AURORA BOREALISFadhila Salsabila

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Name and OriginsHistoryNorthern Light TimesMorphing the Magnetic FieldForming of AurorasThe Aurora OvalAurora FormsDancing ColoursSources

Name and OriginsName: Aurora Borealis Latin for Northern DawnOne of the most impressive natural phenomena First recorded incident: La Caverne de Lascaux SW FranceFascinates and terrifies humansAurora Legends: Every northern culture has oral legends about the aurora, passed down for generations

*Ancient Eskimo stories often are associated with notions of life after death. Some thought that the aurora was a narrow and dangerous pathway for the departed souls to heaven.

Medieval AgePeople believed that the polar light is a bad omenFearing the red lightEspecially while it is very rare in Middle Europe The aurora was for example described as heaven battles or as candles

Fridtjof NansenThis Norwegian polar explorer tried to reach the north pole with his ship Fram in 1895-96He was blocked by ice but made many woodcuts and drawings about the auroraFridtjof Nansen 1861-1930Image source: gedds.pfrr.alaska.eduImage source: gedds.pfrr.alaska.edu

Northern Light TimesSolar phenomenon in the IonosphereOccurs while periods of high solar activity80-200km above ground connected to the magnetosphere

Solar WindsSolar winds are caused by energy released by the sunExtension of Suns coronaHigh speed plasma

A long way towards earthInteractions with the Ionosphere solar wind (speed 450km/h) carries a weak magnetic field Interaction between this and the magnetic field of earth Changes form of the earths magnetosphereenergy dissipates into gaseous form, causing Auroras or stays in electric formDangers: Interrupting satellite transmissions / power grids

Morphing the magnetic field earth has a magnetosphere surrounding the planet solar wind flowing past the earth solar wind and the magnetosphere are two electrically

conducting fluids with magnetic fields plasma and atoms collide energy flow causes a change in magnetic field

Image Source: http://odin.gi.alaska.edu/FAQ/

MagnetosphereEarth has a dipole magnetic field similar to a bar magnetInvisible magnetic field lines entering at the north pole, exiting at the south poleperiods of high solar activity interaction between the solar wind and magnetosphere solar winds effect the comet shape

Bare MagnetImage source: gedds.pfrr.alaska.eduImage source: wikipedia.com

Forming of AurorasRepeat: solar wind collides with atoms of the upper atmosphereAltitudes of 80-200kmFrequency usually follows the 11-year sunspot maximum cycle.Peak 3 years after the peak of the sunspot cycle.

The Aurora OvalThe aurora is often visible at high latitudes Magnetic field pressure is strongest Most often: Oval located between 65 and 75 degrees latitudeOval ranges from 500 to 1500 km in width Zone statistically defined

A aurora seen from spaceNasa

Where the aurora can be seenNumber of nights per year aurora can be seen at certain locationsNorthern Norway:

100 nights each per yearRest of Norway:

10 nights every yearMiddle Europe:

1 to 0,1 nights each yearshttp://gedds.pfrr.alaska.edu/aurora/Images/w1.jpg

Simple aurora structure elements

Complex formationsComplex formations out of the shown elements:Curl CurtainOmega bandCoronaPulsating aurora

Combinations are also possible

Why colourfull?High-speed discharge electrons collide with atoms and molecules in the upper atmosphereDifferent kinds of atoms and molecules produce different colours of lights Emissions between 100 and 300 km altitude

Dancing Colours

>500km:

Hydrogen and Helium atoms take over200-500km:

Oxygen atoms green / brownish-redbrightest single line emission of the aurora100-200km:

Nitrogen molecules blue / redblue/purple border Green line emission (oxygen) is quenched at this altitude The color of light emitted depends on the wavelength ofa photon: visible light ~400-700 nanometers (blue-red)

Auroras on other planetsPlanets with magnetic fields have AurorasJupiter, Saturn have highest concentrationsCaused by Solar WindsNASA image of Jupiter aurora in UV, Hubble Space Telescope:

*Ancient Eskimo stories often are associated with notions of life after death. Some thought that the aurora was a narrow and dangerous pathway for the departed souls to heaven.