Aurora Borealis
The aurorae appear over the Earth’s polar regions in what are known as the auroral ovals; in the northern hemisphere the auroral oval bulges that much further to the south, the stronger the solar wind is at any given moment. The oval normally extends over northern Finland and Scandinavia, the whole of Canada and the northern USA, Alaska and Siberia. In the event of a solar storm, it may reach as far south as the skies over central Europe. Because the oval does not extend symmetrically around the Earth's rotational axis, each degree of the Earth’s longitude rotates deeper into the oval once every 24 hours; in the case of Finland this rotation means the best time for viewing the Northern Lights is around 10.30 in the evening (Standard Time). On the other hand, it is always worth bearing in mind that a solar storm can appear at any time of the day or night, and hunters of spectacular shows would therefore be well advised to concentrate on following the various types of forecasts and predictions which are published on the Internet. (Virtual Finland, 2001)
Auroras are visible in northern Finland from beginning of September to middle of April. Auroras occur also during summertime, but the night are too light during that period and you cannot see auroras at all. In normal case auroras occur in Finland sector between 21 - 01 in evening, with the maximum around 22 - 23. However, during geomagnetically active times (read: lots of variations and disturbances in near-Earth space which also cause auroras) auroras can be visible during the whole night from 18 - 06.
Certain cycles can be found from auroral activity. Most important of these are 11-year cycle, 27 day cycle and annual variations. Suns activity, which is also the main reason of auroras, varies in 11-year cycle. Activity deceases from maximum to minimum in roughly 6 year, and returns to maximum in 5 years. During the maximums auroras are more probable, and during the minimums auroras occur less. This effect especially lot to big auroral storms, when auroras can be seen far south; these are much more probable during suns activity maximum. Currently (November 2000) we are living in middle on maximum time. The 27 day cycle is caused by Suns rotation. Equatorial region of the Sun rotates around once in 27 days, so if some specific region causes strong auroras, it is possible that it causes auroras again after 27 days. An annual variation can also be found. Auroras are more probable during autumn and spring equinoxes than during winter solstice. So in that sense, October and March might be good months to go to north (Jussila, 2001).
The probability to see auroras is highest in Kilpisjärvi, the northern most top in the "hand" of Finland, 75 %. Probability decreases so that in Rovaniemi area probability is roughly 45 %, in Oulu area about 30 %, in Tampere 10 % and in Helsinki area only 5 %. (Jussila, 2001). At Häme Polytechnic Mustiala a perfect Aurora borealis with the centre in the middle, in full colours was seen about 22.00 in the evening in March 1999, more than 10 foreign exchange students saw it. Aurora borealis could be seen in the end of October 2001 in southern Finland.
Look at the amazing phenomen of Aurora Borealis on photos taken by Jouni Jussila