My 2-month-old daughter consistently fusses or screams around sundown/nightfall regardless of the sky being overcast, the lights in the house being on, or apparently any other factor.
Is this common, and is there any known reason it happens?
See http://www.purplecrying.info. In short, it's a phase all children go through, some more severely than others, but the crying is a natural part of a baby's development. It helps baby's lungs develop, helps the baby bond with its parents (or whomever shows up when the crying starts), and in trying to soothe your baby you'll introduce visual, aural and tactile stimulation that helps your baby's brain develop.