Light Polluted Skies

I was interested to know what it was possible to achieve from the severely light polluted skies of suburban London. Was it was possible to image the Horsehead Nebula in the Orion's belt area of the sky.

I used a Canon EOS 300D digital SLR with a 50mm f1.8 lens guided by a Celestron 130 SLT alt/azimuth mount so it followed the Orion constellation across the sky. Being an alt/azimuth mount (instead of equatorial) the constellation is still rotating relative to the camera.

230 exposures of 30seconds were taken i.e. nearly 2 hours of total exposure.

Here is a single 30 second exposure:


Notice how severe the light pollution is (the orange glow).

Here is the area of the Orion Nebula and the Horsehead Nebula:


The Orion Nebula is just beginning to show above the ambient light pollution. But nothing can be seen of either the Horsehead Nebula or the Flaming Tree Nebula. I later calculated that the light pollution was over 100x brighter than the Horsehead Nebula.

After rotating and stacking 230 images (using the IRIS software), this was the result before further processing.


This is the final image after subtracting the light pollution (click on it to see it full size). The image uses logarithmic scaling of intensity in order to show the whole dynamic range.


The Horsehead Nebula is just about discernable in the above image. But remember it is 100x fainter than the light pollution that has just been subtracted.

It is very interesting to see the results of stacking 1, 4, 16, 64 and 230 images - each time subtracting the light pollution. Watch how the image appears out of the noise:

1 image:


4 images stacked:


16 images stacked:


64 images stacked:


230 images stacked: