This mosaic of the
Andromeda galaxy, M31 was imaged over several sessions between the beginning
of October and December 2003. It comprises of 8 frames and a total exposure
time of 9 hours 40 minutes. I do not feel that this effort is as good as
the Veil Nebula mosaic. I had some difficulty getting the data for this
image due to bad weather, work and local light pollution from a nearby golf
driving range that does not turn off its lights until 20:30. When I gathered
the Luminance data, M31 was well positioned from my location meaning that
I could get a couple of frames per session before it got too low. The colour
was a different matter. Bad weather and the march of time meant that I had
to take 10 minute exposures so that I could get the RGB data while M31 was
still reasonably high. The short colour exposures coupled with some slightly
hazy skies and gradually lower position means that there were some significant
gradients to deal with. I could not get as good a match as I would have
liked and there is some evidence in the top left corner of a join that I
just could not shift. There are also some differences at the lower right.
Moral of the story (stating the obvious) is to take longer exposures if
possible and try to get the best images with respect to position, light
pollution and sky conditions, or at least try to minimise the difference
between frames. It is easier to eliminate gradients that are unavoidable
if you have better data to work with. Processing was with Astroart for basic
calibration and RGB combining. The mosaic was compiled in Adobe Photoshop
with the colour and luminance done separately and then combining the finished
luminance and RGB images.
|
