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CN Report: Starting Off Right in Astronomy Pt. 1


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starting out right

Starting Off Right in Astronomy: Part 1
Tom Trusock 10/08


This one's for all the newbies out there who are interested in looking up at the stars. It's intended to be a basic introduction into choosing and using a telescope – y'all more advanced amateurs can just skip it.

There must be something fundamental about astronomy. I swear, I don't think I've ever met anyone who had an aversion to talking about looking at the night sky or thinking about what's up there. But for some reason, many people just don't make the jump to observing themselves. I've got some sneaking suspicions about why that is. I've been worried that many amateurs – especially some of the more gear oriented ones like you'll see on line – are unintentionally biased towards the high end of the spectrum when it comes to talking about gear. That can get a little – uh – awkward for someone who is looking to ask a basic question.

And it seems like more and more people are asking for advice these days. With that in mind, lets get started.

So ya wanna be an amateur astronomer? Great! It’s a wonderful hobby – full of rewarding and relaxing moments – it’s one that you can stick with through a lifetime.

There's a couple different ways to approach the hobby. Some folks are gear heads tried and true. They're easy to recognize. They've always got something new; an eyepiece, telescope, or some sort of new fangled accessory. Odds are, they've got one of the more sophisticated setups on the field, but (and here's the kicker) they may or may not do much observing with it. These folks like the toys. They like seeing the differences in performance first hand, and they probably lie collecting things too. The second type – well, we'll call them the purists. They care less about the gear and more about the observing. These are the folks who have a limited amount of gear, but focus on their observing.

I know a guy – we'll call him “Bob”. Bob is something of a purist. Bob cares more about observing the night sky than the tools one uses to do that with. Bob's out every clear night with his binoculars and his 8” telescope, and his copy of Nortons (that's falling to pieces). Bob is in direct contrast to Albert. Albert is the gear head primeval. Seems like I can't ever talk to Albert without him picking up some new piece of gear. Last week it was a telescope, yesterday an eyepiece. It's not uncommon that Al often does not have stuff long enough to actually observe with it.

Al's a computer guy, and everything is goto. If his batteries failed, he'd probably be in a spot of trouble. Ask him which galaxies he viewed last night and he can probably rip off a list of 30. He can tell you which telescopes and eyepieces give the most awe inspiring views on common targets, but ask him to locate M3, and he'll be lost. Bob on the other hand has seen more with his 10x50 binoculars than most of us could see with the Hale. Computers don't dominate his life – in fact, the only thing he has that uses batteries is his flashlight. And he's thinking about buying one of those shaker models. If this were travel - Bob, you see, is more concerned with the view. Al, on the other hand, really likes the cars.

Which is the right way to do astronomy? Both! And probably neither too. This is a hobby, when it comes down to it, the most important thing is to do it however you enjoy it. Have fun. If you want to get into the physics of optics – feel free. If you want to observe a life list of 10,000 objects, more power to ya. And if you just want to poke out under the stars with a set of binoculars or a telescope on occasion ala virtual tourist – even more power to ya.

To get started in this hobby, I recommend a decent pair of binoculars. We could argue gear for an eternity, but I'll make it simple and recommend you use what you've got lying around the house to start. You'll need some charts, and some ideas what to look at. There's lots of good books and resources out there. I recommend Steve Coe's What's Up, and my own Small Wonders articles here on CN. I also recommend a magazine like Astronomy or Sky and Telescope. Both of these have monthly observing columns that will present you with a choice of targets.

Binos are a great way to start. They really open up the skies, and they are something even the most accomplished visual observer likes to have on hand for those quick peeks. If you don't have a set, I recommend you concentrate on looking at 8x42's (first number is magnification, the second number is the aperture – how much light they gather) or 10x50's. I don't really recommend you go any with any smaller aperture (not as much light gathering) or higher magnification (too hard to hold steady). I'd say a budget of around $100 - $200 would be plenty – heck, there are even good deals to be had well below that – but you'll need to be picky. Later on, I'll give you some tips on how to check if those binos are worth your money or not, but lets save that for part II.

