highlights/HP_Privacy.html
  39. https://astrophysics.gsfc.nasa.gov/
  40. https://www.nasa.gov/
  41. https://www.nasa.gov/centers/goddard/
  42. http://www.mtu.edu/