What are the Northern lights? (Aurora Borealis)

Northern Lights in Rovaniemi, Lapland - www.lifeinlapland.com
In December of 2013, a solar maximum occured, which is the most active period of the current solar cycle. As a result of this maximum, the Northern Lights will be more visible in Lapland over the next few Winters than compared to other years in the past. Already in August and September, the sky has lit up with dancing auroras which could be seen from all different areas of Lapland and the far North. The first northern lights show was seen over Rovaniemi already on the in August 2015.

But ever wondered what exactly are the northern lights? Where do they appear from? Well, here's a bit of an overview.

The phenomenon of the Northern Lights is caused by the stress of solar wind on the earth's magnetic field, which protects the earth from external electromagnetic interference. The field is at its weakest closer to the north and south poles, so the auroras can be seen either in the Nordic countries (Aurora Borealis - Northern Lights), or in the southern hemisphere (Aurora Australis).
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When the solar wind reaches the Earth, it activates electrons of oxygen and nitrogen which, when having excess energy, give off light that is visible to from earths surface (where we live!). All of this action takes place between a height of 90 to several hundred kilometers above the earth's surface.
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Oxygen gives off a green light at altitudes of between 70-150 km and reddish light at an altitude of 150-400 km, as the fading glow of the higher lights is slower. Nitrogen, when activated, gives either or purple or green light (like in the picture below).
Lapland Auroras - www.lifeinlapland.com
The Northern Lights can be seen for hundreds of miles farther south than from where they are actually occurring overhead, thats why sometimes they are visible close to the horizon only, and sometimes visible right above you. An example of their visual reach can be observed by the red border in the image below. You can follow the position of the red line on this website.
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Solar activity is subject to an eleven-year cycle which can be traced with the help of sunspots. During a solar minimum, sunspots on the sun are not quite formed and much less than during a maximum. For example, 2008 had the lowest periods of solar activity in the last century, which you can see in the chart below (number of sun spots observed per year since 1880).
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The activity levels of the current solar cycle are much lower than predicted by scientific sources, and apparently, it will be the calmest cycle of the last 100 years. However, scientists at NASA are still waiting for the effect of a double peak, and that is to propose that the second half of the activity is still to come (see chart below).
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The best time to observe the northern lights in the autumn and the spring equinox, that is, in August-October and February-April. At these moments, the magnetic field of the earth is most vulnerable, so even a slight increase in solar activity can cause a visible glow above the horizon.

If visiting Lapland and staying for a few days in Autumn, Winter, or early Spring, you may have a chance to experience the unique sight of dancing lights across the northern sky. You can read more here about how to predict aurora forecasts if you're up for the challenge of hunting for the lights on your own.
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