Auroras are natural light displays in the sky, usually seen at night, and particular to the polar regions. They occur in the ionosphere, and are called polar auroras. They are most commonly visible between 65 and 72 degrees north and south latitudes, which would place it in a ring just inside the Arctic and Antarctic Circles. In the north, it is known as the Aurora Borealis, named after the Roman goddess of dawn, Aurora, and the Greek name for the north wind, Boreas, so named by Pierre Gassendi in 1621.
The Aurora Borealis is also known as the northern lights, and is visible in the sky only from the Northern Hemisphere. The southern counterpart, the aurora australis, is visible only from high southern latitudes in Antarctica, South America, and Australia. And Auroras can be observed from other locations on earth, but best view closer to the poles due to the longer periods of darkness and the magnetic field.
What is the mechanism of the Auroras? Auroras are the result of emission of photons in the Earth’s upper atmosphere (above 50 miles). The photons come from ionized nitrogen atoms regaining an electron, and oxygen and nitrogen atoms returning from an excited state to a ground state. The ionization is caused by solar wind particles funneled and accelerated along the Earth’s magnetic field lines. Oxygen emissions are green or brownish red, while nitrogen emissions are red or blue.
Most of the time, the Auroras appear as a diffuse glow or a moving “curtains” that extend in an east west direction. Arcs can also form due to constant changes, shaped by the Earth’s magnetic field. The greatest geomagnetic storm occurred in 1859. The best time to watch the Northern Lights is December to March, when the nights are longest and the sky is darkest. The aurora may only last for 10 to 15 minutes. Ours lasted over an hour!
The aurora is most active late at night or early in the morning, when the sky is clear and the air chilly. The best time to watch is in spring and fall, especially February, March, September, and October. One of the best times to look for the Northern Lights will be when it is dark because of a new moon.
(from the Finnish Meteorological Institute)
The occurrence of auroras depends on the latitude of the observer. The Northern Lights form an oval band around the magnetic poles of the Earth. At a distance about 2500 km from these poles, the probability for seeing auroras is almost 100 %.
The northern parts of Fennoscandia belongs to the maximum auroral zone. In the coast of Ice Sea in North-Norway you will see auroras almost every evening when the sky is clear enough. When moving southwards, the frequency of auroras decreases. In Sodankylä every second night is an auroral night, in Helsinki every 20th. These are statistical rules giving the average extent of auroras. When the Earth’s magnetic field is very disturbed, the auroras can spread all over Europe for a couple of hours.
The best time to see auroras is between 9 p.m. – 3 a.m. local time. The best months are February – March and September – October. During summer months you cannot see aurora due to light nights. April was just fine!!!
This was the first of two trips to see the Aurora. Wish me clear viewing, if I can stay awake until 5am this morning! I must say it filled the sky, and created much excitement among my fellow viewers.