                        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.

                              2023 September 23

                             Afternoon Analemma
            Image Credit & Copyright: Ian Griffin (Otago Museum)

   Explanation: An analemma is that figure-8 curve you get when you mark
   the position of the Sun at the same time each day for one year. To make
   this one, a 4x5 pinhole camera was set up looking north in southern New
   Zealand skies. The shutter was briefly opened each clear day in the
   afternoon at 4pm local time exposing the same photosensitized glass
   plate for the year spanning September 23, 2022 to September 19, 2023.
   On two days, the winter and summer solstices, the shutter was opened
   again 15 minutes after the main exposure and remained open until sunset
   to create the sun trails at the bottom and top of the curve. The
   equinox dates correspond to positions in the middle of the curve, not
   the crossover point. Of course, the curve itself is inverted compared
   to an analemma traced from the northern hemisphere. And while fall
   begins today at the Autumnal Equinox for the northern hemisphere, it's
   the Spring Equinox in the south.

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