Today’s article is about the Aurora, which appears at the North and South poles. Written by our first contributor, Reem Taibah. If you like this article, help us by sharing it on Twitter and Facebook.
Aurora is the shade of colors or oval shaped light that can be seen in the night sky. It’s a natural phenomenon that appears in the dark skies of the night, specifically near the poles of the earth. In the Northern pole it’s called “Aurora Borealis” and in the Southern pole it’s called “Aurora Australis”. The Aurora name comes from the Roman goddess of dawn “Aurora,” and Borealis/Austrealis is the Greek meaning of North-wind and South-wind respectively.
Aurora happens due to the interaction of solar wind particles with the earth’s atmosphere releasing the energy that we see as light. The Solar wind is a stream of energetic particle that comes from sun, and travels at high speeds an average of 50 Km/s. When these energetic particles (mostly electrons and protons) hit the earth’s ionosphere, which is the outermost layer of the earth’s atmosphere, they excite the particles of the ionosphere giving electrons more energy.
After a certain time, when the electrons degrade to a lower energy level, particles release a certain amount of energy with certain frequency depending on the energy emitting particle (oxygen or nitrogen, in the form of either atoms or molecules) and this resulting energy released from the process is what we see as light in the sky. Each frequency is responsible for the color of light, or what is known as the Spectral Lines Emission. The Oxygen molecule is responsible for the green emission, the Nitrogen molecule is responsible for blue emission and atomic oxygen is responsible for the red color emission.
The reason Aurora only happens at the northern or southern pole of the globe is because those charged particles from the solar wind follow the magnetic field lines of the earth that ends or starts at the pole. The Aurora can actually happen daily but might not be visible with the naked eye. More solar wind interaction with the atmosphere is needed to generate the bright color. This usually happens at the height of 90-130 Km above sea level, but can also happen at different heights based on solar wind strength. One factor that plays a major role in increasing the aurora’s light are Sunspots, which are areas high nuclear activity in the sun that emit more energetic and faster particles to reach earth and interact with the ionosphere, the sunspot cycle happens every 11 years which is the time it takes the sun to round itself.
There are two types of aurora; the first is “Discrete,” (right) which is when you see stripes of light waving in the dark sky. The second is “Diffuse,” (left) when there are wave-particle interactions in the atmosphere and particles are distracted, you see a smooth layer of light instead of concentrated threads.
There are also many colors based on the atomic composition of the atmosphere as we’ve explained previously. Aurora borealis seasons in (Alaska, northern Canada, Greenland, Iceland, Norway, Sweden, Finland and Siberia) is from August through April, and can be seen at around 50 latitude. Last but not least, this phenomenon does not happen only on planet earth but also on other solar system planets with a magnetic field like Jupiter and Saturn.
About the writer: Reem Taibah is a recently graduated physicist, with interest in high energy physics. She also does crochet.