How do streetlights make it harder for us to see the stars in the night sky?
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Most of the issue is with dark adaptation in your eyes. Your pupils can dilate (grow large to let in more light) in just a few seconds but your eyes also have a chemical adaptation process that can take over 20 minutes to complete. Then they’re much more sensitive and you can see more things in the dark, including dimmer stars.
Just a quick glance at a bright object will ruin this “night vision” meaning you have to wait the 20 minutes all over again. Amateur astronomers use dim red torches (flashlights) to do things like read charts and adjust telescopes because this can avoid losing night vision. Street lights near an observing site are a disaster unless you’re viewing bright objects like the moon and planets.
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