Why are the first hour or two after sunset less productive for stargazing than later hours?
Answer
The sky is still too bright before astronomical twilight ends
The sky does not achieve instantaneous perfect darkness once the sun drops below the horizon. Stargazing productivity is directly related to the level of ambient light present. Since the sky remains illuminated due to the scattering of sunlight during civil and nautical twilight phases, the sky is technically still too bright for optimal viewing during the first hour or two post-sunset. Critical observation—the arrival of true darkness—only begins after the astronomical twilight phase concludes, which occurs when the Sun is located more than 18 degrees below the horizon.
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