retrofutureground:Edward Emerson Barnard, Mars, photographed with the Yerkes Observatory 40-inch ref
retrofutureground:Edward Emerson Barnard, Mars, photographed with the Yerkes Observatory 40-inch refractor telescope, 29-09-1909. Above: Syrtis Major region, September 29, 3: 45 (UT); Below: Same; 4: 25 (UT). Each exposure is the superposition of three to five original frames. This reduces grain and brings out fine halftones. -- source link
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