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posted 5mo ago by Olin Lathrop‭

The light shines on everything in an unblocked direct line from the light source.  This light is quite bright, so can be seen by human eyes all the way out to the horizon (until the curvature of the earth ends up blocking the direct line).
Now consider the reverse.  The sun makes plenty of light to read a newspaper by.  But as a result, it is too bright to look at directly without damaging your eyes.  That same ratio of direct-sun brightness to newspaper brightness applies to all other light sources too, like a lighthouse 5 miles away, or a star 50 light years away.