Autor: Tau'olonga
Fecha: julio 2006
Licencia: Creative Commons. Puede copiarse, debe mencionarse al autor
Descripción: Arco diurno del Sol, cada hora en los 2 solsticios, vistos en el cielo desde una latitud de 50 grados. También se muestran "soles crepusculares" hasta los -18º de elevación.

"The day arcs at 50° latitude. The winter Sun does not rise more than 16.56° above the horizon at midday, and 63.44° in summer above the same horizon direction. The difference in the length of the day between summer and winter is striking - slightly less that 8 hours at midwinter, to slightly more than 16 hours in midsummer. Likewise is the difference in direction of sunrise and sunset. Also note the different steepness of the daily path of the Sun above the horizon in summer and winter. It is much shallower in winter. Therefore not only is the Sun not reaching as high, it also seems not to be in a hurry to do so. But conversely this means that in summer the Sun is not in a hurry to dip deeply below the horizon at night. At this latitude at midnight the summer sun is only 16.56° below the horizon, which means that astronomical twilight continues the whole night. This phenomenon is known as the grey nights, nights when it does not get dark enough for astronomers to do their observations. Above 60° latitude the Sun would be even closer to the horizon, only 6.56° away from it. Then civil twilight continues the whole night. This phenomenon is known as the white nights. And above 66° latitude, of course, one would get the midnight sun."