effects of periodic tracking errors. The total exposure time was ten minutes for each
colour filter:
M97, NGC3587. The Owl nebula. This planetary nebula lies at a distance of 2600 light years
in the constellation of Ursa Major. PHD guiding was used with a 10 inch, f/4.8 reflector.
Sub frames five minutes long were captured. The exposure time for H-alpha was sixty
minutes, and the exposure time for Olll was ninety minutes. These data were then combined
with the colour data using RGB filters with exposure times of twenty minutes for each
filter:
