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Photo by Ruslan Merzlyakov. Visit him on Facebook.
What causes the aurora borealis or northern lights? earthsky.org /earth/whatcausestheauroraborealisornorthernlights
By Eleanor Imster
Those who liveat or visit highlatitudes mightat timesexperiencecolored lightsshimmeringacross thenight sky.Some Inuitbelieved thatthe spirits oftheir ancestorscould be seendancing in theflickeringaurora. InNorsemythology, theaurora was afire bridge tothe sky built bythe gods. Thisetherealdisplay – theaurora borealisor auroraaustralis, thenorthern orsouthern lights– is beautiful.What causesthese lights toappear?
Our sun is 93 million miles away. But its effects extend far beyond its visible surface. Great storms on the sun sendgusts of charged solar particles hurtling across space. If Earth is in the path of the particle stream, our planet’s magneticfield and atmosphere react.
When the charged particles from the sun strike atoms and molecules in Earth’s atmosphere, they excite those atoms,causing them to light up.
What does it mean for an atom to be excited? Atoms consist of a central nucleus and a surrounding cloud of electronsencircling the nucleus in an orbit. When charged particles from the sun strike atoms in Earth’s atmosphere, electronsmove to higherenergy orbits, further away from the nucleus. Then when an electron moves back to a lowerenergyorbit, it releases a particle of light or photon.
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When charged particles from the sun strike air molecules in Earth's magnetic field, they cause those molecules' atoms to becomeexcited. The molecules give off light as they calm down. Image Credit: NASA
What happens in an aurora is similar to what happens in the neon lights we see on many business signs. Electricity isused to excite the atoms in the neon gas within the glass tubes of a neon sign. That’s why these signs give off theirbrilliant colors. The aurora works on the same principle – but at a far more vast scale.
The aurora oftenappears ascurtains of lights,but they can alsobe arcs or spirals,often followinglines of force inEarth’s magneticfield. Most aregreen in color butsometimes you’llsee a hint of pink,and strongdisplays might alsohave red, violetand white colors.The lights typicallyare seen in the farnorth – the nationsbordering theArctic Ocean –Canada andAlaska,Scandinaviancountries, Iceland,Greenland andRussia. But strong displays of the lights can extend down into more southerly latitudes in the United States. And ofcourse, the lights have a counterpart at Earth’s south polar regions.
The colors in the aurora were also a source of mystery throughout human history. But science says that different gasesin Earth’s atmosphere give off different colors when they are excited. Oxygen gives off the green color of the aurora, forexample. Nitrogen causes blue or red colors.
So today the mystery of the aurora is not so mysterious as it used to be. Yet people still travel thousands of miles to seethe brilliant natural light shows in Earth’s atmosphere. And even though we know the scientific reason for the aurora,the dazzling natural light show can still fire our imaginations to visualize fire bridges, gods or dancing ghosts.
Bottom line: When charged particles from the sun strike atoms in Earth’s atmosphere, they cause electrons in theatoms to move to a higherenergy state. When the electrons drop back to a lower energy state, they release a photon:light. This process creates the beautiful aurora, or northern lights.
Eleanor Imster
Eleanor Imster has helped write and edit EarthSky since 1995. She was an integral part of the awardwinning EarthSkyradio series almost since it began until it ended in 2013. Today, as Lead Editor at EarthSky.org, she helps present thescience and nature stories and photos you enjoy. She also serves as one of the voices of EarthSky on social mediaplatforms including Facebook, Twitter and G+. She and her husband live in Tennessee and have two grown sons.
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Jennifer Khordi captured this aurora on September 7, 2015 over the Catskills of New York state. Visit Jennifer Khordi on Facebook.
Aurora just west of Saskatoon, by Colin Chatfield. He said, “We were just about to leave as the Aurora was just a dull band, then itcame alive for about an hour or so. This was taken at 2:02am on January 27, 201] … It is not very visible, but I caught Comet Lovejoy
at centre left of this photo.”
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“This photo was captured a couple of hours ago in Nordreisa, Norway. I was dressed in my very best winter clothes and I can easilyadmit that I was freezing most of the time anyways, 22 below (7.6 fahrenheit) kinda has that effect.” January, 2015. © 2015 TorIvar
Næss
Aurora in Vesterlålen, Norway by Stig Hansen
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Aurora borealis over Norway’s Steinvikholmen Castle by Hallvor Hobbyfotograf Lillebo.View larger. | Photo credit: HallvorHobbyfotograf Lillebo
Reisafjorden, Norway bathing in auroras on January 2, 2014. When charged particles from the sun strike atoms in Earth’satmosphere, they cause electrons in the atoms to move to a higherenergy state. When the electrons drop back to a lower energy
state, they release a photon: light. This process creates the beautiful aurora, or northern lights. Image copyright 2014 TorIvar Næss.Via WaitForIt on Facebook.
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View larger. | Mike Taylor calls this photo Moonlight Aurora II. He captured it on February 19, 2014. Visit Taylor Photography
View larger. | Aurora over Mt. Hood in Oregon as captured by Ben Coffman Photography during the night of May 31June 1, 2013.Visit Ben’s photography page on G+ or visit Ben on Facebook.
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Aurora on January 1, 2014 by GeirInge Bushmann. The lights typically are seen in the far north – the nations bordering the ArcticOcean – Canada and Alaska, Scandinavian countries, Iceland, Greenland and Russia. See more photos from GeirInge Bushmann
View larger. | Aurora seen by EarthSky Facebook friend Colin Chatfield in Saskatchewan, Canada on May 19, 2012.