This column is provided as a public service by the Geophysical Institute, University of Alaska Fairbanks, in cooperation with the UAF research community. T. Neil Davis is a seismologist at the institute. Were it not for refraction of the sun's rays in the atmosphere, the shortest day would equal the shortest night at a particular latitude.
Atmospheric refraction bends the rays so that they can pass over the horizon.
Hence, the sun appears to rise before it actually reaches the horizon and it is still visible at night after it is actually below the horizon. Consequently, every day is longer than it would be if there were no refraction.