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Author: admin | 29.09.2014 | Category: Ringing In The Ears Causes

Here's a quick guide to help you make sense of all the types of telescope models available today. Many (arguably most) good starter scopes cost $400 or more, though some superb choices are available for under $250.
The telescope you want has two essentials: high-quality optics and a steady, smoothly working mount. The most important characteristic of a telescope is its aperture — the diameter of its light-gathering lens or mirror, often called the objective. Avoid telescopes that are advertised by their magnification — especially implausibly high powers like 600?. The three basic telescope designs use different optics to achieve the same result: making distant objects look bigger and brighter than they appear to your eye. The objective's focal length (F or FL) is the key to determining the telescope's magnification ("power"). On some mounts the scope swings left and right, up and down, just as it would on a photo tripod; these are known as altitude-azimuth (or simply alt-az) mounts.
Some telescopes come with small motors to move them around the sky with the push of a keypad button. But Go To scopes aren't for everyone — the setup process may be confusing if you don't know how to find the bright alignment stars in the sky. This scope was bought with the following rule in mind: The scope that gets used regularly is always a better scope than the one that rarely or never gets used. Our nearest celestial neighbor is a familiar face - and a fantastically rich target for a clear night.
But by knowing just a few basics, described here, you'll be able to choose the one that's right for your observing interests, lifestyle, and budget.
Armed with these few basics, you'll have a good idea what to look for (and what to avoid) when scouring the marketplace for your new scope. But read this article first, so you'll understand the terminology and what type of telescope will be best for you.
And all other things being equal, big scopes show more and are easier to use than small ones, as we'll see below.

Look for the telescope's specifications near its focuser, at the front of the tube, or on the box. But a good small scope can still show you plenty — especially if you live far from city lights. For most purposes, a telescope's maximum useful magnification is 50 times its aperture in inches (or twice its aperture in millimeters) . See the text for links to animations that show how light passes through the optics of each design.
For a given aperture, these are generally the least expensive type, but you'll need to adjust the optical alignment periodically — especially if you bump it around a lot.Watch an animation of light passing through a reflector.
This is simply the objective's focal length divided by that of the eyepiece, which you'll find on its barrel. Many telescopes come conveniently packaged with tripods or mounts, though the tubes of smaller scopes often just have a mounting block that allows them to be attached to a standard photo tripod with a single screw. Many reflectors come on an elegantly simple wooden platform, known as a Dobsonian, that's a variation of the alt-az mount. In the more advanced models of this type, often called "Go To" telescopes, a small computer is built into the hand control.
And lower-priced Go To models come with smaller apertures than similarly priced, entry-level scopes that have no electronics. With a little care in selecting the right type of telescope for you, you'll be ready for a lifetime of exploring the night sky! Kelly Beatty, S&T's Senior Editor, joined the staff of Sky Publishing in 1974 and specializes in planetary science and space exploration. For astrophotography, the aperture is less important since you can make up for it with a long exposure, but you need a really good equatorial mount. I faced this factor last year when I decided to buy a first telescope for my 8-year old granddaughter. Whether you’re tracking down Apollo landing sites or observing the marks of lunar history, this collection will guide your journey to the Moon.
But don't overlook portability and convenience — the best scope for you is the one you'll actually use.

The aperture's diameter (D) will be expressed either in millimeters or, less commonly, in inches (1 inch equals 25.4 mm). For example, you can spot dozens of galaxies beyond our own Milky Way through a scope with an aperture of 80 mm (3.1 inches) from a dark location. A more involved mechanism, designed to track the motion of the stars by turning on a single axis, is termed an equatorial mount. Once you've entered the current date, time, and your location, the scope can point itself to, and track, thousands of celestial objects. I ended up buying her a 76mm tabletop Dobsonian scope because this was one that she could carry in and out of the house herself and, when set on the back yard table, had the eyepiece at an appropriate height for her. As a rule of thumb, your telescope should have at least 2.8 inches (70 mm) aperture — and preferably more. But you'd probably need a 6- or 8-inch telescope like the one shown at right to see those same galaxies from a typical suburban backyard.
Most types of telescopes come supplied with one or two eyepieces; you change the magnification by switching eyepieces with different focal lengths.
An equatorial mount (right) can track celestial objects by turning just one axis and can be more easily motorized — but to work properly it must be aligned with Polaris, the North Star.
These tend to be larger and heavier than alt-az designs; to use an equatorial mount properly you'll also need to align it to Polaris, the North Star. Some "Go To"s let you choose a guided tour of the best celestial showpieces, complete with a digital readout describing what's known about each object. And regardless of how bright or dark your skies are, the view through a telescope with plenty of aperture is more spectacular than the view of the same object through a smaller scope.

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