Hamilton Amateur Astronomers
Maintained by Rob Roy
If you profess to be an amateur astronomer, you must have a map of the heavens as a guide. Even if you have a telescope that finds objects for you, you have to know enough to tell it what to look for.
A planisphere is one of the most useful tools for learning the constellations and the names of brighter stars. It usually consists of a pair of rotating disks that, when you hold it overhead and face in the correct direction, will show your entire sky view on a given date at a specific time.
Even if you know the night sky quite well, a planisphere is still useful answering for you such questions as: "At what hour will Orion be near the meridian (due south) in mid-November?" "What constellation is just rising at 3am on February 14?" "What months see the Big Dipper high overhead in the early evening?"
It's even fun to just play with one, comparing hourly changes with those from month to month. Phillips and Miller are two good planispheres. They are made for different latitudes, so make sure it roughly matches yours. Current magazines have charts of the sky for the first few hours of the evening, but don't expect to be able to go out at 3am in January with a January-issue sky chart.
A search for faint objects, such as most galaxies and nebulas, requires more detailed star charts. Popular astronomy books such as "NightWatch" or "The Backyard Astronomer's Guide", contain a selection of these, if not a full set, to whet your appetite and to get you started.
You really need a collection of maps covering the whole northern sky for the whole year- a star atlas. They come in several classes dependent mostly on the faintness of the stars shown. Atlases for beginners show stars to mag. 5 or 6 and deep-sky objects a few magnitudes fainter than that. The Messier list, brighter NGC objects, binary stars and variable stars are usually shown.
A few examples of these 10-12 page beginner atlases are: "The Cambridge Star Atlas", "The Mag 6 Star Atlas", "The Color Star Atlas" and "The Bright Star Atlas". Mag 6 has descriptions and useful information on the page opposite each chart.
The next step is to graduate to an intermediate atlas, Will Tirion's "Sky Atlas 2000.0" probably the finest. It shows over 43,000 stars down to mag. 8 and about 2500 deep-sky objects on 26 large charts. It is produced with black stars on white, white on black and full colour, all of which can be purchased with weather-proof lamination, if desired.
Serious advanced observers use the two-volume "Uranometria 2000.0", showing stars down to mag. 9.5 and thousands of deep-sky objects on 473 charts! Sets of "Astro Cards" are also available. These 3x5-inch cards usually show a single deep-sky object amongst the stars needed to fix its position. There are sets for the Messier objects, NGC objects, binary stars and targets for large telescopes.
Whatever map you use, you need to know exactly how it compares with your view of the sky. Your naked-eye view may not match the directions in your finderscope which in turn may not match those in your telescope.
Knowing your directions is most important. On star charts, north is up and east is left. A straight-through finderscope, refractor or Schmidt-Cassegrain has north down and east on the right side:- simply turn your chart upside-down. These same scopes, equipped with star diagonals have views that are upside-up but reversed left to right:- turn your chart over, hold it over a light and look from the back! If you can print your own computer-generated charts from a program such as "Earth Centered Universe", one axis can be reversed, matching any view:- a decided advantage.
Knowing your viewing size is also important. Using your finderscope, scout around to find the angle from one side to the other. Try Orion's belt or stars in the Big Dipper, for example, or you may already know the diameter of its field of view. Construct a circle of wire or on plastic to match the same view on your chart. Now, wandering over your star chart, you know what to expect to see in your finderscope. You can do the same with the widest-angle eyepiece for your telescope.
Observers use different plans of attack. Searches for complete sets of objects are common. The 110-object Messier list is usually the first quest, to be followed possibly by the Caldwell list or a galaxy-only list. Another approach is to pick a specific area, a constellation or a square on one of your charts, and try to find all of the objects therein.
None of this even begins to cover observing guides, handbooks, catalogues or almanacs, not to mention atlases of the Moon. There's an incredible wealth of observing information available. The truth is out there- find it and use it!
Rob Roy
Observing Director
Hamilton Amateur Astronomers
Maintained by Rob Roy
