Aurora

6th-7th April 2000

As seen from Sharnbrook: a great display!

Photos were taken from 20:51 - 01:10 UTC, with OM10 SLR and mostly 1600 ASA Fuji Provia Film.
The display became so remarkable, the whole sky, including the south aspect was full of aurorae!


       

       

       

   





Cygnus up to Draco







Cygnus












Lyra and Cygnus













Bootes












































Corona Borealis and Hercules




































Auriga and Gemini (dodgy focus due to ill-fitting 28mm F2.8 lens!)
21:52 UTC; 1600 ASA Fuji Super HG film on OM10 SLR







1600 ASA Fuji Super HG film on OM10 SLR




15th July 2000

As seen from Sharnbrook, remarkably in the light of a nearly Full Moon!


                                     
                                      


             
Above left: Aurora Borealis 15th July 2000   Above right: sunspot group that caused the aurora as seen on 13th July 2000.




Early hours of 27th August 1998

As seen on holiday in the Lleyn Peninsula, North Wales.

                


        


29th October 2003

As seen from Sharnbrook following an unexpected surge in solar activity.
The geomagnetic storm was subsiding by the time it was dark, so this is the mere tail
end of a good display.

    





My first experiences of the aurora

As seen from Barton-le-Clay and sketched in one of my log books.
Forgive the spelling error!






Auroral Types and Colours

G
glow

Glow with no other structure, often lying low above poleward horizon. This may often
be confused with light pollution!



A
arc

Arc structure, an arch of light spanning east-west across the sky. May be homogeneous
(HA) or rayed (RA).



B
band

Folded, ribbon-like structure, often developing from an arc. May have HB or RB.

       


       


               



R
rays

Rays may sometimes be seen in isolation or bundles when no other aurora is present.




V
veil

A background veil which sometimes pervades the sky during auroral displays.




P
patches

Discrete patches (sometimes referred to as 'surfaces') of auroral light. May appear
as HP or RP.



corona


I couldn't resist this last one! The corona in Corona Borealis!

N

Auroral light, not identifiable, seen for example through cloud.


The Colour of Aurorae

The coloured light of aurorae is produced by the excitation of atmospheric atoms and
molecules when energetic electrons from the Sun (often produced in solar flares)
penetrate the Earth's protective magnetic 'shield' known as the magnetosphere.

Green Aurorae
Due to emission at a wavelength of 557.7nm from excited oxygen atoms* (OI) at an
altitude between about 90 and 150km. In mid-latitudes, this is the lowest level aurora
and can be seen in some of my photos lying below the red aurora.
*Oxygen molecules (O2) are split into atomic oxygen at altitudes above about 80km
by solar UV. This is called photodissociation.

Red Aurorae
At altitudes above 150km the aurora produced by excited oxygen atoms (OI) is red
rather than green as it is caused by emission lines at 630 and 636.4nm. Since red
aurorae are produced at higher altitudes, it is common during an auroral display to see
the red component of the aurora sitting on top of the green.

The colours appear at different altitudes because the electronic transition responsible for
the production of red light has a long lifetime of 110s, whereas for green it is only 0.74s.
Below about 150km, the atmosphere is dense enough that the atoms are disturbed by
collisions with other atoms and electrons before the red emission occurs, and so only
green may be seen. Above 150km, green is still emitted but is swamped by the red
emissions. Below about 90km, even the atoms emitting green light are disturbed by
collisions before they can do so.

During very intense displays, keep an eye out for a red tinge low down. This is due to
emission from atomic nitrogen at 70 - 100km altitude.

Violet-Purple Aurorae
At a typical altitude of 1000km, nitrogen molecules, ionised by UV from the Sun (N2+)
produces violet purple emissions when excited by incoming accelerated electrons. This
is the uppermost region of an auroral display and may only be in the earth's shadow
(and therefore visible) at certain times of the year.