NATS 1870 Lecture Notes - Lecture 9: Aurora, Solar Wind, Stellar Magnetic Field
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SC/NATS 1870 Understanding Color 01/30/2013
What are they?
•means “dawn” in Latin
•are beautiful displays of colored lights in the sky at Northern and Southern latitudes
•Northern lights = aurora borealis
•Southern lights = aurora austratis
•produced by interaction between the sun (particular the solar wind) and the earth’s
•auroras would have an emission line spectrum, produced like the nebulas
•solar wind particles - they are charged and so have an attraction to the earth’s
•it is a luminescent interaction
•there needs to be an input of energy to raise up electrons to higher levels
- transfer of kinetic energy
•the colors of the aurorae depend on the speciﬁc molecules that are excited by the
charged solar wind particles
- one solar wind particle can be responsible for exciting several molecules
•blue color - comes from ionized nitrogen (120-180 km altitude) !
- solar wind particles can knock off electrons from the nitrogen molecules and
create what are called “secondary electrons” (ones that aren’t from the solar win) !
- these secondary electrons can then transfer their own kinetic energy to oxygen
molecules lower in the atmosphere which creates the most common aurora color !
- this interaction generates the most common auroral color (green) and is produced
by558nm emission from molecular oxygen
•red color - often has nitrogen which gives off the red emission!
- the lower edges on aurorae often have a red color, due to molecular nitrogen at
- the red color at higher altitudes arises from ionized oxygen !
- this is quite rare and needs particularly energetic solar wind particles
•the colors overall are determined by the composition of the atmosphere which
changes with height or altitude
•auroral activity can impact the magnetic activity on earth and has caused power
outages in the past
•the aurora can also deposit heat into the earth’s atmosphere from the kinetic energy of
the solar win particles, heating the atmosphere!
- parts of the atmosphere that are hotter and colder create pressure !
- can become dissipated as infrared !
- can also provide a source of energy for winds in the earth’s atmosphere
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