Did you know that...
Nights are shorter than days on average due to two factors. Firstly,
the sun is not a point, but has an apparent size of about 32
arc minutes. Secondly, the atmosphere
refracts
sunlight so that some of it reaches the ground when the sun is below
the horizon by about 34 arc minutes. The combination of these two
factors means that light reaches the ground when the center of the sun
is below the horizon by about 50 arc minutes. Without these effects, day
and night would be the same length at the
autumnal (autumn/fall) and
vernal (spring)
equinoxes, the moments when the sun passes over the
equator. In reality, around the equinoxes the day is almost 14 minutes longer than the night at the equator, and even more towards the
poles. The summer and winter
solstices mark the shortest and the longest night, respectively. The closer a location is to either the
North Pole or the
South Pole,
the larger the range of variation in the night's length. Although
equinoxes occur with a day and night close to equal length, before and
after an equinox the ratio of night to day changes more rapidly in
high latitude locations than in
low latitude locations. In the
Northern Hemisphere,
Denmark has shorter nights in June than
India has. In the
Southern Hemisphere,
Antarctica has longer nights in June than
Chile
has. The Northern and Southern Hemispheres of the world experience the
same patterns of night length at the same latitudes, but the cycles are 6
months apart so that one hemisphere experiences long nights (winter)
while the other is experiencing short nights (summer).
Between the pole and the polar circle, the variation in daylight
hours is so extreme that for a portion of the summer, there is no longer
an intervening night between consecutive days and in the winter there
is a period that there is no intervening day between consecutive nights.
http://en.wikipedia.org/wiki/Night
