Long-exposure color photographs of the night sky often show regions that glow red,such as the Rosette Nebula in Figure 11-6 of Comins,Discovering the Essential Universe,6th ed.This distinctive red color is caused by the:

Question

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The distinctive red color in long-exposure color photographs of the night sky is caused by the ionization and subsequent recombination of hydrogen atoms in the Rosette Nebula. This process emits red light, which can be captured in the photograph.

Long-Exposure Color Photographs of the Night Sky Often Show Regions