                        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.

                                2026 June 21
   An image of the sky over the Netherlands taken every 15 seconds during
   2025. Visible are night, day, solstices, equinoxes, moonglow, the blue
        hour, and more. Please see the explanation for more detailed
                                information.

                          Keogram: The Sky in 2025
     Image Credit & License: Cees Bassa (Netherlands Institute for Radio
                                 Astronomy)

   Explanation: What if you could see the entire sky -- all at once -- for
   an entire year? That, very nearly, is what is pictured here. Every 15
   seconds during 2025, an all-sky camera took an image of the sky over
   the Netherlands. Central columns from these images were then aligned
   and combined to create the featured keogram, with January at the top,
   December at the bottom, and the middle of the night running vertically
   just left of center. What do we see? Most obviously, the daytime sky is
   mostly blue, while the nighttime sky is mostly black. The twelve light
   bands crossing the night sky are caused by the glow of the Moon. The
   thinnest part of the black hourglass shape occurs during the summer
   solstice, like today, when days are the longest, while the thickest
   part occurs at the winter solstice. Equinoxes can also be located in
   the keogram, for example the northern-spring equinox from one year ago
   is about three-quarters of the way up.

                      Tomorrow's picture: Sun's future
     __________________________________________________________________

       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Amber Straughn Specific rights apply.
                  NASA Web Privacy, Accessibility, Notices;
                      A service of: ASD at NASA / GSFC,
                           NASA Science Activation
                             & Michigan Tech. U.

