How do streetlights make it harder for us to see the stars in the night sky?
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Light is a stream of weird things called photons that we can just imagine as tiny balls for this answer. Your eye has a bunch of “buckets” inside of it, and the eye sort of works by counting how many balls hit each “bucket” in an instant.
A dim light doesn’t shoot very many balls at your eye. A bright light shoots a lot more. If you think this through, you can see how bright lights hide dim lights.
So when you’re looking at a star, your eye is noticing that some small cluster of “buckets” is getting hit by a few photons and you see a dim small light corresponding to that. A streetlamp blasts millions of photons in every direction. Now your eye sees that all of your “buckets” have a small amount of balls in them. The parts where the star should be have a few more balls inside, but your eye isn’t very good at telling the difference between 3,000 photons and 3,010 photons, so you can’t really see the star anymore.
The stars you can still see under streetlamps are the ones bright enough to emit so many photons your eye can still tell that part of the sky is brighter than others.
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