At some point you'll probably want a telescope – it just seems to be a natural progression. More light gathering, more flexibility – yeah they're a little less portable, but every thing's a trade off. So - How do you choose? Well, first off, lets take a look at the common designs on the market today.

There’s three main types of telescopes out there, the refractor, the reflector and the compound telescope, to help you figure out what’s best for you, I’ll give a little explanation of each and outline some of the advantages and disadvantages. Now you vets be a little patient with me, as I simplify things for the beginners out there. This is going to be somewhat like high school – yah, it may not be exactly correct but we’re still teaching the Bohr model – if you know what I mean…

Refractors - One for the purist

Refractors come in every size, color and pricepoint.

The refracting telescope is what most people think of when they think of a telescope. This design uses lenses to gather light and is quite popular in the hobby today – at least in smaller sizes.

Refractors are a low maintenance design - you don’t typically have to worry about much with these, just take them out and use them. They do have some of their own caveats and pitfalls though – the two biggest being that they need something to put it on – a mount, and they can – inch for inch – be the most expensive design on the market.

Most refractors fall into one of three categories: Achromatic refractors, apochromatic refractors and ones that lie somewhere in the middle.

An achromatic refractor is one that is corrected for two different wavelengths of light. In practical terms, this means that you'll see some false color in the image. Bright targets will be graced with a purple or yellow/green highlight. In spite of this, achromatic refractors up to about six inches in size are quite popular with amateurs today, largely because they are fairly inexpensive, and provide some very very nice views. Probably the most common type of achromatic refractor on the market today is the Fraunhoffer doublet refractor. This utilizes two distinct elements, one made of flint glass and one made of crown glass to help reduce that chromatic aberration (false color).

Apochromatic refractors are very popular with both visual observers and imagers (but a much harder hit on the pocketbook). Apochromatic telescopes have better color correction than achromatic telescopes. Ironically, the definition of achromatic means without color – since that’s the case, maybe we’d be best off thinking as apochromatic as “really, really without color, and we mean it this time!” While there is a technical definition of an apochromat – based partly on the number of wavelengths it can bring to a common focus, this is a term we’ll reserve for the best refractors on the market. Typically, apochromats are made with two or more elements, typically one made of ED (extra dispersion) glass. When coupled with the correct mate(s) this results in a color free system. Top notch apochromatic refractors can easily cost $2,000 and up just for a 3" telescope alone!  And don’t forget, you’ll also have to provide a mount for these guys.

What then, of the "third" type of refractor?

Over the past few years, refractors have become very popular telescopes, and we’ve seen costs begin to come down on them – the question you might want to ask at this point is: Why?

It’s not that the premium apochromatic refractors have been overpriced - not really. There’s a lot that goes into a telescope to ensure it’s the best possible performer it can be. The tolerances are tight – we’re talking wavelengths of light in terms of tolerances here, and quality control is a huge part of the manufacturers cost. There’s also a question of the cost of the raw materials and the time the manufacturer spends on an item. A lens that spends more time on a polishing machine and requires more human input naturally costs more than one that doesn’t. There are other factors that go into this as well - its simple economics.

But apochromatic telescopes sell, and there are a lot of companies that are bringing to market decent quality telescopes at a fraction of the price of some really high end gear. So what do you sacrifice with these? Typically color correction and corrections for some types of aberrations (the image isn't as sharp and pinpointy). You can also count on lower QC as well. They also tend to use less expensive materials – some of the less exotic glasses are quite a bit cheaper and while they offer decent performance it’s not quite up to the level of their more expensive brethren.  You'll also find that there most likely isn't the same amount of attention paid to selecting the glass to make sure of it's quality, and there's typically less time spent figuring and polishing the lenses as well.  You'll also find that the mechanicals (tube, focuser, etc) these manufacturers offer is a step below the truly top notch companies.

