Sky Brightness

The single most important factor in deep-sky observing is light pollution. Its worst effect is on dim, extended objects of just the sort we're considering. A dark sky matters even more than telescope size; a small instrument in the country will show faint nebulae and galaxies better than a large telescope in a city.

That being said, even if you live in a badly light-polluted area you can take pleasure in what can be seen through the skyglow. New York City observer Jenny Worsnopp has examined nearly the entire Messier catalog from her Manhattan rooftop. Cambridge, Massachusetts, amateur Tony Flanders did the same from a city park. Just remember not to blame yourself or your telescope for what may seem like mediocre results. Rather, make a note to bring your telescope along on country getaways.

The higher in the sky you look, the darker the sky will be. Plan your deep-sky observing projects accordingly. Also, light pollution tends to improve a bit after 11 or midnight as some outdoor lights get turned off.

Keep an eye on the daytime sky. The deeper and cleaner the blue is in the afternoon, the cleaner and darker the air will be at night.

Moonlight, of course, is nature's own light pollution. When moonlight is in the sky, plan on sticking to bright targets.