Recommendations for Beginning Amateur Astronomers

 

 

Recommendations for Beginning Amateur Astronomers

 

Copyright (c) 1998, 1999, 2000 Jay Reynolds Freeman (freeman@netcom.com

  • Recent Revisions:
    • Near end -- Revised recommendations for the lazy.
      Expanded section on CyberScopes.

Amateur astronomers occasionally seek advice on telescope buying, learning the sky, observing skills, and so on. Here are some thoughts.

(My credentials? I do visual astronomy: I have logged about 13000 observations of over 5000 objects, and used some thirty telescopes and binoculars enough to know them well. I have made about ten optical surfaces to 16-inch diameter. My forte is deep-sky work: I am especially proud of logging the Sculptor Dwarf Galaxy (10x70 binocular), Maffei I and Einstein's Cross (Celestron 14), and Simeis 147 (6-inch Maksutov). My interests led to a physics PhD, studying the interstellar medium from a spacecraft: By training I am an astrophysicist, but I have amateur status in the visual -- my thesis work used extreme ultraviolet light.)

What to do First.

Written words do not replace experience. Join an astronomy club, go to observing sessions, try others' telescopes. You will learn a lot.

To find clubs, ask at science stores, museums, and planetariums. College physics or astronomy departments may know, though clubs aren't their line. The magazines Sky & Telescope and Astronomy publish annual directories of clubs, stores, observatories, and such. Find them on newsstands, or in a library -- or try their respective web pages, www.skypub.com and www.kalmbach.com.

Been to a club already? Honest? Okay, keep reading...

If you have a telescope, you might skip on to "What about observing skills?". Otherwise, here are some hints on telescope selection.

Hey! Just Tell Me What To Buy.

If you must be led by the nose, I have put specific recommendations in a postscript at the end. Just don't come crying when you find you would have made a better decision with more homework: I told you so!

Some Basic Questions.

Telescope buyers face bewildering, expensive choices. To deal with the confusion, ask yourself these questions.

 

  • How much effort will you put into learning the sky? If you know the constellations, and have practiced finding things by "star-hopping" -- using charts instead of dial-in or punch-in coordinates -- you will be able to use a telescope cheaper, smaller, lighter, and easier to set up than one using precise alignment or computer control to locate objects.

     

  • How much effort will you spend on your observing skills? Seeing fine detail in celestial objects, or just seeing faint ones at all, takes practice and special knowledge. Yet the rewards are great: An experienced observer may see things with a small telescope that a beginner will miss with one five times larger, even with objects and sky conditions that favor both telescopes equally.

     

  • How far must you lug your telescope to get to where you use it, by what means, and how much effort will you put up with? Differences in size and design make differences in portability: Any telescope you take out and use is better than one so heavy or cumbersome that it stays in the closet.

     

  • Are you into fancy technology for its own sake, even if not useful or cost effective? If so, fine -- me, too. But if not, take care technology fans don't sell you things you don't need.

     

  • Do you want to take photos or CCD images of celestial objects? That's expensive. Folks who do it (I don't) often take several telescopes and several years to be satisfied, and spend lots of money.

With these thoughts in mind, I can make some general comments.

Some Realities.

 

  • The most important determinant of telescope optical performance is the diameter of the beam of light it accepts -- its "clear aperture". More light shows fainter things, and less obviously, clear aperture affects image detail, via physical optics. Bigger telescopes produce sharper images, just because they are bigger. Clear aperture is so important that telescopes are usually labeled by it -- a six-inch instrument takes in a six-inch diameter beam of light, and so on. There are some qualifiers, though.

     

    • First, bad craftsmanship can make any telescope perform poorly. Yet it is not hard to make small telescope optics: Most companies usually turn out decent units, and if not, many manufacturers will often fix or replace a lemon, if you have wit to recognize one, and will to complain. (Many have neither; that's how some manufacturers make money!)

       

    • Second, different designs perform differently. Schmidt-Cassegrains, Newtonian reflectors, and refractors all have good and bad points. Folks who love telescopes, or sell them, will be eager to debate their merits, but variations in optical performance among telescopes of the same aperture and quality of optical work are relatively minor. They usually correspond to aperture changes of only 10 or 20 percent. Shabby optical work will increase that percentage enormously.

      There is one special case: For delicate planetary detail, a fine refractor may do 50 percent better than a fine example of any other common design.

