                        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 October 21

                                Quarter Moons
               Image Credit & Copyright: Marcella Giulia Pace

   Explanation: Half way between New Moon and Full Moon is the Moon's
   first quarter phase. That's a quarter of the way around its moonthly
   orbit. At the first quarter phase, half the Moon's visible side is
   illuminated by sunlight. For the Moon's third quarter phase, half way
   between Full Moon and New Moon, sunlight illuminates the other half of
   the visible lunar disk. At both first and third quarter phases, the
   terminator, or shadow line separating the lunar night and day, runs
   down the middle. Near the terminator, long shadows bring lunar craters
   and mountains in to sharp relief, making the quarter phases a good time
   to observe the Moon. But in case you missed some, all the quarter
   phases of the Moon and their calendar dates during 2022 can be found in
   this well-planned array of telephoto images. Of course, you can observe
   a first quarter Moon tonight.

                    International: Observe the Moon Night
                 Tomorrow's picture: ghostly northern lights
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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