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in June is most often the longest day. Greenland has chosen this date as its national day, and Ullortuneq
which is the Greenlandic name for this day, translates into that which is richest in daytime .
However, in some years the longest day is June 20 or rarely June 22. This is due to the fact that a calendar
year is not exactly 8760 hours (i.e. 365 x 24 hours), but 8765 hours 58 minutes 45 seconds. Every
year the solstice will be moved forward almost 6 hours until a leap year moves it back 24 hours by adding
an extra day, February 29 that is. In 2005 West Greenland had summer solstice at June 20 at 21:57 and
again in 2008 the longest day will be June 20. We have to wait until 2104 to see a summer solstice at June
22.
It does not make sense to talk about day length in regions where the sun is above the horizon all 24 hours,
because it is day all the time. From the Arctic Circle and northwards the sun is above the horizon day and
night at summer solstice. If one looks at a low angle over the horizon, the refraction of light makes it possible
to actually see the midnight sun even though one is as far south as 65°45 N (i.e. 89 km south of the Arctic
Circle), but one must have an unobstructed northwards view over the sea.
Between sunset and sunrise there are crepuscular periods of varying length. When the sun is less than 6°
below the horizon, it is known as civil twilight (in old days the civic population should hurry home before it
Danish Polar Center
IPY Service Manual for Kangerlussuaq 2008
version 1 June 2008
Compiled and written by Henning Thing (het@fi.dk)
Danish Polar Center Danish Agency for Science, Technology and Innovation
page 52 of 60
was needed to light the lamps). When the sun is between 6° and 12° below the horizon the twilight is called
nautical (sailors would have light enough to see the horizon and darkness enough to spot the brightest
stars). The deepest twilight rules when the sun is 12-18° below the horizon; then it is astronomical twilight
(most individual stars can be spotted clearly but not yet the Milky Way).
The part of the summer that we call the light nights is the period when the sun sinks to less than 18° below
the horizon. The southern tip of Greenland does not experience any midnight sun but the light nights
range from April 22 and until August 19. At the northernmost point of Greenland light nights start February
19, are followed by the 24-hour-sun April 4 through September 9, and resume until October 23 when at that
time the polar night rules once again. Therefore, at Oodaap Qeqertaa, Oodaaq Island, the longest day is
actually 22 weeks long ! - Only 5 weeks shorter that at the North Pole.
[Kangerlussuaq: Continuous daytime for 6 weeks]
The mobile blood bank
A summer in Greenland will provide you with really good opportunities for you to experience the unpleasant
with black feet also known as Aëdes nigripes also known as the mosquito, the most common animal in
Greenland. Before you swat the creature while it s trying to do its job one ought to take a closer look at this
infamous but most interesting insect.
The mosquito lives of plant juice and flower nectar and the sugar in this is used as fuel during flight. Only
the females can bite and suck blood; if a female can not locate a blood donor she will produce only 5-7
eggs but if she gets the chance to eat a protein-rich blood meal on a bird or a mammal, she can produce
several hundreds of eggs.
The male mosquito is equipped with two hairy and sound sensitive antenna that are finely tuned to detect
and receive the frequency 380 Hz which corresponds to the wing beat frequency of the female mosquito.
Using his two antennae the male homes in on a flying female and immediately upon touch down the pair
mates; this happens most often 1-2 days after the mosquitoes have emerged from the pupae. In turn, the
female mosquito is tuned in on the frequency of the male wings: 230 Hz.
To find and approach a victim the female mosquito uses the CO2 in the exhaled air and the body odours of
the potential blood donor. A sweaty and warm human face is a magnificent mosquito magnet. The female
also is stocked with a heat sensor which can detect fractions of a °C. Therefore, once landed on a donor,
the female will always have the best chances of finding a spot on the skin under which a blood vessel is
within reach.
Ready to penetrate, the female unsheathes her complicated proboscis and proceed to saw through the
skin using two pairs of sharp ultra-thin and serrated blades that work almost like the ones in an electric
hedge cutter. Through one of two tubes she drips a chemical into the wound that keeps the blood from clotting
and the blood vessel from contracting. Through the other tube blood is sucked up into the mosquito.
　
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