       

    • Third, atmospheric turbulence ("seeing") keeps a telescope from showing detail, and sky brightness keeps it from showing faint objects. Poor seeing hits large telescopes harder than small ones. In poor seeing, there may be no reason to set up a big telescope, so if you always observe in such conditions, you may not want to buy one. Yet even in bright sky, a large telescope will show fainter stuff than a small one, and many of us have found dark-sky, stable-seeing sites not too far from home: From sites an hour from San Francisco Bay, sometimes I have to stare through the eyepiece of my Celestron 14 for several minutes before I can tell there is any air between me and what I am looking at.

       

    Notwithstanding these caveats, APERTURE WINS, and wins big. If you buy the finest 90 mm fluorite refractor in the world, be braced for a junior high school student to make a 6-inch Newtonian that blows it out of the water. The 6-inch I made at 13 puts my world-class 90 mm fluorite to shame, and not because I was a master optician at 13, but because six inches is bigger than 90 mm, hence intrinsically better.

     

  • Hundreds of deep-sky objects show well with two-inch aperture at low magnification: Medium sized binoculars -- 7x50 or 10x50, say ("7x50" means "magnifies 7 times, 50-mm aperture") make simple, highly portable, inexpensive beginner instruments. Do you have one? To use them well, learn the sky enough to find things with a hand-held instrument. Don't get one that gets too heavy to hold steady before you are done observing.

     

  • Speaking broadly:

     

    • The most optical performance per unit of clear aperture comes from modern, high-quality refractors -- which are outrageously expensive compared to other designs of the same aperture. Also, in sizes much above four-inch aperture, the tubes are usually long enough to make the whole instrument cumbersome and heavy.

       

    • The most optical performance per unit of portability comes from Schmidt-Cassegrain and Maksutov-Cassegrain designs -- but they are still pretty expensive.

      One qualifier: Their portability comes from short tubes, but for small apertures -- four inches or less -- portability of all types is dominated by clumsiness of the tripod, so the advantage of Schmidt-Cassegrains and Maksutov-Cassegrains diminishes.

       

    • The most optical performance per unit of cost comes from Newtonians -- particularly those with Dobson mountings. They are clumsier than Schmidt-Cassegrains and Maksutovs of the same aperture, but not nearly as clumsy as refractors.

    Let me regroup that information into three common questions:

     

    • What gives most optical performance for a given aperture?

      Usually, a high-quality refractor.

       

    • What gives most optical performance for a given car to carry it?

      Usually, a Schmidt-Cassegrain or Maksutov-Cassegrain.

       

    • What gives most optical performance for a given budget?

      Usually, a medium to large Dobson.

     

  • Though costly and cumbersome, small refractors are durable and hard to get out of whack. Good ones make decent beginner instruments, particularly for beginners with extra thumbs. A good small refractor makes it easy for an experienced observer to embarrass folks with giant Newtonians, who lack observing skills to exploit them. But BEWARE of mass-market junk refractors, advertised as high-power and sold in department stores.

     

  • Though equatorial mountings are very convenient, altazimuth ones tend to be cheaper, lighter, less clumsy, and more quickly set up. Yet to use one you must learn the sky enough to find things without dialing in coordinates. (Computer controlled altazimuth mountings allow use of celestial coordinates to find things, and may look them up in a database for you, but not all telescopes have them, and they are not always cheap.)

     

  • There's another way to look at this material. There are ecological niches for telescopes, corresponding to different uses and requirements. I know of seven:

     

    • Big Iron: This is the giant Dobson-mounted Newtonian, or humungeous Schmidt-Cassegrain, that fills your garage. To transport it requires a small trailer, pickup truck, or panel van, and setting it up calls for the concerted efforts of three used fullbacks and a circus elephant. The ladder to climb to the eyepiece is so tall you need supplemental oxygen to deter altitude sickness. This telescope is your galaxy-gazer and cluster-buster supreme, and if well made, then when the seeing is good it will show detail those condescending high-tech dweebs with their confounded itty-bitty apochromatic refractors can only dream about.

      My Big Iron is Harvey, a white Celestron 14 that stands six feet, three and a half inches tall on its Losmandy G-11 mounting. Believe it or not, Harvey fits into my Geo Metro with room for me and plenty of luggage, too.

      Buyers of Big Iron enjoy a diverse market. There are many manufacturers of Dobson-mounted Newtonians with apertures as much as a meter, there are amateur-type Newtonians with apertures up through at least 40 cm available on German equatorial mounts, and Celestron and Meade have Schmidt-Cassegrains of apertures 35 and 40 cm, respectively.

       

    • Largest Conveniently Portable Telescope: This is the most telescope that will fit in your regular vehicle without hiring a bulldozer to clean it out. What it is, depends on your vehicle -- with a ten-speed, or a subway train, you have a problem. An eight- to eleven-inch Schmidt-Cassegrain is just right for many; that is one reason these telescopes are popular.

