                        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.

                              2022 September 18

                     Analemma over the Callanish Stones
                 Image Credit & Copyright: Giuseppe Petricca

   Explanation: If you went outside at the same time every day and took a
   picture that included the Sun, how would the Sun's position change? A
   more visual answer to that question is an analemma, a composite image
   taken from the same spot at the same time over the course of a year.
   The featured analemma was composed from images taken every few days at
   noon near the village of Callanish in the Outer Hebrides in Scotland,
   UK. In the foreground are the Callanish Stones, a stone circle built
   around 2700 BC during humanity's Bronze Age. It is not known if the
   placement of the Callanish Stones has or had astronomical significance.
   The ultimate causes for the figure-8 shape of this and all analemmas
   are the tilt of the Earth axis and the ellipticity of the Earth's orbit
   around the Sun. At the solstices, the Sun will appear at the top or
   bottom of an analemma. The featured image was taken near the December
   solstice and so the Sun appears near the bottom. Equinoxes, however,
   correspond to analemma middle points -- not the intersection point.
   This coming Friday at 1:04 am (UT) -- Thursday in the Americas -- is
   the equinox ("equal night"), when day and night are equal over all of
   planet Earth. Many cultures celebrate a change of season at an equinox.

                Explore Your Universe: Random APOD Generator
                     Tomorrow's picture: lightning layer
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