Jump to content


- - - - -

Hitchhiker's Guide To Astronomy

These days you can't just grind your own mirror in the basement, buy some Kellners and enjoy the night-sky from your back yard. Astronomy has been improved immensely by the internet and companies that truly understand marketing. If you want to succeed in this exciting new incarnation of the hobby, you need to be prepared to pay the price of admission and avoid potential mis-steps. This guide is intended as a short introduction to the major aspects of astronomy as a social phenomenon. It will acquaint you with the basic concepts and principles you will need to run with the pack in the 21st century!

Types of Astronomers

You want to be with the in-crowd when engaging in a hobby so dangerously close to geeky scientific pursuits, so learn to spot the right people in any group.

Experts/Experienced Amateurs (the group you want to be in):

Most importantly, "experts" have spent several tens of thousands of dollars on optical tube assemblies (OTA's) and eyepieces, generally preferring an instrument and eyepieces that meets the following criteria:

  1. objective diameter does not exceed eyepiece diameter by more than 2:1 ratio (it is considered bad taste);
  2. Any instrument from a big three maker (infra) must be accompanied by an excuse, such as "Though my 42mm APO from X is a real gem, I wanted a more grab and go scope for the backyard, so I bought this 16" reflector" Experts in training are often allowed to buy big-three instruments by professing that they are saving money for an apochromatic refractor (q.v.) of notably restricted aperture.
  3. The star test must be perfect; even though its results are dubiously applicable to in-focus images, the knowledge that you have a scope that star-tests well will give you the self-esteem and confidence you need to appreciate the delicacy and subtlety of objects you are viewing. An expert will perform a star test at least every twenty minutes.

Generally experts also meet the following requirments:

  1. Observing is a serious business: not only must you appreciate the delicacy of texture and subtlety of coloration of whatever you are looking at, you need to look at lots of things. Finding and fully appreciating a lot of objects that look like small grey specks to novices is what astronomy is all about -- you don't want to linger and just look at stuff like some novice.
  2. You have discussed your eyepiece's design on the phone with Al Nagler or gotten tech support for your telescope from Roland Christan.
  3. You are retired, wealthy and/or your wife likes you to spend lots of time away from home, especially at night
  4. It would never occur to you as ridiculous that you just spent the GNP of some African countries on a 4" refractor to get the extra "oomph" over your old 90mm
  5. You must have a specialty, excluding lunar and in most cases planetary observations, since any yahoo can see those things.

The best specialties are galaxies under 1 arcsecond and/or dimmer than 18th magnitude. Also good are open clusters in other galaxies or globular clusters anywhere. By spending enough money and using averted vision (q.v.), you should be able to achieve a sort of space-trance in which you convince yourself that the grainy dust-mote-sized ball you are looking at is stunning! Do be extremely careful, however, picking a speciality: once you have declared your interest and become an expert, it is bad form to look at other types of objects. Example, you decide that visual examination of objects from the 2MASS survey is what you need to spend your money and time on. After you have established this as your area, you must avoid looking at planets and curse any and all lunar appearances, even if you might really enjoy taking a quick look at Posidonius. If you get caught, you may clear yourself by claiming to be testing your optics with the authoritative "craterlets in Plato" test, but make sure you see at least 10!

Also, some specialities that seem good are really not. For example, double-star work, since it requires good optics and favors unobstructed tubes would seem ideal at first, but there are several reasons not to take it up: a) high magnifications required generally obviates need for expensive wide-field eyepieces; B) there are some well-known limits to resolution; c) the math implied in common terms such as "angular separation" makes this a nerd's racket. Similarly, while you may most enjoy the "multi-colored splendor of unidentified open clusters", don't make the mistake of trying to analyze stellar spectra or anything of that sort!

Industry Experts:

These are the celebrities of your hobby. They are generally altruists, good listeners and scrupulously honest; most completely transcend self-interest. You know this because you have met them, if you are an expert.


Novices are in all ways the most pathetic type of astronomers. They have been known to spend less than a hundred dollars on all their equipment combined and then compound this transgression by spending a long time looking only at truly spectacular sights. Some have been known to look at the moon with 60mm refractors and think it was interesting, obviously ignorant of the delicacy and subltety of detail they could see in the Virgo cluster instead. Or, perhaps worse, they pretend that their 10" Dobsonian's diffraction spikes are not a big deal and that they can actually see more with it than the expert with an exquisite 30mm apochromatic refractor. Try not to hang out with novices unless you intend to take them under your wing and recommend significant upgrades to their equipment.


Spend even more than experts, with distinction that they favor large apertures and usually no eyepiece and occasionally know what they are talking about. Do not associate with them.


These are the less and less common, since they tend to avoid crowds. Fortunately, younger nerds are probably not inclined (or cannot afford) to pursue astronomy and are more likely to be drawn to computers. Typically nerds will be too busy conducting measurements of some esoteric nature to be a threat to your social status.