      I have had several of these, over the last few cars. Once I built an eight-inch Dobson designed so the tube just barely fit across my back seat. I used it a lot till I bought a smaller car. For a while, my Largest Conveniently Portable Telescope was a Vixen 90 mm f/9 fluorite refractor on an altazimuth fork or a Great Polaris German equatorial, but now I use a six-inch f/10 Intes Maksutov on the Great Polaris. A faster Dobson than my 8-inch would do, with more performance for most purposes.

      There are several manufacturers each of 15 to 25 cm Dobson-mounted Newtonians, 12 to 25 cm Schmidt-Cassegrains and Maksutovs, and 9 to 13 cm refractors. Any of these will do for a Largest Conveniently Portable Telescope.

       

    • Public Star Party 'Scope: This is something portable, with the added provisos that it's nice to have a sidereal drive, so you won't have to re-point between viewers, and that it should not be so expensive you worry about kids and idiots. An SCT will do.

      I put the Intes or the 90 mm Vixen fluorite on the Great Polaris, but I set the tripod legs to maximum length, so the expensive optics are out of reach. So far, no one has slam-dunked a rock.

       

    • Quick Look 'Scope: The idea is to leave something set up in the entrance hall, or hidden under a stack of Sky & Tels in the car, all ready on a minute's notice if a truly close comet comes whizzing by, or if you are too lazy to assemble one of your real telescopes. Such an instrument can also double at nature watching or spying on the neighbors, which may be the same thing -- but don't tell your fellow astronomers, or you will lose observer points. Many of us have a spotting 'scope on a light tripod, or a 90 mm Maksutov on a heavy one.

      My current Quick Look 'Scope is Refractor Red, a 55 mm f/8 Vixen fluorite refractor on a light altazimuth mounting that has slow motions. It is indeed finished in day-glow red paint.

      Truly excellent telescopes in very small sizes are scarce, and few, if any, are in production. If you want a high-end Quick Look 'Scope, my advice is to wait until you know exactly what will be right for you, then keep an eye on the used market until it shows up.

       

    • Binocular: A binocular can do much of what a Quick Look 'Scope does. I have too many: For astronomy I use a 7x35 Tasco (from Sears, $29.95) that I keep in my car for birding (oops, lost observer points), a Swift Commodore Mark II 7x50 (out of production), which was one of the first binoculars I saw with BAK-4 prisms, and an Orion 10x50 and 14x70 with BAK-4 prisms and multicoated everything, up to but not including the case. At star parties I wander around with a binocular dangling from my neck. I tried two, but ran out of eyes.

      There are binoculars of every shape and kind, and describing how not to pick a bad one takes a whole separate article. Be careful, because there are lots of junk binoculars on the market.

       

    • High-Tech Conversation-Stopper: This is how you shame those grass-chewing hillbilly clodstompers whose giant cardboard Dobsons have tubes so big they echo. Odds are the seeing will never get good enough to demonstrate that a half meter shaving mirror will blow eighteen centimeters of optical perfection clean out of the water, and when they go on about faint galaxies, you can change the subject to diffraction rings and modulation transfer functions, and ask them to compare internal baffles and background sky brightness. Besides, your telescope has more knobs than all theirs put together, and it cost more than all theirs put together, too.

      The default High-Tech Conversation-Stopper these days is usually an apochromatic refractor, or something close. ("Apochromat" is a precise technical term; not all superb refractors are apochromats, and vice-versa.) If well made and well baffled, it will deliver outstanding performance for its size. Available sizes suffice for many amateurs who have recovered from aperture fever or not yet succumbed, or who have exhausted their supply of fullbacks and circus elephants to set up the Big Iron. Few other telescopes types qualify -- you're not allowed to have a Schiefspiegler unless you can spell it, and nobody wants a Yolo because people expect you to walk the doggie. Some Maksutovs make the grade, particularly Maksutov-Newtonians with tiny diagonal mirrors.

      My High-Tech Conversation-Stoppers are the 90 mm Vixen fluorite I mentioned earlier, and a 1987 model Astro-Physics 155 mm refractor I bought recently. The Vixen is too small to be really impressive, and is short on knobs, but I talk fast enough to make up the difference. The Astro-Physics is bigger, and does a vastly better job of inflating my ego, but it almost doesn't fit in my car.

