Choosing the Best Star Atlasesby Robert Bruce Thompson, Barbara Fritchman Thompson
Despite the proliferation of computerized go-to telescopes and planetarium software for notebook computers and PDAs, printed star atlases remain extremely useful. Many astronomers, for example, use star atlases to plan their observing sessions because they prefer the "big picture" of a printed atlas to the constraints of a relatively small notebook or PDA screen. Many also use printed charts during observing sessions, preferring their familiarity and reliability. (You'll never have to cut short an observing session because the battery in your printed atlas dies.)
There are numerous star atlases to choose from, and those atlases vary greatly in level of detail, scale, physical size, price, and other important considerations. Which atlas or atlases are best for your needs depends on numerous factors, including:
- The aperture of your scope
- The darkness of your observing site
- The types of objects you observe
- The limiting stellar magnitude of the atlas
- The number, type, and limiting magnitude of deep-sky objects (DSOs) included
- Dew resistance
For example, a star atlas that is ideal for someone who observes bright star clusters from an urban location with a 3.5" refractor is poorly suited for someone who observes dim galaxies from a dark rural site with a 20" Dobsonian reflector, and vice versa.
Like many astronomers, we have both large and small instruments and observe from both urban and rural sites, so one star atlas is insufficient for our needs. The following sections describe the atlases we use, and our reasons for choosing them.
Mag 6 Star Atlases
Mag 6 atlases, also called "naked-eye" star atlases, chart stars down to magnitude 6.5 or so. No amateur astronomer should be without a Mag 6 atlas. They're useful for impromptu naked-eye or binocular observing sessions, and for times when you simply don't feel like hauling out the "serious" charts.
Mag 6 atlases show only a few hundred of the brightest deep-sky objects, including (usually) all of the Messier Objects and the brightest non-Messier NGC objects, such as the Double Cluster, as well as prominent double stars. Mag 6 atlases use a small image scale, typically mapping the entire night sky on a dozen or so small charts. This small scale limits the number of objects that can be shown and the amount of label detail for each.