Observing Techniques/Other Terms

"Averted Vision": Expert turns head, squints eyes and pretends to see barred-spiral structure in very dim, distant galaxy. One occasional faux pas with this technique is that it is performed in front of ignorant novices or professional astronomers while the scope cap is still in place; also make sure the drive is turned on!

Dark Adaptation: If you have children, just say: "No, honey, those men are not pirates." Otherwise, practice and exhibit your dark adaptation at every opportunity, e.g., "Do those EMT idiots realize they are destroying my night vision with their headlights!"

Seeing: While some have tried to rigorously quantify seeing, it is by nature a fairly slippery concept, which can be useful -- it will be unique to your specific time and place. When talking to your fellow astronomers, for example, it is better to say that the seeing in your location was awful despite promising transparency rather than admitting that you just felt more like staying in and watching re-runs of "News Radio". Or, you might find that a night of spectacular seeing allowed you to detect Charon as a tiny disk (and perhaps some hint of detail with averted vision).

Dawes Limit: Strictly the minimum angular separation of equally bright stars detectable by a telescope of a given aperture. The proper application of this formula is to make sure that your new telescope can split a pair of stars at a separation slightly larger than would be indicated by its aperture; otherwise, there's not much further use for this kind of formula.

Magnification: While magnification is at its simplest the focal length of the objective divided by the focal length of the eyepiece, it is at times a source of almost religeous contention. As an expert, you are well-advised to favour zealously either a low-magnification or high-magnification approach. For example, if you are an expert on the outer planets, you might say that you prefer to use a low magnification in order to frame Neptune and its moons with a gorgeous field of stars. Conversely, you might favour a higher magnification approach to work on globular clusters, so that you can increase the contrast of the surrounding sky and zoom in on one or two of the more interesting stars. As a rule of thumb, the best magnification is usually the one rendered by the focal length of the eyepiece you paid the most for.

AFOV (Apparent Field of View): AFOV in eyepieces is a non-linear function increasing with price and mass, with a sharp change in slope at around 50 degrees AFOV. You can always count on at least 50 degrees AFOV being usable, with some distortion around the edges.


In a hobby like astronomy, which was only recently rescued from geeks, you have to have the right gear. Telescopes (OTA) and eyepieces are critical. Luckily, there are not a lot of acceptable options, although the market seems full of products. Knowledge of 6 brands is adequate for good standing in the fraternity. What you want to say with your equipment is this: "I know enough about astronomy to recognize the best, and I care enough to spend whatever it takes for that little extra something that others acknowledge after spending their money to buy the same thing."

Astrophysics (AP): Top of the line APO refractor OTA's. Not only do they cost as much as a good car, the waiting list is now approaching infinity. This combination makes their quality inassailable. The cynical and jaundiced might point out that there would be very few people honest enough to criticize an instrument they just spent 20K and 10 years waiting for, but those people are not experts (q.v., q.e.d.).

Takahashi (TAK): Only slightly less desirable than AP. Though they cost more, they are generally produced in huge quantities of several dozen per year, making their quality a bit suspect.

Televue (TV): Truly affordable in comparison to AP and TAK, these instruments are only about as expensive as a reliable used car. While the quality is obviously better than the "big three", it cannot compare with AP and TAK, due to lower price and higher availibility. The stars of the TV line, remarkably, are two achromatic refractors, the Pronto and Ranger, which even experts are allowed to have as travel scopes, although they exhibit chromatic aberrations that would scare children in a 60mm Tasco refractor. Not to worry, however, TV makes most of their money on the high-end eyepieces, some of which are bigger than the Ranger and Pronto.

Meade, Celestron, Orion, aka "the big three": These companies obviously care nothing for astronomers or astronomy; if they did, they would make fewer instruments and charge more money. The only consistent exceptions are:

  1. short tube 80 variants as a backpacking scope -- should never be used at home
  2. 10" or larger reflector/SC as quick look or imaging scope
  3. eyepieces on sale when you are paying off/saving up for your AP, TAK, TV equipment

Others: Risky. While a small or otherwise obscure company may produce a good quality or adequately priced instrument or eyepiece, you want get the name recognition and brand identity that is so essential to your development as an astronomer. Judging equipment by what you can see with it opens you up to criticism from others without the warm protection of fellow users. Alternately, sometimes an expert can use uncertainty to his advantage, e.g.:

"This AstroRaqet ($4950 for OTA from Bluto and Oyle Optical) utilizes a 43mm objective made from the bottom of a 61/2 oz. coke bottle amd SDF glass with a Yolo-inspired optical path, resulting in optical quality and resolution that is only _just_ short of exquisite for my work with asteroid occultations of galaxies in the Virgo group. Several of my fellow observers have been stunned by the quality of images offered on the planets, and the compact multi-tubed design never fails to get attention at star parties."


