Thinking of buying a telescope? Building a lifelong interest in the stargazing requires more than just a telescope. Please consider the following before you invest hundreds of dollars.
1) The diameter of the main mirror or lens is everything. The bigger the opening, the sharper and brighter the object. More diameter will allow you to see more detail in Saturn’s rings, or spots on Jupiter. More diameter means brighter images, thus allowing you see faint nebulae and distant galaxies. For serious stargazing, a 6” diameter (6” is about 15 cm or 150 mm) is about the minimum that will make you happy. An 8” is better (8” is about 20 cm or 200 mm). Some amateur telescopes get as large as 30 inches in diameter.
If you do not wish to invest in such an expensive telescope, and choose to purchase one with a smaller diameter, such as the very popular and inexpensive 60 mm and 80 mm telescopes sold in many toy stores and department stores, your successful viewing may be confined to the moon, the planets, and a few other objects.
There has been recent growth in smaller apochromatic refractors. These smaller diameter telescopes use a minimum of 3 lenses to make the image as sharp as possible. They are very expensive for their diameter. Because their images are so sharp, they are of particular interest to astrophotographers, who often take hundreds of digital photographs of a single object in a single night, and use computer software to average the photos and extract the maximum detail from them.
There is often an inverse relationship between size and frequency of use. If a telescope is smaller, it is easier to set up and use. And, the easier it is to use, the greater the likelyhood you will use it. If a 10 year old buys a huge telescope, they will not be able to set it up and use it without help from Mom or Dad. It will probabily only get used a few times a year. If they buy one they can set up themselves, they will probabily get it out much more often.
The best bargin, by far, is the telescope you build yourself. There is a whole subset of stargazing devoted to building telescopes. Many beginners buy a premade mirror and assemble the telescope around it. You can build an excellent 12" telescope for less than $1,000, if you have ordinary woodworking skills and a few tools.
2) Power, or magnification, is over rated. Theoretically, the maximum useful magnification of a telescope is a function of the telescope’s diameter. The rule of thumb is 50X to 60X for every inch of diameter. (In metric, this is about 20X per centimeter, or 200X per millimeter).
From a practical standpoint, usable power is often far less than theoretical power. Air pollution, moisture in the air, heat rising from nearby buildings, lakes, parking lots, etc. all contribute to poor viewing and make high-power views unusable.
On the other hand, you do not need much magnification to see many wonderful things. Most of the planets are quite beautiful at magnifications around 50X to 100X. In this range, you can see Saturn’s rings, Jupiter’s moons, and Venus’s crescent. If you are looking for galaxies or nebula, they are large and almost always look better at low magnification. Comets are very large, and need very low power wide angle views to find and see them.
3) Stability is extremely important. If a telescope trembles and shakes, it will be nearly impossible to locate objects. Focusing can become a nightmare. Each time you touch the focusing knob and turn it slightly, a poorly mounted scope will shake and vibrate. You will not be able to tell if things are in focus until the shaking stops. If this takes several seconds, you can spend literally minutes trying to focus. By then the object has moved out of your field of view, and you must start all over.
All telescopes shake. But the better ones only shake for a second or two when bumped. Judging the stability of a telescope is difficult without actually setting it up and using it. If you can try one out, great. But if you cannot, do some on-line searching and see what others have to say.
Shake can also be affected by the placement of the scope. Wind, soft soil, tilted ground, etc. all contribute. Some of these can be improved, others cannot.
For the most part, stability increases with price. For serious stargazers, the telescope mount alone can cost several thousand dollars. If a telescope with mount costs less than $100, I can guarantee it will shake. Above $100, some telescopes shake more than others. When you buy your telescope, discuss the return policy in case you are unhappy with its performance. If at all possible, take it home and try it out. If you cannot take it home, ask to try it at the store. When looking through it at high magnification, give the eyepiece a gentle nudge and see how long it takes to settle down.
4) Set aside some of your budget for books and computer software. Too many people buy telescopes and don’t use them because they don’t know what to point them at. To point a telescope, you need to know where things are in the sky. Books are great for learning the constellations. I highly recommend The Stars by H.A.Rey (he wrote the Curious George series). It is available in most libraries. Even better, buy the paperback for roughly $10 and keep it as a lifetime reference. In my opinion, it is one of the best constellation books in print. I know more stargazers who learned their constellations from this book than all of the other books combined.
Once you can find the constellations, then you need specific information about what to look at. I am a great fan of computer software. It lets you know what is in the sky RIGHT NOW! It tells you which way to look, and gives a great deal of information on each object. It will show you which planets are visible, when various objects rise and set, and help you plan out your viewing session.
If you can bring a laptop outside with you, I know of no better way of learning the sky than holding the laptop above your head with the computer screen exactly matching the real sky. If you have a desktop computer, print out the section of the sky you are interested in and hold the printout above your head. It works!
If you are using a Macintosh, I like the program called Voyager, by Carina Software. I also like the program Starry Night, which comes in several versions, ranging from about $60 to $200, depending on your needs. For a Windows computer, The Sky is powerful, expensive, and nice. Starry Night is also available. There are many others, each of which has its fans.
If you are good at surfing the internet, there are many shareware and freeware programs that do similar things.
5) Find and join a local group of stargazers. These groups are some of the friendliest folks I know. Many stargazers will offer hours of free advice. Most of them have owned several telescopes, and will be glad to make recommendations.
6) Visit a local planetarium. In the Ann Arbor area, there are several planetariums that offer shows on stargazing. These include the planetarium at the University of Michigan Exhibit Museum, the planetarium at Cranbrook, the Longway Planetarium in Flint, the Toledo Planetarium, the Hurst Planetarium in Jackson, and others. (I am afraid that the Argus Planetarium is only open to school groups.)
7) Make a stargazing friend. It gets very cold and lonely when observing the night sky. Some people relish the quiet, and send hours peering through their eyepieces. Others love to join clubs and go out in groups of 2, 3, or more, strollling from telescope to telescope during the night. But what will really keep you going is talking about what you are doing with someone else who is interested. A stargazing friend can be someone who views with you, or someone you talk to at work, school, by phone, or on the internet. A friend will help keep your interest fresh and new.
8) Subscribe to an astronomy magazine. The two best magazines are Sky and Telescope and Astronomy. They will keep you up to date on all sorts of interesting things. Sky and Telescope tends to be more technical. Professional astronomers often contribute articles. Astronomy likes pictures, and claims to be the most beautiful astronomy magazine published. Both are widely available on news stands and in libraries.
This article, of necessity, is brief. For those who are serious about stargazing, there is a wealth of information available in the book stores, in libraries, and on line. Take advantage of this. Owning and using a telescope can lead to a lifetime of pleasure.