Which lines decide duration of day and night?

Answer 1

Every point along the same line of latitude has the same amount of time between sunrise and sunset at any given moment. That amount of time grows gradually shorter from the time of the summer solstice until the time of the winter solstice, and it grows gradually longer from the winter solstice until the summer solstice. Also, higher altitudes at the same latitude and longitude will see the sun slightly longer.