Auroras. Very Pretty. But what are they?

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Aurora Borealis over Norway.

 

In a phrase, northern and sothern lights are “picturesque particle collisions”. Read further, however, and learn what causes these mysterious, beautiful, sometimes haunting, always otherworldly seeming phenomena.

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Auroras Explained

‘As they ventured towards the South Pole last month, scientists aboard an Antarctic research vessel were lucky enough to catch a glimpse of the glowing aurora.

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Also known as the southern lights (Aurora Australis), or the northern lights (Aurora Borealis) when spotted in the northern hemisphere, auroras are bright sheets of color that appear in the midnight skies around Earth’s two poles.

Witnessing this Aurora was a stroke of luck. You have to be near the south pole at just the right time—auroras are unpredictable phenomena. This was indeed a rare sighting. The astounding variety of color displayed…the unique beauty of the blues, greens, and reds shimmering off the calm sea that night left the scientists speechless.

Appropriately, the research vessel in question, is named the Aurora Australis. Although the researchers may have been lucky, auroras are certainly not random. We know a lot about them in the 21st century; but we are always learning new things.’

Northern Lights

Eielson Air Force Base, Alaska. The Aurora Borealis, or Northern Lights, shines above Bear Lake. Early Native Alaskans believed different legends about the Northern Lights, such as they were the souls of animals dancing in the sky or the souls of fallen enemies trying to rise again. (U.S. Air Force photo by Senior Airman Joshua Strang)

 

Auroras are the result of complex interactions between physics, chemistry, the Earth, the Sun; and they follow what are known as solar cycles.

The process begins when the sun releases a powerful solar wind of charged particles (mainly electrons) into Earth’s magnetosphere (the region of space controlled by Earth’s magnetic field).

Although solar winds are constantly streaming particles towards Earth, our planet’s magnetic fields are usually strong enough to deflect them and keep the particles out of our atmosphere.

Occasionally however, a Coronal Mass Ejection (an explosion near a sunspot) occurs, streaming charged particles towards Earth in greater numbers and at faster speeds than normal.

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Solar flares, such as this one can be so intense they actually damage the instruments that took the image. Some flares are so powerful they cause what are known as Coronal Mass Ejections. These types of explosions can wreak havoc on Earth.

 

The extra energy is so powerful (explosions on the Sun can pack the force of a billion megaton nuclear bombs), it reconfigures Earth’s magnetic field. This results in electrons and protons entering our upper atmosphere, and go straight for the north and south poles—moving along magnetic field lines, much like beads on a wire.

And the sun, mind you, is no small operator. These charged particles are travelling at speeds up to 1584000km/hr (or 440km/second). As they enter Earth’s atmosphere, they smash into our oxygen and nitrogen atoms, the speed of impact causing the electrons to latch on to the oxygen and nitrogen atoms.

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Above: How Solar Wind Interacts with Earth’s Magnetosphere. The solar wind is drawn to the poles by Earth’s magnetic field lines. The magnetosphere is squashed on one side from the force of the solar wind, and elongated on the other as the force pushes the magnetic field outwards.

 

To return to their normal state, the oxygen and nitrogen atoms must get rid of the extra energy; and they do so in the form of small bursts of light, known as photons.

When these collisions occur on a large enough scale and enough photons are released, the oxygen and nitrogen emit so much light the glow is visible to the human eye.

And there you have it: an aurora.

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An Aurora Australis over the Earth’s south pole, observed from the International Space Station (ISS).

 

What causes the colors and patterns?

The color of the aurora is dependent on which gas the electrons and protons collide with and how much energy is being transferred—the faster the collision, the more photons released, the brighter the color.

When you see green, yellow or red in the sky, it means oxygen molecules have been hit. When you see blue or purple light, nitrogen molecules have been hit.

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Reykjavik City, Iceland. (arctic-images.com/ljosid/)

 

Altitude also affects the colors. Blue violet/reds occur below 60 miles (100 km), with bright green strongest between 60-150 miles (100-240 km). Above 150 miles (240 km) ruby reds appear.

Displays may take many forms, or patterns, including rippling curtains, pulsating globs, traveling pulses, or steady glows.

Auroras are often described as looking like sheets, or curtains, because the electrons and protons are guided by Earth’s magnetic field lines keeping the collisions running almost parallel to one another.

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Aurora during a geomagnetic storm. Taken from the ISS. (Wikipedia)

 

Although they may be fascinating and beautiful examples of physics, auroras are actually considered a geo-hazard for their potential to damage satellites, their ability to disrupt GPS and radio signals, and the radiation hazard they pose to astronauts.

In 1989, a Coronal Mass Ejection approximately the size of 36 Earths, erupted, hurling particles towards Earth at 1.6 million kilometers per hour. The Aurora Borealis that ensued caused electrical surges so strong they were responsible for a utility grid crash at Canada’s Hydro-Quebec power site, leaving six million Canadians without electricity for over nine hours.

Regardless of the hazards, if you want to be one of the lucky ones to witness an Aurora Borealis, there are a few places where one is more likely to occur. Alaska and Scandanavia, for instance, are both situated on the cusp of the earth’s northern magnetic pole, so they typically experience auroras multiple times a year.

To witness an Aurora Australis, you would have to travel to Antarctica!

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An Aurora Australis over the South Pole.

 

Spring and Autumn tend to be the most favorable seasons. Powerful solar winds that cause auroras tend to follow an 11-year cycle with peaks and troughs. The more solar activity, the more auroras are seen on Earth.

In the past, Auroras Borealis have been spotted as far south as Japan or Florida, but this is extremely rare. ♢

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Aurora during a geomagnetic storm that was most likely caused by a Coronal Mass Ejection from the Sun. May 2010. Taken from ISS. (Photo credit: Wikipedia)

 

For some very cool visuals, see the full-color pictogram: “Chasing the Northern Lights” immediately following the Web links below…

To learn more about auroras:

http://www.nasa.gov

http://www.spaceweather.com/

To learn more about the Antarctic voyage:

www.aad.gov.au

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(Sources: Wiki; Pinterest; University of Alaska, Geophysical Institute; https://apanache.wordpress.com/2012/12/27/auroras-space/; http://www.nasa.gov; http://www.spaceweather.com/; http://www.aad.gov.au; http://www.chiefscientist.gov.au/2011/03/picturesque-particle-collisions-auroras-explained/)

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