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 January 2

                       21st Century Wet Collodion Moon
                  Image Credit & Copyright: Mike Smolinsky

   Explanation: In the mid 19th century, one of the first photographic
   technologies used to record the lunar surface was the wet-plate
   collodion process, notably employed by British astronomer Warren De la
   Rue. To capture an image, a thick, transparent mixture was used to coat
   a glass plate, sensitized with silver nitrate, exposed at the
   telescope, and then developed to create a negative image on the plate.
   To maintain photographic sensitivity, the entire process, from coating
   to exposure to developing, had to be completed before the plate dried,
   in a span of about 10 to 15 minutes. This modern version of a wet-plate
   collodion image celebrates lunar photography's early days, reproducing
   the process using modern chemicals to coat a glass plate from a 21st
   century hardware store. Captured last November 28 with an 8x10 view
   camera and backyard telescope, it faithfully records large craters,
   bright rays, and dark, smooth mare of the waxing gibbous Moon.
   Subsequently digitized, the image on the plate was 8.5 centimeters in
   diameter and exposed while tracking for 2 minutes. The wet plate's
   effective photographic sensitivity was about ISO 1. In your smart
   phone, the camera sensor probably has a photographic sensitivity range
   of ISO 100 to 6400 (and needs to be kept dry ...).

                     Tomorrow's picture: northern lights
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
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