The colours of aurora borealis ("Northern Lights") or aurora australis
("Southern Lights") is from a form of fluoresecence, caused when high-energy
electrons enter the auroral oval (sort of a weakened magnetic "doughnut" about
2,500 km from the north and south magnetic poles) after being diverted towards
it by the Earth's magnetic field. The fluoresence arises from electrons
striking oxygen or nitrogen atoms in the ionosphere.
Oxygen gives green and (less common) red auroral displays; violet (from
nitrogen) is quite rare -- at Edmonton's latitude (53 degrees 30 minutes N)
I've only seen the violet displays *once*. We get the auroras lots during the
spring and fall months, but it's sometimes too damn cold to go out and look at
'em during "high winter" here.
Best bets? As with all night-sky photography, get away from cities that are
between you and the northern horizon (if you're in the Northern hemisphere,
natch), as the glow will pretty much wipe out any auroral display, or make it
look suspiciously like light clouds (my wife and I have had arguments around
this point -- "Those are just clouds!" "It's the aurora, honey." "You're full
of it." "Yes, well, we know that, but let's try to stay on point, shall we?").
I don't think I'd use Kodachrome. First off, the "detail" in auroras is very
low anyways, and you want to capture as short a duration as possible to try and
preserve some interesting structure in the image (longer exposures just give a
blur). I'd probably try high-speed Ektachrome (or other E-6 film) of some
sort. There have been discussions before on this list about best films,
reciprocity characteristics, etc. which I'm not qualified to get into -- I'd
just experiment. Perhaps Lee Hawkins can give more info here.
Garth
"A bad day doing photography is better
than a good day doing just about
anything else."
The Unofficial Olympus Web Photo Gallery at:
http://www.taiga.ca/~gallery/
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