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Auroras

Aurora

Introduction

Jupiter, the fifth planet from the sun, is probably the most remarkable planet in the solar system. But, have you ever stopped and asked yourself, “How did Jupiter get its name?”. In Roman mythology, Jupiter was known as the supreme God, the King of All Gods. Since Jupiter is the largest planet in the solar system, it appears that the name suits the planet well. So, does this mean that the names of other planets in our solar system were also derived from Roman mythology? Absolutely! Roman mythology, however, did not give names to just planets in our solar system. Roman mythology also gave rise to other Gods and Goddesses, such as Cupid (God of Love), Bacchus (God of Wine) and Aurora (Goddess of Dawn). The Goddess Aurora and Boreas (Greek god of the wind) are the namesakes of the natural phenomenon Aurora Borealis, commonly referred to as the Northern Lights.1,2 The Northern Lights are characterized as a wonder of colored lights in the sky near the northern pole. These same wonders of light also occur at the south pole, known as Aurora Australis, or The Southern Lights.3 Emission of these beautiful bands of light are a way that our planet displays electrical connectivity to the sun.

How is The Sun Involved?

The electrons and protons that come from the sun’s solar flares and coronal mass ejections are the energy source for the aurora.2 The coronal mass ejections, or CME, are massive explosions of solar plasma and magnetic fields driven toward the earth by solar flares.2 This pathway is known as the solar wind.2 The solar wind comes into contact with Earth’s magnetosphere (the region surrounding Earth and Earth’s magnetic field, comprised of trapped charged particles controlled by the magnetic field), forming a boundary known as the shock front. 2,3 This encounter also results in the formation of a plasma sheet on the side of the earth facing away from the sun (the night side). Plasma is a form of matter, an ionized gas, in which electrons and ions coexist. So, a plasma sheet is sheet of plasma found in the tail of the magnetosphere.1 In this region, the particles are maintained and periodically stimulated and forced toward earth at high velocities. These particles then move along earth’s magnetic field lines and are eventually attracted to Earth’s magnetic poles.1

The fluctuations and divergence of the solar wind ultimately delegate the amount of energy released into the magnetosphere.2 The incoming energy is transformed into electromagnetic energy as well as electrical currents, which are saved in the magnetosphere’s tail.2 If the energy entering the magnetosphere is too substantial or too extensive, the magnetosphere may lose its equilibrium. 2,3 In order to regain equilibrium, it must release this excessive energy. Much of this relinquished energy aids in the acceleration of electrons.1 When the magnetic field directs the electrons from the magnetosphere’s tail into Earth’s atmosphere, the aurora is produced.3 Since the magnetosphere’s tail lies on the side of the Earth facing away from the sun (the night side), auroras occur more dynamically and beautifully closer to midnight.1,3

The Display of Auroras

When the fast-moving electrons from the magnetosphere collide with the oxygen and nitrogen molecules found in earth’s upper atmosphere, the resulting display is the aurora.1,3 The electrons are responsible for “exciting” the oxygen and nitrogen molecules by transferring energy to them. What does it mean for a molecule to exist in an excited state? This simply means that an electron in the molecule has absorbed enough energy to put it into a higher energy state. Eventually, the excited electrons will relax back to their original state by releasing energy in a form of a photon (a small particle of light). A single photon itself is far too small to be seen individually.3 However, the electrons in the magnetosphere hit the oxygen and nitrogen molecules, which in turn emit an innumerable amount photons.3 The many photons released through this collision become visible to the eye, giving us the display of the aurora.2 The most common color produced by an aurora is a pale yellowish-green, produced by oxygen molecules located about 60 miles above the earth. 2,3 Red auroras are deemed rare and are generated by high-altitude oxygen, at heights of up to 200 miles. Nitrogen produces blue or purplish-red aurora.2,3

O2+ + energy (from e- ) --> O2* --> O2 + light (green-yellow)

N2+ + energy (from e- ) --> N2* --> O2 + light (blue-purplish/red)

References

  • Seybold, Paul G., Lemont B. Kier, and Chao-Kun Cheng. "Aurora Borealis: Stochastic Cellular Automata Simulations of the Excited-State Dynamics of Oxygen Atoms." International Journal of Quantum Chemistry 75 (1999): 751-756.
  • Leon, Nancy. "What Is An Aurora?" http://spaceplace.nasa.gov/aurora/en/ (accessed Oct. 25, 2016).
  • Brekke, Pal. "Secrets of the Northern Lights." Sky & Telescope. Feb. 2013, Vol. 125 Issue 2, p 18-25.
  • HistoryTVAU. "First Recorded Sighting of Aurora." http://www.historychannel.com.au/this-day-in-history/first-recorded-sighting-of-aurora/ (accessed Nov. 4, 2016).