Getting Started in Astronomy: Part 3

Stargazing and telescopes go hand in hand.

Seronik-2011 MKSP

Waiting for twilight to fade with telescopes at the ready is a familiar ritual for backyard astronomers. Courtesy Gary Seronik

Astronomy = Telescope

A telescope really opens up the universe for detailed exploration. Even a modest instrument can show incredible detail on the Moon’s surface, Saturn’s beautiful rings, Jupiter’s subtle cloud belts and countless star clusters, nebulas and galaxies. With a good telescope, a lifetime’s worth of sky sights awaits.

Seronik-Moon detail

The Moon’s battered surface is a spectacular sight in just about any telescope. Courtesy Gary Seronik

Telescopes are available in a bewildering array of shapes and sizes, and selecting one can be daunting. But one consideration overrides all others: When it comes to seeing fine lunar and planetary detail or glimpsing distant, faint galaxies, bigger is definitely better. More than any other single factor, the telescope’s aperture (the size of its main light-gathering optical element) determines what the instrument can deliver. Simply put, in the realm of telescopes, aperture is king.

But what about magnification? Isn’t a 500× telescope better than a 100× instrument? The short answer is no. Magnification is essentially a meaningless specification. Here’s why. A telescope’s magnification is set by the eyepiece — the part through which you actually look. All astronomical telescopes use interchangeable eyepieces that allow you to select the magnification. As a result, any telescope can be made to magnify to any power depending on which eyepiece you choose. But how good the views are at a given magnification is based on the telescope’s aperture. For example, 200× in a 2-inch telescope produces views that are quite dim and blurry, while the same magnification in a larger telescope can yield bright, crisp images. Bottom line: Don’t buy a telescope on the basis of its magnification. Any telescope promoted that way is very likely of poor quality and targeted at the impulse shopper.

Seronik-Eyepieces

MAGNIFICATION MATH
Eyepieces like these are crucial for powering your scope. To determine your telescope’s magnification, simply divide the focal length of the telescope by the focal length of the eyepiece. For example, a 24-millimetre eyepiece used in a telescope with a focal length of 1,000 millimetres will yield 42× (1,000 ÷ 24). A 10-millimetre eyepiece in the same telescope will produce 100×. Courtesy Gary Seronik

Telescopes come in several optical varieties, each one having its supporters and detractors. A refractor telescope uses a lens to gather light. The so-called apochromatic refractor has more complex lenses that generally provide the best image quality, though perfectly acceptable images can be seen in an ordinary “achromatic” refractor. Quality at a premium price is the refractor’s calling card. The Newtonian reflector telescope uses a precisely curved mirror to gather light. Such instruments offer excellent bang for the buck, especially in the simple Dobsonian configuration. The biggest telescopes in the hands of recreational astronomers are reflectors. Compound telescopes that utilize both lenses and mirrors are another popular variety of astronomical instrument. The Schmidt-Cassegrain telescope (SCT) and the Maksutov are the most common. They offer a lot of aperture in a compact package, a combination that makes them particularly appealing to amateur astronomers who must travel to observe.

Each type of telescope comes in a wide range of apertures and prices and can be carried on different styles of mount. An altazimuth mount moves the telescope in simple up-down and left-right motions, like a super-beefy camera tripod. A Dobsonian telescope utilizes a specific kind of altazimuth setup. In an equatorial mount, one of the axes is tilted toward the north celestial pole, which simplifies the motion needed to follow sky targets. Either style can be motorized and equipped with computerized controls for GoTo pointing and tracking.

Seronik-Refractor and Dobsonian

TELESCOPE MATTERS
Refractors, like the 66-millimetre instrument shown on the left, gather light with a high-quality lens and offer sharp views of the Moon and planets. The Dobsonian reflector (right) features a 300-millimetre mirror to pull in lots of light. Courtesy Gary Seronik

Detailed descriptions of all the available telescope and mount configurations are beyond the scope of this article, and as with so many things, there is no one “best” choice. A telescope is a major purchase, so it pays to do your homework. If you can, visit a telescope store or attend a star party and kick the tires in person. Don’t overlook practical considerations, such as size and weight. Try to imagine setting up and using the telescope night after night or at a remote location. Is it too big or heavy to handle? Find out what accessories are included, and set aside some of your budget to purchase extra eyepieces. A little research in advance will save you a lot of grief later. A great place to start is with a copy of Terence Dickinson and Alan Dyer’s excellent book, The Backyard Astronomer’s Guide. It’s chock full of detailed telescope information and practical hands-on advice.

Finally, if you’ve decided the time is right to buy your own telescope, resist the urge to pop down to the local mall or megastore. These places often sell instruments that are little more than telescope-shaped junk. For something that will bring you lasting enjoyment, visit a store that specializes in optical equipment or purchase online from a reputable telescope dealer.

Click here to go to Part 4 of our Getting Started series.

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