The Atmosphere

When a deep blue, breezy afternoon turns to a dark and clear night, with stars twinkling brilliantly, we have a night of high transparency. The dark sky and high contrast afford ideal conditions for viewing galaxies, nebulae, and faint stars. Unfortunately the other side of the coin — air turbulence — is often present. On such nights the seeing is often poor. A small telescope shows twinkling stars jumping about playfully, but large apertures average out the motions, giving us steady blobs. Many novice observers are unaware that transparency and good seeing usually avoid one another. The hazy summer doldrums often produce the best seeing and are excellent for revealing double stars and planetary details.

Another factor we must all confront is encroaching light pollution combined with atmospheric haze from industrial pollution. While everyone should pitch in to make our planet cleaner, the immediate answer for an observer is to pack the car and travel to a remote site. It is no coincidence that very portable telescopes, big and small, are becoming more popular, and that star parties are popping up at dark-sky sites all over the country.