                        Astronomy Picture of the Day

    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.

                              2021 November 30

                         In Motion: Uranus and Moons
        Video Credit: David Campbell (U. Hertfordshire), Bayfordbury
                                 Observatory

   Explanation: What's that moving across the sky? A planet just a bit too
   faint to see with the unaided eye: Uranus. The gas giant out past
   Saturn was tracked earlier this month near opposition -- when it was
   closest to Earth and at its brightest. The featured video captured by
   the Bayfordbury Observatory in Hertfordshire, UK is a four-hour
   time-lapse showing Uranus with its four largest moons in tow: Titania,
   Oberon, Umbriel and Ariel. Uranus' apparent motion past background
   stars is really dominated by Earth's own orbital motion around our Sun.
   The cross seen centered on Uranus is called a diffraction spike and is
   caused by light diffracting around the four arms that hold one of the
   telescope's mirrors in place. The rotation of the diffraction spikes is
   not caused by the rotation of Uranus but, essentially, by the rotation
   of the Earth. During the next few months Uranus itself will be visible
   with binoculars, but, as always, to see its moons will require a
   telescope.

                   Tomorrow's picture: the blood moon band
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
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