What is the Aurora Borealis?

WHAT IS THE AURORA BOREALIS?

Aurora Oval

The Aurora is an incredible light show caused by collisions between electrically charged particles released from the sun that enter the earth’s atmosphere and collide with gases such as oxygen and nitrogen. The lights are seen around the magnetic poles of the northern and southern hemispheres.

Auroras that occur in the northern hemisphere are called ‘Aurora Borealis’ or ‘northern lights’ and auroras that occur in the southern hempishere are called ‘Aurora Australis’ or ‘southern lights’.

Both Aurora’s can be seen in the northern or southern hemisphere, in an irregularly shaped oval centred over each magnetic pole. Scientists have learned that in most instances northern and southern auroras are mirror-like images that occur at the same time, with similar shapes and colours. Auroral displays can appear in many vivid colours, although green is the most common. Colours such as red, yellow, green, blue and violet are also seen occasionally. The auroras can appear in many forms, from small patches of light that appear out of nowhere to streamers, arcs, rippling curtains or shooting rays that light up the sky with an incredible glow.

 

WHAT CAUSES AURORAS?

Auroras are the result of collisions between gaseous particles (in the Earth’s atmosphere) with charged particles (released from the sun’s atmosphere). Variations in colour are due to the type of gas particles that are colliding. The most common aurora colour which is green, is produced by oxygen molecules located about 60 miles above the earth. The rarer red auroras are produced by high-altitude oxygen, at heights of up to 200 miles. Nitrogen produces blue or purple aurora.

 

How do charged particles from the sun get here?

Solar Wind

Generally, it is when there is an opening in the suns atmosphere that allows electrons and protons to flow out. In terms of auroras, we need quite a lot of charged particles colliding with earth’s atmosphere to create vivid displays, so this usually requires quite a large opening, such as a coronal hole, or a sunspot. The connection between Auroras and sunspot activity has been suspected since about 1880. Thanks to research conducted since the 1950′s, we now know that electrons and protons from the sun are blown towards the earth on the ‘solar wind’.

When the charged particles are blown towards the earth by the solar wind, they are largely deflected by the earth’s magnetic field. However, the earth’s magnetic field is weaker at either pole and therefore some particles enter earth’s atmosphere and collide with gas particles. These collisions emit light that we perceive as the dancing lights of Auroras.

The lights of the Aurora generally extend from 80 kilometres (50 miles) to as high as 640 kilometres (400 miles) above the earth’s surface.

 

WHERE IS THE BEST PLACE TO WATCH AURORA?

Because the phenomena occurs near the magnetic poles, getting as close to these poles as possible will rapidly increase the chances of viewing aurora. As the magnetic south pole is in Antarctica, unless your a scientist working there, it usually leaves the northern hemisphere the most sensible option of viewing aurora. It should be mentioned however that during strong solar storms, aurora australis are quite often visible in places south from Australia. But generally speaking, the best places to watch the aurora are usually are North America or Europe.

In North America, the north western parts of Canada, particularly the Yukon, Nunavut, Northwest Territories and Alaska are favourable. In Europe, Scandinavia, particularly the Lapland areas of Norway, Sweden and Finland is very good for aurora viewing. Iceland is also a good place for auroras and Auroral displays can also be seen over the southern tip of Greenland.

In terms of what physically makes a place good to view aurora aside from the proximity to the magnetic poles. The most important point is ‘light pollution’, it will ruin any aurora show, so the best places to watch the auroras should be away from light pollution. In most cases in the north this usually only requires driving for 30 minutes of a city/town and you should be in light pollution free skies.

The other most important is to be on relatively high ground with an un-obscured view north (this is not necessary if you are so far North the auroras are usually directly overhead). The further away from the north pole you are, generally speaking the lower on the horizon the aurora will be. Of course this depends on a lot of factors such as aurora strength (Kp level).

Those are really the main points to successful aurora viewing, if you get them all right, then you should be in for a good show. Of course if there are clouds, then forget all the above! Auroras are not visible through most types clouds.

The following graphic shows what strength Kp is needed to view aurora where you are. For the current Kp strength, check our forecast page:

kp-map

 

WHEN IS THE BEST TIME TO WATCH FOR AURORAL DISPLAYS?

Whenever there is a significant event on the sun and it is earth facing, it usually means a great aurora show is in the offing. There are times when the sun is very quiet and there are times when it is very active. This is known as the solar cycle. The solar cycle is 11 years. It has a solar minimum period and a solar maximum period, it is the solar maximum period when it is at it’s most active. The next peak period aka solar max is late 2013.

Winter in the north is generally a good season to view lights. The long periods of darkness and the frequency of clear nights provide many good opportunities to watch the auroral displays. Usually the best time of night (on clear nights) to watch for auroral displays is between 10pm to 2am. Although they can, and quite often are, seen either side of these times.

Some great videos:

Comments are closed.