AURORA BOREALISKilian Schönberger

December 2009

SAS 8 – Norwegian Area Studies

Content

1. Name and Origins

2. History

3. Northern Light Times

4. Morphing the Magnetic Field

5. Forming of Auroras

6. The Aurora Oval

7. Aurora Forms

8. Dancing Colours

9. Sources

Name and Origins

• Name: „Aurora Borealis“ Latin for „Northern Dawn“• One of the most impressive natural phenomena • First recorded incident: “La Caverne de Lascaux” SW

France• Fascinates and terrifies humans• Aurora Legends: Every northern culture has oral legends

about the aurora, passed down for generations

Medieval Age

• People believed that the polar light is a bad omen• Fearing the red light• Especially while it is very rare in Middle Europe • The aurora was for example described as heaven battles

or as candles

Image source: gedds.pfrr.alaska.edu

Image source: gedds.pfrr.alaska.edu

Fridtjof Nansen

• This Norwegian polar explorer tried to reach the north pole with his ship Fram in 1895-96

• He was blocked by ice but made many woodcuts and drawings about the aurora

Fridtjof Nansen 1861-1930

Image source: gedds.pfrr.alaska.edu Image source: gedds.pfrr.alaska.edu

Northern Light Times

• Solar phenomenon in the Ionosphere

• Occurs while periods of high solar activity

• 80-200km above ground connected to the magnetosphere

http://ds9.ssl.berkeley.edu/lws_gems/6/images_6/ion470.jpgImage source: http://ds9.ssl.berkeley.edu/

Image source: gedds.pfrr.alaska.edu

Solar Winds

• Solar winds are caused by energy released by the sun• Extension of Sun’s corona• High speed plasma

Image Source: http://talklikeaphysicist.com/wp-content/uploads/2008/10/sun-corona-mass-

A long way towards earth

• Interactions 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 earth‘s magnetosphere• energy dissipates into gaseous form, causing Aurora’s or

stays in electric form• Dangers: 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/

Magnetosphere

• Earth has a dipole magnetic field similar to a bar magnet

• Invisible magnetic field lines entering at the north pole, exiting at the south pole

• periods of high solar activity interaction between the solar wind and magnetosphere

• solar winds effect the comet shape

Bare Magnet

Image source: gedds.pfrr.alaska.edu Image source: wikipedia.com

Forming of Auroras

• Repeat: solar wind collides with atoms of the upper atmosphere

• Altitudes of 80-200km• Frequency usually follows the 11-year sunspot maximum

cycle.• Peak 3 years after the peak of the sunspot cycle.

Image source: nasa.com

The Aurora Oval

Image Source: Akasofu, Syun-Ichi. Secrets of the Aurora Borealis

• The aurora is often visible at high latitudes

• Magnetic field pressure is strongest

• Most often: Oval located between 65 and 75 degrees latitude

• Oval ranges from 500 to 1500 km in width

• Zone statistically defined

A aurora seen from space

Nasa

Image source: http://en.wikipedia.org/wiki/File:Aurora_Borealis.jpg

Where the aurora can be seen

• Number of nights per year aurora can be seen at certain locations

• Northern Norway:

100 nights each per year• Rest of Norway:

10 nights every year• Middle Europe:

1 to 0,1 nights each years

http://gedds.pfrr.alaska.edu/aurora/Images/w1.jpg

Image source: http://gedds.pfrr.alaska.edu/

Simple aurora structure elements

Images by Tom McEwan

Image source: http://gedds.pfrr.alaska.edu/

Complex formations

Images by Tom McEwan

Complex formations out of the shown elements:• Curl • Curtain• Omega band• Corona• Pulsating aurora

Combinations are also possibleImage source: fotocommunity.de

Why colourfull?

High-speed discharge electrons collide with atoms and molecules in the upper atmosphere

Different kinds of atoms and molecules produce different colours of lights

Emissions between 100 and 300 km altitude

Image source: fotocommunity.de

Dancing Colours

>500km:Hydrogen and Helium atoms take over

200-500km: Oxygen atoms – green / brownish-redbrightest single line emission of the aurora

100-200km: 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)

Akasofu, Syun-Ichi. Secrets of the Aurora Borealis.

Auroras on other planets

• Planets with magnetic fields have Auroras• Jupiter, Saturn have highest concentrations• Caused by Solar Winds• NASA image of Jupiter aurora in UV, Hubble Space

Telescope:

Image source: http://en.wikipedia.org/wiki/File:Jupiter.Aurora.HST.UV.jpg

Sources

• Bryson, G. (2003): Nordlicht – a study of the aurora borealis, Mathematics Senior Thesis Presentation

• Blixt, E. (2006): Optical flow analysis of the aurora borealis, Trans. Geoscience and Remote sensing

• Canadian Space Agency, Aurora Borealis – Northern Lights

• University of Alaska, http://asahi-classroom.gi.alaska.edu/ (18.11.2009)

• http://wikipedia.org (18.11.2009)• http://www.fotocommunity.de (18.11.2009) Profil Thilo

Bubek• http://nasa.com (18.11.2009)