      There are at least four manufacturers of first-rate refractors whose wares are regularly sold in the United States, where I get to see them, and several more elsewhere in the world. High-end Maksutovs in both Cassegrain and Newtonian configurations are available from several manufacturers. They are somewhat less expensive than refractors, hence show up in larger sizes.

       

    • CyberScope (suggested by Bill Arnett): With the processor power of a microwave oven and servomechanisms accurate enough to bring an object into the field of a medium-power eyepiece, a computer-controlled telescope declares to astronomers and computer types alike the owner's level of sophistication in both disciplines. Advanced versions log observations in your own digitally simulated handwriting, brew coffee to keep themselves awake, and buy off local raccoons with Oreos, all while you sit inside at your real computer, writing space-combat video games in graphically-enhanced modularized compiled Tiny BASIC for Windows 2000 NT. The battery truck is huge.

      CyberScopes do a decent job locating large numbers of objects from an internal database, and permit motorized tracking with a telescope lighter, less bulky, simpler to set up and align, and rather more expensive than if it were equatorially mounted. Low-quality mechanisms and sloppy construction often restrict their potential. Even so, those fond of technology may like them a lot, and folks with skill and equipment to program the control interface have a field day doing things most of us have never dreamed of.

      I do not presently own a CyberScope. That's because I write programs for a living, and too many of them. In my hobbies, I avoid anything suspected to contain electrons.

      Actually, I don't feel the need for one, because of personal history: I developed my star-hopping skills before CyberScopes became available, and I find myself good enough at it that a "go-to" interface wouldn't help much. I spend enough time looking at things I find, that it wouldn't go a lot faster even if I could locate new ones instantly. Star-hopping isn't hard to learn, and I expect most amateur astronomers would find use for the knack if they had it. Yet not everyone chooses or bothers to learn it, and most beginners want to find things to look at right away.

      In any case, prices of electronic aids for finding objects, both as accessories and as part of the original telescope, have been declining. The ease of use of such equipment, and its advantages for people who do not know the sky well, has probably gotten many folks going in the hobby, who would otherwise have been intimidated or frustrated by inability to find things to look at.

      Several manufacturers produce telescopes with computer-operated drive motors. They can find objects on the user's behalf. Many more produce digital setting circles (DSCs), both as part of complete telescopes and as add-on accessories, that tell where a telescope is pointed. They even work for altazimuth-mounted telescopes, including the ubiquitous Dobson-mounted Newtonians.

      At present, I can think of only two reasons to be cautious about purchasing such equipment. First, its cost is not always negligible, particularly if you are contemplating adding the capability to a telescope that didn't come with it. Second, the fancier stuff -- in particular, the computer-operated drives -- is not available on all the kinds of telescopes that you might want to buy.

 

What are common mistakes?

  • Do not buy a telescope at a drug store or department store. Such places are often full of outrageously priced junk. Trashy small refractors abound. I am not saying you cannot find good equipment at a decent price at such places, only that it will take skill, knowledge, and patience to separate the wheat -- if any -- from the chaff.

     

  • Do not buy a telescope advertised primarily on the basis of high magnification. The high magnifications may well be attainable, but are unlikely to be useful: The marketeers are trying to attract the ignorant and draw attention away from the shabby aspects of their merchandise.

     

  • Do not try to buy a telescope useful for both astronomical and terrestrial observations. These uses have different and conflicting requirements. It is easy for the unwary seeker of something that is supposed to do both, to end up with something that actually does neither.

    There are a few units that are okay for both, but they tend to be very expensive. If you really need both capabilities, you may well get more for your money to split your budget into two portions, and buy two separate telescopes.

     

  • Do not buy a spotting 'scope for astronomy. Spotting scopes are designed for looking horizontally, with an image that is upright and not mirror-reversed. The eyepiece position will likely require craning your neck when looking upward, and the extra optics to get the image straight will raise the price and degrade the view. Also, spotting 'scopes must be robust enough to haul around. That makes them heavier and costlier than astronomical telescopes the same size.

    The tripods generally used with spotting 'scopes often do not allow the telescope to point very far above the horizon. That is a serious obstruction to doing astronomy. Parents often buy a little telescope on a table-top tripod of this sort, for a child who wants to look at the stars, without realizing that it won't point high enough to see them.

    On the other hand, a spotting 'scope on a light tripod is often handy for quick looks at things. Just be sure you are willing to put up with its limitations before you buy one.

What about mountings?

 

A badly mounted telescope may jiggle too much, or move in jerks too big for finding things. Beginners often do not appreciate these problems, and many units advertised as first telescopes have mounts that are way too flimsy, particularly mass-market junk refractors.

