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Home , Daytime, Midnight sun

NORDIC LIGHT & COLOUR

The highest elevation angle of the during the shortest sun does not occur in the capitals of Nordic countries of the year, 21st of December, is only 3,35°. In the period from and other settled areas situated about 60° N. the 21st of December to the beginning of February the elevation angle of the sun will never reach 10°, this occurs first on the Duration of sunny 3rd of February. After this day the number of when the We should not forget that availability of is also strongly sun is over 10° increases rapidly on a daily basis, but we have dependent on the cloud cover. Let us look at the frequency of to wait until the 30th of March to observe the sun reaching the sunny skies. For this purpose four maps were generated with 30° elevation angle. the help of the Satel-Light (Satel-Light 2013), see figure 8 and The highest position of the sun in Trondheim is 50,01°. There 9. are only four days during the year, 19th, 20th, 21st and 22nd of June, when the elevation angle of the sun is higher than 50°; at The frequency of “sunny skies” during the year in Europe 21st of June it lasts for 12 minutes. of the Alps is rather low (30-40%), the British Islands receive the least sunlight. In the Nordic region covered by the satel- lite and shown on the map, the highest frequencies of sunny skies may be found at the Baltic See (40-45%), the lowest in the Norwegian mountains (20-25%), see figure 8. A large differ- ence may be observed between different and different months of the year. Generally, the highest frequency of sunny skies occurs in the , the lowest in the , figure 9.

Special features of in Nordic region The analysis made so far shows the typical features of daylight Table 2. The time duration in hours when the sun is in the three elevation angle intervals, calculated monthly for the first part of the year in Trond- in the Nordic countries: heim. 1. Dominating low solar elevation angle during the year 2. Long periods of and white in the time period close to , at places north of the The results are striking: the percentage of time when the sun is Circle between 0° and 10° is 35%. This means that for more than 1/3 3. Rather low frequency of sunny skies during the year, espe- of the whole during the year we may expect a nearly cially during winter horizontal light from the sun. The time when the sun is in the 0°-10° angle interval is actually much longer than the time What are the consequences of the dominating low solar eleva- when it is over 30° (26%). tion and low occurrence of sunny skies?

Twilight When solar elevation angle is low, the sunlight accessibility is Since the sun stays for that long time just over the , it obviously low as well, in buildings and outside, especially in may also stay for a long time just beneath the horizon. To ex- mountain regions and areas with undulating terrain. amine this, the twilight time was calculated! The twilight is de- Even if the sunlight is present, it has much lower luminous flux fined as a condition where the sun is no more than 6° beneath than in southernmost regions, it is not perceived as dangerous- the horizon. The total twilight duration, 430 h for ½ year, i.e. 860 ly strong, both for the people and for the natural environment. h a year, is a long time. Twilight makes 19% of the -time The modelling of terrain and objects is sparse and gentle. during the year (the length of the daytime and the night-time The low position of the sun contributes to frequent occurrence in a year is equal). The twilight duration is longest during the of solar glare, i.e. an experience of the presence of the sun in summer months. During the four weeks period closest to the the visual field of a subject. (21st of June) the twilight is strong enough to The low sun is even more annoying than a high sun, since the illuminate landscape and people quite well, even daytime ac- direction of view is very often horizontal, at least outdoors. tivities, such as reading, are still possible without artificial light People living in Nordic region are annoyed by solar glare quite on a clear night. There is no really dark time during the whole often; they have worked out an intuitive, unconscious method night; the white night is a fact. for dealing with the solar glare, e.g. by turning the body and/or White nights should not be mixed up with midnight sun that oc- visual object to a more comfortable position. Also simple sun curs only at places north of the 66° 33’ 44’’N. The shading methods have been developed for usage in buildings,

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