Light pollution is the glow to the sky caused by outdoor lighting such as Sodium street lights or Halogen lights. The light from these sources reflects off of particles in the sky and can ruin your phtoographs. If you are a city dweller, you should try and scout out a good place to take the scope in the country. Light Pollution appears as a glow on your photos, typically orange in colour (caused by the sodium street lights).

When outside, you should try and keep away from any sources of light and switch off your motion detecting halogen light if you have one. The light from these can spoil your dark vision. This is the term used to describe your vision when your eyes adjust to the darkness, becoming more sensitive to light (dark adaptation).

You will probably require some sort of light source however, to save tripping on your equipment, etc. As your eyes are least sensitive to red light, you should get a red bulb for your torch or just put some thick red film over the front. This will conserve your dark vision and save you fumbling about in the dark.