Does sunset occur when the sun first touches the horizon or when it dips below it?
Dear Tom,
Does sunset occur when the sun first touches the horizon or when it dips below it?
Dan Stecich Orland Park
Dear Dan,
Sunset and sunrise are defined as the moment that the upper edge of the sun's disc
touches the horizon. At the exact time of sunrise or sunset the sun's disc is actually
below the horizon, but because the Earth's atmosphere bends or refracts light, we are
able to see the sun earlier in the morning and later in the evening than if we were
viewing it in a vacuum. Since the higher we are, the farther we can see, a person atop a
high-rise building or on a mountain will actually experience an earlier sunrise and a
later sunset than someone at ground level. Also the few extra minutes that we are able
to see the sun is the reason that the length of daylight on the equinoxes or at the
equator is slightly greater than 12 hours.