Northern Lights (Auroras)
The sun emits electrically charged particles, protons, electrons, and ions, towards the Earth. The Earth's magnetic field deflects these particles, and they collide with the Earth's atmosphere in regions around the 70th latitude. The particles are ejected from the sun at speeds ranging from 300 to 800 km/s. The distance from the sun to Earth is about 150 million kilometers, which the particles cover in 2-6 days. Light, on the other hand, only takes 8 minutes for this distance! There are two annular regions on Earth around the two magnetic poles where the electric particles meet or collide with the components of the Earth's atmosphere. However, the magnetic poles are not identical to the geographic poles. The magnetic poles are located in northern Canada and in the Arctic south of Australia. The annular regions are centered around these two areas and not around the geographic poles.
During the collision of solar particles with Earth's atmospheric particles, electrons of oxygen and nitrogen atoms are raised to a higher energy level. When the electron falls back to its normal state, photons with energy equivalent to the energy difference of the electron are emitted. Depending on the energy difference, red light (oxygen at 630 nm), green light (oxygen at 557 nm), or blue and violet light (nitrogen) is created, which can be observed on the Earth's surface. So, what we see is not the solar wind particles directly but the light generated after the collision. The lights are created at high altitudes: red light above 200 km, green light between 120 and 140 km.
Depending on the strength of the solar wind and how much the Earth's magnetic field is deformed by the solar wind, you can also see auroras in more southerly regions. The lights are generated throughout the day but are only visible in the evening or at night, as they would otherwise be overwhelmed by sunlight. There is a good chance of observing auroras during a visit to Lapland. However, weather conditions can affect the viewing experience. In the north, the aurora is called Aurora Borealis or Northern Lights, while in the south, it is called Aurora Australis or Southern Lights.
Information on photographing auroras is described in the articles Photographing Auroras and Experiences with Auroras 2008.
The following galleries were captured during various visits to Finnish Lapland.
Auroras I
Auroras II
Auroras III
Aurora in Southern Sweden
