Choose the Right Telescope

Ever been interested in space and the night sky? Well, these steps will start you off on a great adventure.

Steps

  1. The diameter of the objective lens or mirror is the most important number describing a telescope. Larger diameter lenses or mirrors allow higher resolution (ability to separate closely spaced objects) and will gather more light from faint astronomical objects. They also cost more. A good size for a first telescope is roughly four inches (100mm). Bigger tends to be considerably more expensive and more inconvenient. Bigger works better, of course, though not shockingly so.
  2. Magnification is relatively unimportant and is often hyped in advertising claims for inexpensive telescopes. In astronomy, the purpose of a telescope is mostly to collect light from faint objects, not to magnify them. Most visual observing is done between 50 and 200 power.
  3. Too much magnification just gives you a useless blur. A good rule of thumb to determine the maximum usable magnification is to multiply the diameter of the objective in millimeters by 2.5 (which means that the typical department store 60mm scope is only usable to 150x). In actual practice, on nights of extremely unusual atmospheric stability, you -may- be able to use a somewhat higher power, but don't count on it.
  4. The better eyepieces have larger "eye relief," which represents how close you have to get your eye to the eyepiece to observer clearly. If the eye relief is too small you will have to bring your eye very close to the eyepiece, and it will be all but impossible to observe for more than a few seconds at a time.
  5. Look for a steady mounting, an unstable or shaky mounting will ruin your observing experience. In general, the more massive the mount looks, the better it performs. When in doubt, spend more on a mount.
  6. Join an astronomy club and learn to use someone else's telescope before buying your own.
  7. Start with a pair of binoculars and learn to find things in the sky before buying a telescope. (Or, if you just want to see pretty objects, get a GoTo mount.)
  8. Don't expect a small telescope to show the same images that you see in astronomy textbooks, which are usually long time exposures and may have been taken by much larger professional grade telescopes. No telescope practical for most individuals to own will show significant color in nebulae to the naked eye, although bigger ones will show shape well, and many can reveal color through time-exposure photographs.



Tips

  • Consider getting a telescope with a "GoTo" mount such as Meade's Autostar or Celestron's NexStar -- it will find things for you to look at and prevent you from endless searching. Even with these "GoTo" scopes, you still have to be careful in leveling the tripod and picking the right bright stars to perform alignment on. You typically have to choose two or three bright stars to align on so that the telescope knows where on Earth it is situated. The cheaper systems should then place each object of interest within the field of view of the widest angle eyepiece; it can be centered with the scope's controls. If the system is consistently inaccurate the problem may well be that it needs to be calibrated to the slack in the scope's gears (which is perfectly normal). Meade calls this "training" the drive. The manufacturer should be happy to explain over the phone how to do this.
  • The free Android phone application "Google Sky Map" uses the compass, GPS and orientation sensor to show a map of the part of the sky it is held to face, and is great for finding stars for purposes including initial alignment of a GoTo mount.
  • Don't buy a $200 eyepiece to get a higher power, instead, spend it on a better scope.
  • Try to get a reflector telescope for best viewing -- a refractor is fine as well. Reflector telescopes are much cheaper for a given objective size, but to perform at their best they require regular collimation--making sure the internal mirrors point perfectly straight down the tube. There are special eyepieces (called "Cheshire" eyepieces) that are inexpensive and make collimation much easier.
  • Contact your local planetarium if you have further questions about buying a telescope. They will be happy to guide you to local and mail-order dealers who are reputable.
  • For best results, look through a telescope in a dark place. In a city, you're not going to see much. There are special eyepiece filters available to help reduce light pollution from streetlights, but they are not dramatically effective and are expensive.

Warnings

  • Never look at the sun with a telescope or binoculars. You may blind or severely damage your vision for the rest of your life by doing so.

Things You'll Need

  • Telescope
  • accessories (eyepieces, filters, etc.)

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