Dancing Lights In The Night Sky

Mar 23, 2015 By Deepa Gopal
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On St. Patrick's Day last week, the skies threw up a spectacular display of green and red as well in Northern parts of the U.S, Canada, and Europe.

Residents in the U.S states of Minnesota, Wisconsin, Alaska, Washington, North and South Dakota reported seeing the lights before dawn last Tuesday. Even the International Space Station (ISS) captured images of the breathtaking light display.

Known as the Aurora Borealis or Northern Lights, they are caused by a sudden ejection of charged particles by the Sun. To understand how they form, let's look at the science behind solar storms and its interaction with our Earth's magnetic field. 

What Is A Solar Wind?

Our Sun is constantly sending out a steady stream of charged particles into the interplanetary space, known as a solar wind. Sometimes, during periods of intense solar activity, a solar flare can be observed -- this is a sudden outburst of charged particles from the sun's corona, its outer layer. Scientists call this Coronal Mass Ejection or CME, though it is not understood what causes it.

CME's are propelled outwards from the sun at speeds of 50-2000 kilometers per second! These flares can be intense enough to disrupt our satellite communication systems. Two blasts of magnetic plasma left the sun on Sunday, March 15th, combined and arrived on Earth about 15 hours earlier and much stronger than expected. It is the most powerful solar storm to blast Earth since the fall of 2013.

The Role Of Our Earth's Magnetic Field

The charged particles from the Sun alone cannot create these spectacular Northern Lights. As we all know, our Earth has a magnetic field that is strongest around the poles. When the charged particles from the sun hit the Earth's atmosphere, they are directed towards the poles by the Earth's magnetic field -- much like water flows around a stone.

At the poles, they collide with the oxygen and nitrogen atoms in the atmosphere, causing them to get excited. When these atom return from the excited state back to the normal state. they emit a photon of light (similar to lasers).

Different colors are produced, depending on the atoms that the particles collide with. Oxygen generally produces colors ranging from green to brown, and nitrogen produces shades of red and blue. Since the intensity of the light produced is low, the auroras can only be seen at night time.

More often than not, we hear of the displays in countries close to the North pole, but it is equally common in the South pole. Known as Aurora Australis, they are mostly seen over the continent of Antarctica, which is lightly populated.

Do you live in any of the Northern U.S cities or in countries close to the North pole? Did you see the Dancing Lights?