Good mounts can be expensive. For equatorially mounted telescopes, a very rough rule of thumb is that a decent mounting will cost as much as the optical tube assembly. Good altazimuth mountings are generally less costly, but that does not mean cheap altazimuth mountings are good ones.

Carefully weigh the benefits of an equatorial mounting versus its added cost, weight, and bulk. Even without a sidereal drive, an equatorial mounting often makes it easier to find objects and track them across the sky, and it also helps figure out directions in the field of view. Yet if you mostly prefer to observe deep-sky objects at lower magnifications, these advantages may be minor.

A driven mounting, whether equatorial or altazimuth, also offers advantages. It helps when you are making precision observations at high magnification, or when you want to step away from the eyepiece to consult your charts or make notes, and it is invaluable for showing things to long lines of people at a star party.

Among altazimuth mountings, the style invented by John Dobson has special merits. Sturdy construction from materials that damp vibration well makes a good observing platform. Slippery plastic -- like DuPont's "Teflon" -- in the bearings lets you track stars by hand, without electrical or mechanical slow motions. Simplicity permits inexpensive Dobson mountings that are solid and durable. Unfortunately, some commercial manufacturers of Dobson-mounted Newtonians have cut too many corners, and produced units that are too flimsy.

What about accessories?

I have already said most of what you need to know about accessories, which is that APERTURE WINS. If you are budgeting a telescope, and eyepieces, finders, and such account for most of your funds, think more on what you plan to do -- it might be better to get a bigger telescope instead of fancy accessories. A 10-inch telescope with a hand magnifier as eyepiece will give a better view of most objects than an 8-inch with the world's best eyepieces. Why? Because APERTURE WINS.

Yet if you are up against limits of telescope portability, or have lots of money, or like technology, go ahead and buy fancy accessories. I won't tell, provided you remember that APERTURE WINS.

In any case, I will mention some plain-vanilla accessories that you might want to have, and maybe a few chocolate ones, too:

 

  • Eyepieces. A few good ones is better than many bad ones. You need a low-power, wide-field eyepiece, to find things and to see big, faint, diffuse objects. It might have magnification equal to one fifth the telescope clear aperture, in millimeters. On my f/11 Celestron 14, the low-power eyepiece has a 55 mm focal length, and is mounted in a two-inch barrel, so the front lens -- which sets field diameter -- can be as large as possible. (In smaller telescopes, internal baffles may mean no light gets to the edge of a two-inch wide eyepiece; if so, don't bother paying for one.) On my f/5 8-inch Dobson, I use a 20 mm Erfle eyepiece, which doesn't need a two-inch barrel.

    The next power you will likely reach for is medium to medium high, to see details. Such an eyepiece might give magnification roughly equal to telescope clear aperture, in millimeters. On my C-14 I use a 12 mm eyepiece, and on my 8-inch Dobson, a 4 mm. The objects you look at with this power probably won't be very wide, so for economy, you might not want a super-wide-field type.

    Your next choices will depend on what you like to look at. If you are not sure, hold off buying more eyepieces till you find out.

    "Fast" f-numbers, typical in Dobson-mounted Newtonians, need fancy, expensive eyepieces to give good views, because the steeply converging light cones of these instruments are difficult for an eyepiece to cope with, particularly away from the center of the field. Slow instruments can use simpler eyepiece designs. A "Catch-22" of amateur astronomy is that cheap telescopes (fast Dobsons) need expensive eyepieces, but expensive telescopes (most refractors and Schmidt-Cassegrains, with slow f numbers) can use cheap eyepieces.

    "Zoom" eyepieces change focal length at the twist of a knurled ring, but most of the ones around are not very good. Recently, however, Vixen and Tele Vue have released serviceable units, whose range of focal lengths -- 8-24 mm -- neatly spans most of the range that many of us use for deep-sky observation. Visibility of faint features often varies dramatically with magnification, and is sometimes maximized only over a very narrow range, so a good zoom eyepiece may be a valuable addition to the deep-sky observer's kit. Yet do try one out before you buy, for they are not cheap.

    Barlow lenses, also called telextenders, multiply the focal length of a telescope: It used to be that they generally worked well only with telescopes with large f-numbers, where they were not needed -- another "Catch-22". There are now Barlow lenses that work with fast telescopes, where they are needed, but I urge a try-before-you-buy approach to selecting one.

