Wolf_Bassist wrote:
This just in: Before coming here today (more like tonight), I came across this article on the news section of my homepage. Apparently, the mystery of the aurora borealis may have been solved. The link for the article is posted below.
http://www.comcast.net/articles/news-ge ... rn.Lights/Quote:
Scientists have exposed some of the mystery behind the northern lights. On Thursday, NASA released findings that indicate magnetic explosions about one-third of the way to the moon cause the northern lights, or aurora borealis, to burst in spectacular shapes and colors, and dance across the sky.
That must be some of the most silly things I have ever heard.
As I said earlier: Auroras are produced by the collision of charged particles from Earth's magnetosphere, mostly electrons but also protons and heavier particles, with atoms and molecules of Earth's upper atmosphere (at altitudes above 80 km). The particles have energies of 1 to 100 keV. They originate from the Sun and arrive at the vicinity of Earth in the relatively low-energy solar wind. When the trapped magnetic field of the solar wind is favourably oriented (principally southwards) it reconnects with Earth's magnetic field, and solar particles enter the magnetosphere and are swept to the magnetotail. Further magnetic reconnection accelerates the particles towards Earth.
The collisions in the atmosphere electronically excite atoms and molecules in the upper atmosphere. The excitation energy can be lost by light emission or collisions. Most aurorae are green and red emission from atomic oxygen. Molecular nitrogen and nitrogen ions produce some low level red and very high blue/violet aurorae. The light blue colors are produced by ionic nitrogen and the neutral nitrogen gives off the red and purple color with the rippled edges. Different gases interacting with the upper atmosphere will produce different colors, caused by the different compounds of oxygen and nitrogen.
Typically the aurora appears either as a diffuse glow or as "curtains" that approximately extend in the east-west direction. At some times, they form "quiet arcs"; at others ("active aurora"), they evolve and change constantly. Each curtain consists of many parallel rays, each lined up with the local direction of the magnetic field lines, suggesting that aurora is shaped by Earth's magnetic field. Indeed, satellites show electrons to be guided by magnetic field lines, spiraling around them while moving towards Earth.
The curtains often show folds called "striations", which are curtain-like. When the field line guiding a bright auroral patch leads to a point directly above the observer, the aurora may appear as a "corona" of diverging rays, an effect of perspective.
Although it was first mentioned by Ancient Greek explorer/geographer Pytheas, Hiorter and Celsius first described in 1741 evidence for magnetic control, namely, large magnetic fluctuations occurred whenever the aurora was observed overhead. This indicates (it was later realized) that large electric currents were associated with the aurora, flowing in the region where auroral light originated. Kristian Birkeland (1908)[2] deduced that the currents flowed in the east-west directions along the auroral arc, and such currents, flowing from the dayside towards (approximately) midnight were later named "auroral electrojets" (see also Birkeland currents).
Still more evidence for a magnetic connection are the statistics of auroral observations. Elias Loomis (1860) and later in more detail Hermann Fritz (1881)[3] established that the aurora appeared mainly in the "auroral zone", a ring-shaped region with a radius of approximately 2500 km around Earth's magnetic pole, not its geographic pole. It was hardly ever seen near that pole itself. The instantaneous distribution of auroras ("auroral oval", Yasha/Jakob Feldstein 1963[4]) is slightly different, centered about 3-5 degrees nightward of the magnetic pole, so that auroral arcs reach furthest towards the equator around midnight. The aurora can be seen best at this time.
Referrences:
[2] - Birkeland, Kristian (1908). "The Norwegian Aurora Polaris Expedition 1902-3." (book)
[3] - Fritz, Hermann (1881). "Das Polarlicht." (book)
[4] - Feldstein, Y. (1963). "Some problems concerning the morphology of auroras and magnetic disturbances at high latitudes", Geomagnetism and Aeronomy, 3, 183-192. (book)
In case you didn't notice, this was all copy-pasted from Wikipedia. I highly recommend buying and reading those three books, by the way. They are very interesting.
