The purchaser of an astronomical telescope quickly discovers that there are several additional items, not usually supplied with new (or used) telescopes, that he or she needs to enjoy amateur astronomy. This little article is intended to briefly explore the most common and useful of these.

If you built your telescope yourself, or somehow acquired one without any mount, Celestron, Apogee, Tele Vue, Meade, Questar, and Losmandy sell mounts separately. Bogen and Gitzo are good sources for professional photo tripods and heads.

Serving the same purpose as a finder scope, but without magnification, are red dot sights like the popular Telrad. These project a red circle or dot on a glass, like a gun sight, and are very easy to aim at a target in the night sky, as long as it is visible to the naked eye. They usually mount by simply sticking them to the telescope tube, and they can be used alongside a conventional finder scope.

In addition, star charts usually have a planisphere on the front cover. A planisphere is a handy rotating representation of the night sky placed behind a large oval window that represents your field of view (assuming a flat horizon). You rotate it to set it for the date and time you are observing, and it shows you the major visible stars and constellations, and where they are in the night sky. Planispheres are also available separately, for a few dollars, at most book stores.

Pelican offers the versatile "Mity Lite Mini System" flashlight. This comes as a kit with a replacement halogen bulb, two AAA alkaline batteries, and both clear and red lenses, all in a compact plastic box. It is completely waterproof, and also makes an excellent travel flashlight. (Always take along a small, high quality flashlight when you travel; it will come in handy, and can literally be a lifesaver in an emergency.) The price is quite reasonable, about that of the red LED flashlights sold by the major mail order telescope dealers. The latter also work fine, and batteries will last almost forever in them. In addition, Celestron offers a disposable Red Astro Lite flashlight for about half the price of a Pelican Mini system, or a red LED flashlight.

Binoculars for hand held astronomy should be standard size, sharp, and from 6 to 10 power. Avoid compact binoculars, they are not bright enough. They should have an exit pupil (the light pencil you see when you hold your binoculars at arms length and look through the eyepieces) of from 5 to 7 millimeters. This insures that sufficient light reaches your eyes to let you see dim objects.

To determine the exit pupil, simply divide the diameter of the front (objective) lens by the magnification. For example, 7x35 binoculars have a magnifying power of 7x, and 35mm front objectives. Thus, the exit pupil is 5mm (35/7=5). 6x30, 7x35, 8x40, and 10x50 binoculars all have 5mm exit pupils. 7x50, 8x56, and 9x63 binoculars all have 7mm exit pupils. All of these are standard size binoculars, and all of these will serve the amateur astronomer well.

Good binoculars are available from many manufacturers, at many price points. It is best to avoid cheap department store brands (like Jason, and Tasco), although almost any binocular will help in a pinch. Most of the standard size binoculars from the major Japanese camera companies are quite good. These include Nikon, Minolta, Pentax, and Fujinon. Zeiss, and of course Leica (Leitz), from Germany, are the very best. Some telescope companies like Orion and Celestron also offer good binoculars. Celestron has an excellent line of binoculars that I regard as the best value in the field. My favorite binoculars for hand held astronomy are the Celestron Ultima series 8x56 and 9x63 models.

For a lot more information about binoculars, I strongly advise purchasing the excellent little $4.95 book "How to Choose Binoculars" by Alan Hale (President of Celestron). You'd think it would just be a pitch for Celestron binoculars, but you'd be wrong; it is an easy to understand guide to binoculars in general, and includes specifications from all of the top manufacturers.

The most common filter, and the only one virtually everybody needs, is the neutral density (ND), or "moon" filter. This is usually the kind of filter that screws into your oculars. Since your telescope gathers over a hundred times more light than the unaided human eye, looking at the brightly lit moon is a blinding experience--akin to staring into a halogen flashlight. The neutral density filter is a neutral gray filter that merely reduces the total amount of light, so that you can look at the moon without discomfort. It is like sunglasses for your ocular. Celestron, Meade, Tiffen, and others offer moon filters at reasonable prices.

Another common eyepiece filter is the polarizer. It serves much the same purpose as the (cheaper) moon filter, cutting glare and reducing the total amount of light reaching your eye, and is available from the same sources.

A useful filter for city dwellers is the light pollution reduction filter (LPR). These can be the type that screw into oculars, or the type that fit the visual back of certain telescopes. There are broad band and narrow spectrum LPR filters. What they attempt to do is cut down on the sky glow from certain types (frequencies) of outdoor lighting common in cities. These filters are quite a bit more expensive than the moon filter mentioned above, but worth it if you must view from a light polluted site. They are offered by Celestron, Meade, Lumicon, and others.

Another useful filter, and one which MUST (for safety) cover the entire front of your telescope, is the solar filter. These visually opaque filters can be made of either glass or mylar (both work well). They allow you to safely look at the sun, the only star you will ever be able to examine closely. You will be able to see sunspots, and the granulation of the surface of the sun (which looks kind of like an orange to me). Because of their size, solar filters are relatively expensive. Thousand Oaks Optical and Celestron, among others, offer good solar filters at fair prices.

As the stickers plastered all over your new telescope warned, NEVER attempt to look at the sun without a solar filter which covers the entire front of your telescope. The sun is not something to toy with; it is a mainline star undergoing nuclear fusion. Your telescope gathers over a hundred times more light than the unaided human eye, and if you look through it when it is pointed at the sun, you will be instantly and permanently blinded. The light and heat of the sun will melt the inside of your finder scope, if it is not covered while your telescope is pointed at the sun. Ultimately, the build up of heat from the sun will melt the inside of your telescope. Eyepiece solar filters are not sold by reputable manufacturers because they are not safe!

There are also colored filters, often sold in sets, much like those available for camera lenses, which screw into your eyepieces. Various colors are supposed to enhance your view of certain planets, etc. I have tried these filter sets, but not found them to be very useful. Celestron, Meade, Tiffen, and others offer colored filters.

Distributors like Lumicon offer specialized filters for exotic purposes, which cut or pass very specific frequencies of light. These tend to be expensive filters, but they are necessary for observing certain phenomena otherwise invisible to the human eye. If you get into those areas, you will learn what filters you require.