    For over fifteen years I used an eyepiece set bought in 1980. It had no fancy designs, just a 55 mm Plossl, 32, 20, and 12.4 mm Erfles, and 7 and 4 mm Orthoscopics. The 55 and 32 mm eyepieces were in 2-inch barrels, the others in 1.25 inch barrels. All were good quality -- the 55 and 32 mm were from University Optics, and the others were Meade Research-Grade. All worked reasonably, even at f/5, and the 68-degree apparent field of the Erfles was enough so I was not tempted by wider-field types. Besides, a big Erfle is already so heavy that I must rebalance the telescope to use one. I did use the 4 mm eyepiece on the C-14, but only rarely.

    In mid 1996 I bought some more. I found that decent Plossls are comparable to Orthoscopics. I got some Vixen "Lanthanum" eyepieces, with built-in Barlow lenses to give 20 mm eye relief, even at such short focal lengths as 2.5 mm. Even without glasses, long eye relief makes viewing more relaxed: I don't worry about bumping the eyepiece. It also helps with public viewing: I focus with glasses on, and tell folks to leave theirs on and not refocus.

    A year or so later, I started becoming more particular about eyepieces for viewing objects with lots of fine detail. I eventually bought several Brandons -- a design labeled "Orthoscopic" but which resembles a Plossl -- for that purpose. They are rather expensive, but I was willing to pay for increased performance.

    Note what high-tech eyepieces can and cannot do. The best give wider fields, with fewer eyepiece aberrations near the edges, than older types. The improvement is most noticeable at fast f numbers. If that matters to you, you might want some. But eyepieces are not aperture stretchers. They cannot increase image detail beyond the theoretical limit for the aperture, or increase the number of photons that make it to your eye. If you think otherwise, you are making the same mistake as the clueless beginner who buys a drug-store refractor because the box shouts "Magnifies 675 Times!!!". The best an eyepiece can do is not make things worse. A simple eyepiece, with good coatings and well-polished lenses, will show all the on-axis detail a telescope has, and absorb and scatter almost no light. That's what counts most for astronomical work.

    In 1980, I bought several Ramsden eyepieces -- an old, simple, design -- for some ten dollars each. I use them at star parties without telling. They have only four air/glass surfaces, so simple coatings give good throughput, and there are few chances for bad polish to scatter light and ruin contrast. The field of view is narrow, but on axis, at slow f numbers, they give up nothing to new designs; images are superb.

     

  • Finders. What kind of finder you get depends on how you use it. If you look mostly at fine details in bright objects, you might buy a big finder, so what you look at will be visible in it, too. But if you push your telescope to its faint-object limits, you would need a finder as big as the main telescope. You might then consider one that shows stars exactly as faint as on your charts. It helps a lot in identifying stuff in the finder, if every star you see is charted, and vice-versa. Once the right pattern of stars is in the finder, you can put the crosshair where the object lies, even if it is too faint to see.

    In dark sky, the 10x40 finder on my C-14 shows stars to beyond magnitude 9.5, which is a good match for my big charts. The 7x35 on my 6-inch Maksutov does almost as well. In suburbia, the 5x24 finder on my 8-inch Dobson goes to about magnitude 6.5, which would be the naked-eye limit in darker conditions, thus matches many naked-eye star atlases.

    Unit-power finders, like the Telrad, let you view the sky with both eyes, and see a pattern of light where your telescope is pointing. A cardboard and tape peep sight may work as well, and will be much cheaper, and any magnifying finder in which you face where the finder is pointing, can be used with both eyes open -- just let your brain fuse the images from both eyes. I tried a unit-power finder (Orion's) on my 90 mm refractor, but found it inferior to the original 6x30 finder.

    My opinion on unit-power finders is in the minority. I suggest you practice with both magnifying and unit-power types, then decide which is for you.

     

  • Charts. Preferences vary greatly. What I find useful, in order from simple to complicated, is more or less the following:

     

    • A simple planisphere, preferably a plastic one that won't sog out with dew and that may survive being sat upon. It's a fast way to find out whether a particular object is up before I go observing, or to check how long before it is well-placed.

       

    • A "pocket atlas". I am particularly fond of Ridpath and Tirion's The Night Sky, from Running Press in Philadelphia, PA. It is about three by five inches and half an inch thick, and out of print. Write Running Press and complain.

       

    • A small "table atlas", bound as a book that will lie reasonably flat, with stars to the naked-eye limit, and many deep-sky objects to boot. I happen to use an old Norton's Star Atlas; there are others.

       

    • A "deep atlas", like Uranometria 2000, the AAVSO atlas, or the new Millennium Star Atlas, with stellar magnitude limit of 9 or more and a vast number of objects. What's important here is to have plenty of charted stars in every finder field.

