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As the Earth travels
around the Sun in its orbit, the north-south
position of the Sun changes over the course of
the year due to the changing orientation of the
Earth's tilted rotation axes. The dates of
maximum tilt of the Earth's equator correspond
to the
Summer Solstice and
Winter
Solstice, and the dates of zero tilt to the
Spring or
Vernal Equinox and
Autumnal Equinox.
The first day of
winter (the
winter solstice) is
the shortest day of the
year and the first day
of summer (the
summer solstice) is
the longest day of the
year. In the
United States, there are
only about 9½ hours of
daylight on the first
day of winter and about
14½ hours of daylight on
the first day of summer.
During the summer
months, the further
north you go, the arc of
solar travel between
sunrise and sunset
lengthens and the amount
of daylight increases.
For regions north of the
Arctic Circle (at a
latitude of 66.5
degrees), there will be
at least one 24-hour day
during which the sun
will not set as the
solar arc lengthens to a
complete circle.
It will approach the
horizon at midnight, but
it will not quite touch
it and the Sun will
shine all day long.
At the latitude of the
Arctic Circle, the first
day of summer is the
only 24-hour day of
total daylight.
Further north toward the
Pole, the number of
24-hour periods between
sunrise and sunset
increases. The
ultimate long-day occurs
at the North Pole where
the Sun rises with the
Vernal Equinox and
finally sets again 189
days later with the
Autumnal Equinox.
Likewise, during the winter months, for
regions north of the Arctic Circle, the sun will
set for for at least one full day before rising
again. Further north toward the Pole, the
number of 24-hour periods before the sun rises
again increases. At the North Pole, the
sun will not rise again until the Vernal
Equinox.
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