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What is Aurora?• Natural light display in
the sky• Mostly in the polar
region• Observed at night• Typically occurs in
ionosphere
What causes Aurora?
• Energetic charged particles from magnetosphere• Immediate cause: precipitating energetic particles
(electrons/protons that are energized in geospace)• This process draws its energy from the interaction of
Earth’s magnetosphere with the solar wind• Energy is transferred from solar winds to
magnetosphere– Magnetosphere responds to reconnection by dumping
electrons/protons into the high latitude upper atmosphere where energy of plasma can be dissipated resulting in aurora
What causes the color?
• Composition & density of the atmosphere & the altitude of the aurora determine possible light emissions
• Excited atom/molecule returns to ground state & sends a photon with a specific energy
• Energy of the photon Color• Energetic electrons can split molecules of air into
nitrogen & oxygen atoms• Photons of aurora have signature colors of
nitrogen/oxygen
Color Example:
• Oxygen atoms strongly emit photons in two colors: – green and red, red is brownish that is at the limit of what the
human eye can see
• Red auroral emission is very bright, we can barely see it
Photographic Film
• See more red aurora on photos than with unaided eye
• More atomic oxygen at high altitudes red aurora tends to be on top of the regular green aurora
• Colors are a mixture of all the auroral emissions• Overall impression is a greenish-whitish glow• Very intense aurora gets a purple edge at bottom
(purple: mixture of blue and red emissions from nitrogen molecules)
Altitude• Bottom edge 100 km altitude• Altitude where the mission comes from depends
on the energy of the energetic electrons that make the aurora
• More energy the deeper the electron gets into the atmosphere
• High altitude aurora: 600 km (350 miles)about where space shuttle flies
Shape• Magnetic field confines motion of auroral electrons• The charged particles can only move freely when
parallel to magnetic field (in the direction of or against)• Near earth: motions of electrons are guided by Earth’s
magnetic field• An electron spirals along into the atmosphere, it stays
on/near this field line even when it makes a collision curtain shape
About Aurora Borealis
• Named after Roman goddess of dawn• Thought to be produced by sunlight
reflected from snow/ice or refracted light
• Become brighter, more distinctive, & spread over larger area two days after solar activity
• Often occur near equinoxes
About Aurora Borealis
• Cause: radiation emitted as light from atoms in upper atmosphere as they’re hit by fast moving electrons & protons
• Energy particles from sun collide with Earth’s magnetic field
• Kind of atom determines color
Anywhere else?• Aurora can be found on other
planets• Venus: has no magnetic
field irregular shaped aurora• Saturn, Earth, Jupiter: has an
intrinsic magnetic dipole field oval shaped crowns of light on both hemispheres
Video
• http://www.youtube.com/watch?v=YJBrMXSn-hU
Works Cited
• "Aurora FAQ." Aeronomy and Auroral Physics at the GI. Web. 07 Mar. 2011. <http://odin.gi.alaska.edu/FAQ/>.
• "Northern Lights - Aurora Borealis." Fairbanks Alaska Visitor Information Site. Web. 07 Mar. 2011. <http://fairbanks-alaska.com/northern-lights-alaska.htm>.
• "The Northern Lights - Where, When and What." Tromsø Geophysical Observatory. Web. 07 Mar. 2011. <http://geo.phys.uit.no/articl/nord_eng.html>.
• Stern, David P. "Secrets of the Polar Aurora." Educational Web Sites. Web. 07 Mar. 2011. <http://www.phy6.org/Education/aurora.htm>.