       

    • A planetarium computer program (Bill Arnett reminded me). If you are a beginning astronomer, I do not suggest you rush out and buy a computer, but if you already own one, bear in mind that there are programs that turn your console into a window onto the simulated heavens, with features to find, display, and identify things. I happen to have the rather old Voyager 1.2 for my even older Macintosh II; there are plenty more, both for Macs and for the world descended from MS-DOS.

      Some folks run such a program on a laptop, at the telescope. Please put red cellophane over the screen, if you do.

    I have little use for the popular oversize-format charts with lesser magnitude limits, like 7.5 to 8.5; they don't show enough stars to be useful with my finders, and are too cumbersome. The plastic-laminated versions make good place mats, though. Everyone should use the box of a Dobson as a picnic table at least once.

     

  • red flashlight, so you can read your charts and notes without ruining your night vision. Kinds with a glowing red diode instead of a bulb are particularly good. If other observers scream and throw things, your light is probably too bright.

     

  • logbook. This item is not for everyone. I like to record my observations, even if I merely note that I saw a certain object with a certain telescope and magnification. Logbooks make fun reading when it is cold or cloudy, and often there is reason to look up something later. Besides, if you quote often from your logbook, you can make people think you are an active observer years after you quit.

What about observing skills?

Even some experienced amateur astronomers think seeing things comes free and easy, with no more effort than opening your eyes: But as current popular slang so evocatively articulates,

 

NOT!!

Vision is an acquired skill. You must learn it, you must practice, and you must keep learning new things, and practicing them, too.

Buying a big telescope to see better is like buying a big pot to cook better, or a big computer to program better. It might help, but cooking and programming depend more on knowledge and experience than on hardware. So does visual astronomy. People with garages full of telescopes (I can't close the door to mine) are victims of materialism, marketeering, and hyperbole. Practice is cheaper, and works better. As I said before, an experienced observer may see things with a small telescope that a beginner will miss with one five times larger.

Canadian amateur astronomer Gary Seronik has said that telescopes are like musical instruments. It takes time to learn to play them well, and even an accomplished musician cannot necessarily make beautiful music with a new or unfamiliar instrument right away. And it certainly doesn't make sense to buy a bigger piano or guitar with the hope of thereby making better music.

What skills may you hope to cultivate? What techniques should you practice? Not all have names, but here are a few, in what I think is order of importance; what matters most comes first.

 

  • Patience. It can take a long time to see everything in a field, even if you know exactly what you are looking for. Some of the skills discussed below are not completely under voluntary control, like eye motions, and seeing and transparency may vary rapidly. It may be a while till everything adds up right.

     

  • Persistence. Eyes, telescope, and sky vary from night to night.

I am not kidding by putting patience and persistence first. There is a lot of stuff in my logbook that I did not see during the first five seconds, or the first five nights, or even the first five years. If you give up, you won't see a thing.

 

  • Dark adaptation. Avoid bright lights before observing: It takes your eyes hours to reach their full power of seeing faint objects. It may help to sit for several minutes with your eyes closed before attempting a particularly difficult observation.

     

  • Averted vision. The part of your retina that sees detail best, sees low light worst. Look "off to the side" to find lumps in the dark.

    Many observers use averted vision on faint objects, but forget it for bright ones. Detecting something doesn't mean you've seen all of it. Don't let the dazzle of a galaxy's lens make you miss spiral arms that go beyond the field edge. How about increasing magnification, and using averted vision to seek more detail in the paler, larger, image?

    Averted vision helps with double stars, when one star is much fainter than the other, even if the faint star is bright enough not to need averted vision if it were by itself. I don't know why.

     

  • Stray light avoidance. Even when it's dark, background glow interferes with detecting faint objects. Keep it out of your telescope and out of your eyes. Try eye patches, and eye cups for eyepieces.

    My first view of the Sculptor Dwarf Galaxy was with my jacket collar pulled up over my binocular eyepieces. I looked like a cross between the Headless Horseman and the Guns of Navaronne, but I saw the galaxy.

     

  • Changing magnification. Old sources about observing faint objects sometimes suggest only such low magnifications as 0.15 to 0.20 times the telescope aperture in millimeters. Yet I sometimes find best detection of faint galaxies at magnifications of 0.7 to 1.0 times telescope aperture in millimeters. For bright objects in poor seeing, many people back off the magnification till seeing jitter is not visible, but doing so foregoes glimpses of fine detail when things are momentarily steady.

    If you don't change magnifications, how can you be sure you are using the best one?

