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Aurora Borealis: Nature’s Light Show

By Uzair Samad

Photo credit: Pixabay

What is the Aurora Borealis?

The ‘Aurora Borealis’, more commonly known as the Northern Lights is arguably one of the most breath-taking phenomena that occurs in our world. It results in a beautiful display of many different colours, such as green, red, pink and purple and has also been seen to glimmer and ‘dance’ in the sky for hours at night. It is almost like a moving painting that has been projected on to the sky. Many people from around the globe travel to countries such as Iceland, Greenland, Norway, Finland and Sweden [1] (all located near the North Pole) just to experience this amazing, natural show that lights up the sky and to tick off a key objective from their bucket-list. As with many things in Nature, there is a scientific explanation behind this beautiful show that occurs at the Earth’s atmosphere and thus its mechanism of doing so will be explored in this article.

How it happens…

It all starts from the Sun which is 93 million miles away from the Earth [3]. Large storms that occur on the surface of the Sun consequently cause solar winds to be released from it. These solar winds can travel at an extremely high speed of approximately 1 million miles per hour [3] and contain negatively-charged electrons and positively-charged protons. Upon reaching the Earth, the movement of this stream of charged particles becomes influenced by the Earth’s generated magnetic field (magnetosphere) [4]. The interaction of the charged particles and the magnetic field of the Earth consequently causes the particles to be deflected towards the Northern/Southern Poles. At the poles the strength of the magnetic field is weaker than at the Equator, and thus allowing the electrons within the solar wind to enter the Earth’s atmosphere [4].

Photo credit: Pixabay

The Earth’s atmosphere consists of a variety of gaseous atoms of different elements [3]. Common gases in the atmosphere include Oxygen and Nitrogen. Hence, when the charged particles enter the atmosphere they collide with the different atoms within it. This collision causes the different atoms in the atmosphere to be ‘excited’. Excitation refers to the movement of electrons that reside within an atom to a higher-energy level than its initial state. The excited electron can then fall back down to its initial energy level and as a result, emits a photon of light [3]. This same concept is seen in emission spectroscopy which is a vital tool used by Analytical Chemists [5].

The type of light that is emitted depends on the type of atom that is excited, the energy absorbed and in terms of this phenomenon, the altitude at which the collisions take place [2]. The Northern lights occur from 50 to 500 miles above the Earth’s surface [7]. Charged particles from the solar wind encounter Oxygen and Nitrogen atoms at altitudes of 20 to 200 miles above the Earth’s surface [2]. The most common colour observed is green, and this corresponds to the excitation of Oxygen atoms up to approximately 150 miles in altitude. The excitation of Oxygen can also occur at above this altitude level but will emit red light. Above this altitude level, a violet/purple colour is observed due to excitation of Nitrogen. The ‘dancing’ of the lights is caused by shifting electric and magnetic forces that move along the atmosphere’s current [2]. The aurora exist as an oval above the Earth’s magnetic poles. High sunspot activity can cause these ovals to extend further down South and enable it to be seen in Australia [6].

References

  1. Northern Lights Holidays https://www.discover-the-world.co.uk/destinations/northern-lights-holidays (Accessed 10/12/16)
  2. How does the Aurora Borealis work? http://science.howstuffworks.com/nature/climate-weather/atmospheric/question471.htm (Accessed 10/12/16)
  3. What causes the Northern Lights? http://earthsky.org/earth/what-causes-the-aurora-borealis-or-northern-lights (Accessed 10/12/16)
  4. What is the Aurora Borealis? http://www.aurora-service.eu/aurora-school/aurora-borealis/ (Accessed 10/12/16)
  5. Atomic spectra https://www.itp.uni-hannover.de/~zawischa/ITP/atoms.html (Accessed 10/12/16)
  6. Atmospheric optics, Aurora, Northern Lights http://www.atoptics.co.uk/highsky/auror1.htm (Accessed 10/12/16)
  7. Northern Lights Centre http://www.northernlightscentre.ca/northernlights.html (Accessed 12/10/16)

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