Televue: TV eyepieces are the only ones consistently expensive and large enough to justify their use. Al Nagler wisely takes the best ones out of production quickly so that they retain their value, so don't worry about the cost, as it is an investment.
Everyone else: Don't even consider it -- you may get lucky and see something in the eyepiece that looks similar to what an expert sees in a Televue, but you won't get the "space-walk" feeling or that undefinable something you need to feel good about your hobby. Some possible exceptions are certain orthoscopics, with the stipulation that they are no longer in production. Also, you can sometimes use big-three eyepieces if the better eyepieces adversely affect your custom Dobsonian's balance or you fear your neighbors/kids/family might not appreciate the view of the better eyepieces or might possibly put a bit of eyelash against it.

Telescope Designs


Achromatic: Design using two-element crown and flint glass objective. Can only focus a sub-set of the visible spectrum, thus will display a violet nimbus around very bright objects. There are at least four objects in the universe bright enough from earth to make this a problem, so it is advisable to spend at least 5K more for an apochromatic refractor. Only acceptable design in certain small scopes from Televue.

Apochromatic: Design using (typically) three-element objective, with the third consisting of a special type of glass. The better brands use glass that is not only rare and expensive but also (preferably) prone to break with normal changes in temperature. Apochromats are thus able to focus three colours, but their capabilities do not stop there. In many cases, the owner of an apochromat of 50mm or less is able to detect subltety of texture and delicacy of coloration in objects that took years for the 200 inch reflector at Palomar to find. This type of telescope is almost always owned by experts. Experts generally use these instrument to demonstrate the fact that they can achieve dangerously high magnifications on large, bright objects as well as to view very small or faint objects at extremely low magnifications.

"60mm"/"Department Store Telescope (DST)": These are a special class of achromatic refractor (typically) which should never be used for astronomy, since fewer than 99.9% of the more interesting astronomical objects can be seen with it. One real sign of an expert is that he will spend a lot of time talking about how his 40K investment leaves the 40 dollar department store scopes in the dust. Ironically, Huygens and Galileo (not to mention Messier possibly) are thought to have made some serious discoveries with this class of telescope. Of course, Huygens and Galileo did not have the shaky mounts and inferior coatings of DST's to worry about...not to mention the light pollution or the limited eyepiece selection amateurs have to deal with nowadays.


Newtonians(including Dobsonian mounted(q.v.)):

These designs use a parabolic mirror as an objective to focus light and therefore do not have any problem with secondary color. Unfortunately, these designs are plagued with a very high aperture for the dollar and are widely available. Also, diffraction spikes from diagonal supports can be seen on a a handful of brighter objects, making these instruments useless for the serious astronomer. Some mirrors, however, are exceptional and acknowledged to be good even by experts. Those mirrors almost invariably are no longer made.

Off-Axis Reflector: Mildly interesting currently due to lack of diffraction spikes and fairly high cost.


Schmidt-Cassegrain: Once considered very good, even by experts. Now commonly available, so not recommended. Similar to Dobsonians/Newtonians inasmuch as they may (in larger apertures) appear to have better resolution and light-gathering capabilities than apochromats, but every expert knows that this is not the whole story -- the obstruction of the secondary (which reflects light to the eyepiece from the concave primary) reduces the contrast to the point where they are almost equal to "department store telescopes (q.v)".

Maksutov-Cassegrain: Still considered interesting in larger apertures (>6") due to higher cost and smaller secondary obstruction (when compared to SC). Older models from the time when a 3" Maksutov cost the same as affordable housing were once considered capable of performance equal to the best apochromatic refractors.

Other: While other designs exist, they are not generally capable of the exquisite performance and name recognition you need to succeed in astronomy.


This is one of the few areas still available for individuality. Whereas the old wisdom was that the mount is more important than the telescope, the new ethos seems to be anything goes, although a few rules apply.

  1. If you are using an equatorial mount, do not use the setting circles. GOTO is OK if the mount costs more than your car, otherwise, it is just a cheap crutch for newbies.
  2. If using a dobsonian mount, try to do everything possible to make it clear that the mount is non-stock. The best options are using piano-grade hardwoods and finishes with brass fittings which require constant care and attention or to try to rig up some kind of tracking platform that will make your Dobsonian track as well as the cheapest EQ mount. In some circles, you can become a semi-heroic figure by knowing brands of cabinet materials and the right emollients for them. Insist on Ebony star bearing surfaces and keep them slick with something that can only be obtained with a hazardous materials permit.
  3. The alt-az mount is the most dangerous choice, since many experts have strongly held opinions on brands and types. You should never use an alt-azimuth mount designed for astronomy unless it was sold by Televue. Most experts find that alt-az mounts designed for other applications feel much better, especially if you exceed the original payload of the mount by 200% with telescope and eyepieces.


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics