Most people rich enough to buy telescopes live in industrialized countries, and most people in the industrialized world live in cities and suburbs. That means that light pollution is a major factor for most backyard astronomers.
Light pollution takes two forms: glare from lights that are directly visible — usually streetlights or neighbors’ “security lights” — and skyglow, the diffuse glow scattered down to your eyes from thousands or millions of surrounding lights. Glare is quite obvious, and it’s often fairly easy to avoid by politely asking your neighbors to dim their lights, erecting shields to block streetlights, or observing from a nearby park. Skyglow is subtler but also much harder to escape; it extends well over 100 miles from a major city and dozens of miles from a minor city.
Skyglow has no effect at all on the appearance of the Moon and planets, which are overwhelmingly bright. But it greatly reduces the number of stars visible both through a telescope and to the unaided eye, and it makes faint deep-sky objects (star clusters, nebulae, and galaxies) much harder to see.
I live in Cambridge, Massachusetts, less than five miles from the center of Greater Boston, a metropolis of four to eight million people. Between the years 2000 and 2002 I attempted to observe all of the Messier objects (the 109 best-known deep-sky objects) through three different instruments both from my local city park and from the inner suburbs. These are representative of the instruments used by and conditions experienced by most American stargazers. Many aspiring stargazers have found my descriptions helpful in knowing what they should expect when they set out to do deep-sky observing.
I summarized my nearly complete set of observations in an article in the April 2002 issue of Sky & Telescope magazine — an article that no doubt contributed to my being hired as an S&T editor a year and a half later.
The observations were done with three instruments: two telescopes and a pair of binoculars, which I will abbreviate throughout as follows:
|178mm:||Starmaster 7-inch f/5.4 Oak Classic Dob|
|70mm:||Televue Ranger 70-mm f/6.9 refractor|
|7×35:||Nikon 7×35 binoculars|
I did most of the observations with a single eyepiece: the Vixen Lanthanum 8-24mm zoom, yielding 20X-60X on the 70-mm refractor and 40X-120X on the 178-mm Dob. I also used a 30-mm Celestron Ultima for wide-field work on the refractor, and various wide-field 2-inch eyepieces on the Dob. In some cases, I might have gotten somewhat better views using higher powers than those provided by the zoom, but I chose to restrict myself for the sake of simplicity.
I tried a Lumicon UHC narrowband filter (also sometimes called a nebula filter) on all of the Messier nebulas. The filtered view was often clearer and/or more detailed than the unfiltered view, most notably so for M8, M20, and M97.