You'll find that the third type is symbolized by the "inexpensive" 80-102+mm apochromat – many of these scopes don’t quite offer the color correction their more expensive brethren do – in fact by strict definitions, many would probably not even qualify as apos. And yet these guys have a great following – largely because their price makes them affordable to a wide section of the marketplace and because they really can deliver some fantastic views.

The Newtonian Reflector – Go Deep!


Probably the most common telescope on the market today is the Newtonian reflector on a Dobsonian mount. Without question, these guys offer the best “bang for the buck”. There's a saying out there – Aperture rules. And all things being equal (figure, cool down, etc) that's 100% correct.

And this is where aperture walks in.

Good Newtonian reflectors gathers light using a parabolic mirror.  (Run away from any that offer spherical mirrors.)   Unlike most refractors, they need to be collimated. In this sense, it's maybe a little more fiddly than a refractor, but the process is still pretty easy to figure out and the gain in the views is really worthwhile.

Newtonians on Dobsonian mounts (we'll just call them dobs from here on out) have a few disadvantages – as I've already mentioned, they do require collimation; that is their optics do need to be aligned. The mirrors are what's called “First Surface” mirrors. That means the reflective material is on the front of the glass, not the back of the glass. The upshot is that it's not protected by the glass. It will decay and in a few years (anywhere from 10-20) you'll probably have to start thinking about getting that mirror recoated. Because of the nature of the parabolic curve used to reflect light, newts do tend to show an aberration called coma as you move away from the center of the field (we say as you move "off-axis"). Coma is an optical aberration that turns stars into comets. The good news most folks typically don't notice it in these common beginner scopes, and if you go beyond them, there are solutions out there to drastically reduce if not eliminate coma in the system.


Truss dobsonians break down into smaller packages
than their solid tube counterparts. This helps
with transportation.


And one more drawback all that aperture can be heavy to carry if you've got to constantly lug it up and down the stairs every time you want to view.

On the upside, if you want to see detail in deep sky objects – this is what you want.

Newt's are for the visual observers, a club of which I count myself a member. Unfortunately, I sometimes have the distinct feeling that we may be something of a dying breed - but that's a topic for another article.

The Compound Telescope – One for the Gadget Lovers

And then finally, there's this third category – these guys are a mixture of the previous two in that they use both lenses and mirrors to gather light. There are a number of variants here, all with their various pluses and minuses. Among the more popular, we've got Mak-Newt's, Schmidt-Newts, Mak-Casses, Schmidt Casses and Meade's new(er) ACF.


Meade offers a line of Schmidt-Newt's
that provide the observer with a very wide,
well corrected field.

The most popular is probably the Schmidt Cass or SCT. Available in apertures from 5” to 16”, I won't presume to step on Uncle Rod's toes (he's written the book on them – seriously), but I'd encourage you to drop him a line and ask if you've got specific questions on the design.   All in all, the SCT is an amazingly versatile design. It's fairly small, yet packs a lot of aperture for the size. The eyepiece is nearly always in a fairly convenient location, and they pack a pretty good bang for the buck – especially if you purchase off the used market. If you're a gadget lover, you'll probably want to take a long hard look at the SCT - there's tons of accessories for these scopes.

On the downside, the common mass produced SCT can be something of an exercise in averages, and they can be a bit fiddly as per collimation – and you DO need to collimate these guys. But if you take some time to learn about the design, and how to optimize it, you can get some amazing views.

While I'd say (in general) refractors lean towards the imaging crowd and reflectors towards the visual – SCT's really go both ways. They tend to a jack of all trades. Unfortunately, there's a second half to that quote, but everything's a trade off....


Up Next, Part 2 – Choosing your first bits of gear




Hubble Images Courtesy STSCI: copyright notice
http://hubblesite.org/copyright/



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