     

  • Focusing critically. Particularly at higher magnification, precise focus is important to see all the detail. In poor seeing, it can take a long time to get the focus set right, but it's worth doing.

     

  • Moving the telescope. The eye sometimes detects motion, or changing levels of brightness, more easily than static images. Jiggle the telescope, or move it back and forth, to make an object "pop out", perhaps only in the moment just after the motion stops. Sometimes you can detect the edge of a large object only because the intensity of what you thought was "background" changed as you moved the telescope, and brought it into the field. Try all this while using averted vision.

     

  • Not moving the telescope. The eye sometimes adds up photons over many seconds; if you can hold your eye still for a long time, faint things may appear. Try it with averted vision.

     

  • Respiratory and circulatory health. If you smoke, try taking a break before and during observing -- carbon monoxide from incomplete combustion interferes with the ability of the blood to transport oxygen.

     

  • Hyperventilation. Don't risk fainting, but a long series of deep breaths, or at least, a conscious effort not to hold your breath, may better oxygenate your blood and so improve your ability to detect faint objects.

Clear sky, and enjoy your telescope.

 

 

                                                -- Jay Freeman
                                                   freeman@netcom.com

PS: Specific Recommendations For The Lazy.

If you are too lazy to do your homework, for shame! Oh, all right, here are some recommendations which may help if you are buying in the United States. Since you forfeit any claim to making an informed decision, I will not explain or justify them.

 

  • If you have a binocular, take it out and use it.

     

  • If you have no binocular, get one. Buy a Tasco model 2001, which has 35 mm diameter front lenses and magnifies seven times. It sold in Sears for $29.95 (US), last time I looked. It is second rate, but good value. Try it in the store: Make sure it doesn't rattle, and that you can get usable images from it. Do not buy the similar "zoom" unit.

     

  • To learn the constellations, buy The Stars: A New Way to See Them, by H. A. Rey, Houghton Mifflin, paperback, ISBN 0395248302. Last time I checked, amazon.com had it for $9.56.

     

  • For a more general star atlas and observing guide, buy Norton's Star Atlas and Reference Handbook, 19th edition, edited by Ian Ridpath, Addison-Wesley, paperback, ISBN 0582356555. Amazon.com recently had it for $23.96.

     

  • Start reading at least one of the two popular astronomy magazines, Sky & Telescope and Astronomy. I prefer the former. In the United States, you will probably find both on most large newsstands.

If you simply must have a telescope right away...

 

  • Do not buy a refractor. Not having done homework means you cannot tell wheat from chaff: Junk refractors abound.

     

  • If you can't afford to spend five hundred dollars, forget about buying a telescope, or at least, forget about buying a new one.

     

  • If your budget is five hundred dollars, and you choose to spend that much without knowing what you are doing, buy a six-inch Dobson-mounted Newtonian telescope, model XT6, from Orion, recently listed at $369. (US), plus shipping. Reserve the rest of the budget for additional eyepieces and other accessories.

    The Orion Dobson-mounted Newtonians are not first-rate, but these telescopes are good values. The company has a web site, atwww.telescope.com.

     

  • If your budget is several thousand dollars, and you choose to spend that much without knowing what you are doing, there are some more choices.

     

    • For deep-sky observing, set aside at least $500 for eyepieces, and buy from Obsession Telescopes,http://www.globaldialog.com/~obsessiontscp/OBHP.html, a 15- to 20-inch truss-tube Dobson-mounted Newtonian, with lots of accessories. These are superb instruments for faint fuzzies. Expect it to be bigger than you expected.

       

    • To satisfy a yen for gadgetry, set aside at least $500 for eyepieces, and get a Celestron 8-inch Schmidt-Cassegrain in the computer-controlled "Ultima 2000" model line. Celestron's main web site, http://www.celestron.com, lists dealers. This model is a compact, general-purpose telescope that weighs less than its competitors, with enough whizzy features to pass for "high-tech". Expect it to be less perfect than you expected.

      Cheaper Celestron 8-inch Schmidt-Cassegrains work just about as well, but without the whiz.

       

    • If you want uncompromisingly exquisite optics, then I will give you special dispensation to buy a refractor. Set aside several thousand dollars for a mount and eyepieces, then get in touch with Astro-Physics, at http://www.astro-physics.com, and line up to buy an optical tube assembly for one of their refractors. Many lunar and planetary observers prefer high-end refractors, and this is one of the best. Expect to wait longer than you expected.

    I say again, you will make a better decision and be happier with your purchases, if you join a club and do some homework first. I repeat: You will make a better decision and be happier with your purchases, if you join a club and do some homework first. Good luck!

 

 

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