Imaging in an Urban Area

For those of you who live in a major urban neighborhood amongst Bortle 9 skies, you'll understand the issues with setting up and executing an observing session in this type of neighborhood, especially if it's your backyard.  There usually are unnecessary lights everywhere - your neighbor’s house lights, nearby street lamps and especially the sky glow from distant lights in the city's commercial centers or the downtown area itself.

In addition to the light pollution, you probably have several obstructions to work around.  For me, I am not able to view the eastern half of the sky from my backyard because my house (and several others) is in the way.  As for the western half of the sky that I do have access to, there are large trees and telephone and power lines that are issues I have to work around.  The good news is, that even with all these problems, I can still get good image data to work with.  But it does take advanced planning and patience and a good light pollution filter at your disposal to use.  Here’s what I’ve learned so far…

First, you need to have a plan for where and how you setup your equipment.  This means an examination of and a comparison of the different location options in your backyard.  A lot of this work you may need to do during the day as well as at night.  During the day, it’s easier to determine where all the physical obstructions to the sky you'll need to take into account.  It’s also easier to understand where Polaris or Sigma Octantis is in reference to your home site since you’ll need to consistently perform an accurate polar alignment for your mount (unless you’re going to go manual).  Once this is decided, you’ll understand what amount of sky is actually available to you.  

You will need to make an appraisal of what the proposed site looks like at night.  There you’ll notice how much stray light from your neighbors’ home and/or locally from the street you’ll need to contend with.  A major tip  - if you’re on good terms with your neighbors, talk to them about extinguishing their outside lights when you’re observing or imaging.  They may be very happy to do so especially if you offer to share views of the major planets or the moon with them when these objects are viewable.  This opens a window to begin educating your neighbors about the night sky, especially when something special like a lunar eclipse happens or a stray comet wanders into the neighborhood.  Objects like M31, M13 or M42 are usually bright enough to see in small to moderate sized telescopes or binoculars in very light polluted skies;  most people are not even aware these fine objects even exist.

The last lesson?  When viewing or imaging, your target needs to be reasonably high in the sky to get the best views.  This means at least 35 to 40 degrees above the horizon.  If the target is much lower, the light pollution we all suffer with becomes a problem even with good filters.  I’ve also gained a lot more respect for using monochrome cameras with only a light pollution or narrowband Ha filter.  The images will be monochrome, but you can get a lot of detail, especially from bright nebulas such as M42, the Orion Nebula or NGC 281, the Pacman Nebula.  This image of IC 434 was taken with an Ha filter on my QHY 294M camera from my backyard.