Aurora borealis.

Over Stockholm does that exist?
Aurora 951018 Aurora 000406
Aurora 940501 Aurora 000406

Gallery of  aurora pictures


The nature of the aurora.

The aurora is a phenomenon of light that occurs in the atmosphere of the Earth at an altitude of about 100 - 400 km. That part of the atmosphere is called the ionosphere. The strength of light, color and appearance can fluctuate very much.

Today the cause of the aurora is explained by that electrons and protons, which have their origin in the sun, collides with atoms and molecules in the ionosphere which receive higher energy. They are excited to a higher quantified state of energy. The atoms or molecules aren't happy with such a high state of energy and therefore get rid of it by sending out a photon with a fixed vawelength, which in the visible area is called light. The color of that light depends on which atom or molecule that gave away the light.

The most common aurora is green, and that color comes from the oxygen atom which gives off light with the wavelength of 557,7 nm.


 

Some of the auroras visible colors

Wavelength in nmAtom/moleculeAltitude in km Visible color
391,4
427,8
Nitrogen1000Purple
557,7Oxygen90 - 150Green
630,0
636.4
Oxygen>150Red
656,3Hydrogen120Red
661,1
669,6
676,8
686,1
Nitrogen65 - 90Red

 

How to photograph the aurora

You need a SLR camera with a B or T setting, a lens with an aperture of f/2.8 or faster, which is used at full stop. The lens should be a short focal one because the aurora is wide spread over the sky. You can of course use a lens with normal focal length but then you will miss the magnificent spectacle that the aurora is in the picture. You also need a tripod to mount the camera on and a shutter cable releaser, so you don't get vibrations from your hands or body.

The exposure time depends on the aurora's strength of light and dynamic. A weaker aurora does of course demand longer exposure time and depending on the sky's background light you can try 20 - 40 seconds If the aurora is stronger, then try 5 - 20 seconds. It's important to try different times so you hopefully get some good pictures. Aurora with a lot of movement demand shorter exposure time to avoid blur.

Try to capture some of the landscape in the foreground to get a reference to something recognizable. That will improve the picture.

I have tested many films both negative and slide color films with speeds between 400 and 1600 ASA from different manufacturers. The manufacturer I like the best is Kodak which I think gives me good pictures. So far I have mostly used Kodak Ektachrome 400. I have recently tested the Fuji Provia 400F and that seems to be a wonderful film for aurora photography.

After ten years of night photographing I have come up with some rules and memorized them.

Never forget to ask yourself before you begin.
1. Is the lens cap removed?
2. Is the focus on the lens set to infinity?
3. Is the lens aperture set to full stop? (If you want it that way, else in the right position).
4. Is the shutter-speed dial set to B?

Practice and memorize how to do 2 3 and 4 so you know how to do this in the dark. Else one night you will do it the wrong way.

During the photography.
1. Does the rewind knob turn when you advance the film? (To check that the film is loaded correctly)
2. Is there any dew on the lens? Check after every exposure.

And as a last piece of advice. Always have a lockable shutter release cable in reserve. The one you use will break one night. (Often at the first exposure).


 
© Mats MattssonHome