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AMATEUR ASTRONOMY FOR BEGINNERS: AN ONLINE GUIDE
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PART I: A LITTLE BACKGROUND INFORMATION
Choosing the right telescope can be just as important as learning the constellations. There are so many choices and price ranges on the market today that it can seem a complicated landscape of equipment to navigate. With such a variety of equipment built to specialize in different areas of astronomy it is safe to say that there is no such thing as an ultimate one telescope that does all. But you don’t have to break the bank to get a decent scope that will last you a lifetime. At the same time you don’t want to spend hard earned cash on something made cheaply that wont last but a few years before it heads to the junk yard. All to often this last scenario happens to the uninformed novice and it completely turns them off to the hobby of astronomy… permanently. I’m often reminded of the advice a very good friend of mine once gave. “The best telescope is the one you use the most.”
Many times a person’s first encounter with a real telescope is in a department store. Usually around holidays like Christmas, retail stores pack their shelves with telescopes offering huge magnifications at a relatively cheap price. Getting hooked on this sort of advertizing is one of the first mistakes beginners often make. There is a term in astronomy called useful magnification. In other words magnification is only useful at magnifying details up to a certain point. After that any more magnification only serves to magnify a fuzzy blob making it a larger fuzzy blob. The average small backyard telescope typically has a maximum useful magnification of anywhere between 200X-350X, give or take. Anything more than that is generally made useless by a combination of factors such as the size of the scope and seeing conditions.
The resolution of or the amount of detail you see in an object through a telescope is ultimately governed by the size of the telescopes primary optic (its largest mirror or lens). To gain resolution you would have to increase the size of your telescopes primary. This is why professional astronomers build ever larger telescopes. Thus it’s not the magnification of a given eyepiece that is important but rather the size of the diameter of the telescope’s primary optic.
REFLECTOR VS REFRACTOR
There are various reasons for choosing a reflector over a refractor or vice versa but its not a huge issue when starting out. If you graduate to the intermediate or advanced levels of amateur astronomy, like the rest of us amateurs you will probably end up having a collection of scopes too. Typically its important that the aperture of any reflector be a minimum of 4.5 inches in diameter. Anything smaller and you might as well get a refractor or binoculars. As for refractors a bare minimum diameter is 60mm. The recommended size for a small refractor is between 80mm and 90mm. Anything less than 60mm will be disappointing. Keep in mind that the bare minimum for binoculars is a 10X50, where 60 represents the diameter of the binoculars primary lens(50mm). A 60mm refractor is essentially a “monocular”.
When it comes to prices, the reflector always wins over a refractor. Its cheaper to make a larger reflector than it is a refractor of the same size. With reflectors you get a bigger bang for your buck. The larger reflector gives you an advantage when it comes to faint light sources from deep space objects. Remember that size does matter when it comes to teasing out details and collecting photons of light from galaxies far, far away. Reflectors are also not subject to chromatic aberration like refractors. The lens of a refractor has difficulty focusing the violet region of the visible light spectrum at the same focal point as the rest of the spectrum. This produces a purplish coma around bright objects. There are filters for refractors, called fringe filters, that can block the violet part of the spectrum and thus block the purplish coma. However, refractors do have something to offer over reflectors. When it comes to viewing bright planets and the moon they are awesome. For some reason the details on planets and lunar features seem sharper as seen through refractors. Refractors are also well suited to astrophotography.
EQUATORIAL MOUNTS VS ALT-AZIMUTH
The telescope mount can be one of the big hang-ups when it comes to learning how to use a telescope, especially with equatorial mounts.
The easiest mount to use is the simple alt-azimuth, where the alt or altitude axle moves the telescope up or down, and the azimuth axle moves the telescope left or right. No complex alignment to the celestial pole is required but you must move the telescope in both altitude and azimuth to track an object across the sky. Dobsonian telescopes and some higher end “goto” scopes use this type of mount.
There are advantages to having an equatorial mount over the simpler alt-azimuth. The most obvious being that you are able properly orient your telescope relative to the earth’s spin axis and your latitude location on the globe. This allows you to track an object with one axis alone. However, the equatorial mount must always be aligned to the celestial pole and unless your telescope is in a permanent location you will have to do this once before every time you observe. The issue with low end budget scopes and equatorial mounts is that they usually don’t come with a motor to automatically track for you. Some of them still have a gear in place so you can purchase the motor separately. Equatorial mounts are generally better for higher end “goto” scopes with heftier mounts used for astrophotography or long periods of intense visual study of an object. This doesn't mean you shouldn’t get one on a budget scope. If you learn how to use an equatorial mount in the beginning, you’ll be ready to handle it when it comes to purchasing a higher end model for advanced purposes.
EYEPIECE BARREL SIZE
There are two standard eyepiece barrel sizes on the market today. These are 1.25” and 2”. Older scopes came with a smaller .965” barrel size which is all but nonexistent nowadays. Make sure that the scope you choose accepts either the 1.25” or 2” sized eyepiece barrel or both.
Consider the weight of the telescope you buy. Remember that you will have to carry it outside every time you want to observe. Larger scopes are heavier and more cumbersome to transport. I can guarantee from personal experience, that there will come a time when the thought of carrying all that weight outside will be the deciding factor on when and if you observe on a given night at all. If you are worried that a telescope is a little on the heavy side, try looking for its weight in the dealer’s specifications section. Duplicate the scope’s weight by filling a large bag or suitcase with an equal amount of weight.
I recommend seeking out and paying a little more for a well known brand. This ensures that you wont have to deal with an odd ball scope that virtually no one has ever heard of and who’s manufacturer provides no support in the form of upgrades, accessories, or help with problems. Meade, Orion, Celestron, and Zumell are just a few of the brand names that amateur astronomers purchase products from.
THE PRACTICLE GUIDE TO BUYING A TELESCOPE
B. 700X Magnification
C. Reflector VS Refractor
D. Equatorial Mounts VS ALT-Azimuth
E. Eyepiece Barrel Size
G. Brand Names
A. The Budget Class
1. The Tabletop Telescope
B. The Dobsonian Class
C. The GOTO Class