Tools of the Trade
The amount of equipment available to the amateur astronomer is staggering. This is just an overview of the most essential items an amateur astronomer would need.
Amateur astronomers have two basic types of mounts to choose from: the Dobsonian mount and the more familiar equatorial mount. Each has its pros and cons.
The Dobsonian (or Dob) is the easiest to learn how to use: it simply moves up/down, left/right. Any star party you go to will show how popular they are: most beginners start with this style mount. Only reflector-type telescopes are mounted on Dobsonian mounts.
One drawback of the Dobsonian mount is that the base can be heavy. Plus, as I’ve found out the hard way, the part on the bottom that is supposed to remain smooth and flat so it can rotate smoothly can get dirt in it and make the rotation of the base less smooth.
The equatorial mount is what most people unfamiliar with amateur astronomy think of when they think of telescopes.
The equatorial mount’s good point is essentially another of the Dobsonian’s drawbacks. The German equatorial mount, when aligned with the stars properly, can continuously follow an object across the sky by turning only one knob. Alternatively, an equatorial mount can have a motor attached to it and the motion of the stars can be followed automatically. This makes this mount the only choice between the two for astrophotography (taking pictures of objects in the sky). This isn’t possible with a Dobsonian mount, as to follow an object you must move the scope on two axis manually.
Conversely, the equatorial mount’s alignment feature can be considered a drawback because it takes some time to align the three axis to properly follow the stars. Plus, the user has to wait for at least three stars to be visible to be able to align it. Not so with a Dobsonian’s mount: Just plop your ‘scope down on the ground, point at your object, focus and there it is. Not to mention the fact that if it’s partly cloudy, there may not be three suitable stars to align to at all!
Contrary to very popular belief, a telescope’s job is not to make those incredibly small dots of light bigger, but to collect as much light as possible. Enlarging the image (magnifying it) is secondary. How a telescope collects that light can be done in several ways. The diameter of the objective or primary (its mirror or lens, depending on the design) is the main identifier of the type of telescope. This is called the telescope’s “aperture”. See “Lesson Time!” for a more thorough explanation of the various measurements associated with a telescope.
The diagram to the left illustrates why it is called a reflector. Isaac Newton designed this type of telescope, so it is commonly called a Newtonian.
The upside of the reflector is that, for the size of the objective, they are relatively much cheaper. The simple design is the reason for this. A Newtonian is simply a tube with a concave mirror at one one, and a smaller, secondary mirror near the other end, which is where the eyepiece goes, as you can see in the diagram.
This is probably the most popular of the three major designs – mainly because of its ease of use and the fact that when mounted on a Dobsonian mount (described above), the combination of a reflector with a Dob mount will drop the price significantly (as compared to a traditional equatorial mount). An 8″ reflector costs around $350 compared to a 4″ refractor for about $400.
The traditional and familiar refractor design. This design is considered ideal for planetary viewing in particular. Unfortunately, as the aperture (objective lens) increases beyond a certain size, optical aberrations (slight distortions and odd coloring) increase. But this has been alleviated considerably with an apochromatic design. (A big word, I know. And please don’t ask me what it means!)
There are several designs similar to the Schmidt-Cassegrain (or SCT, or Schmidt-Cass), including the Ritchey-Chrétian, and the Maksatov-Cassegrain (Mak-Cass). They vary mostly in what happens to the light path inside the scope body. Meade has popularized the SCT with its fully computerized little scopes.
SCTs are known for their superior optics, and most SCTs are motorized. This combination makes them ideal for astrophotography. Plus due to their compact size they are easier to move around for the aperture. These features run up the price considerably, though – a 5″ Meade starts at around $1,000. Meade SCT
Another nice feature of SCTs is that they are usually fully computerized, meaning once properly aligned, the motors in the mount can follow an object throughout its path in the sky. As for getting it properly aligned, some now have GPS installed so that all you have to do is put it down on a level surface and it will automatically align itself! (But you’ll pay a pretty penny for these neat features!)
Typically, SCTs and the like are mounted similar to the one pictured on the right. However, SCT-style ‘scopes can be mounted on equatorial bases.
Though many people don’t realize it, binoculars are an excellent (and cheap) way to get started in amateur astronomy. Most amateur astronomers have them to quickly find an area of stars. Many things in the sky are best viewed with binoculars. Sizes recommended for astronomy range from 8 X 40 and up. 10 X 50s are typically considered the optimal size and magnification. Any higher magnification and the image will get too jerky to view effectively.
However, for people who want to get binoculars with larger magnifications, there are designs on the Web for building a binocular mount that holds them securely in place while viewing – or mounts can be bought.
Eyepieces are separate from the telescope and are switched out frequently, depending on what you are looking at and how high or low of a magnification you may want. There are a great many choices when it comes to eyepieces. They are distinguished by their focal length, which ranges from as small as 4mm to around 40mm and up.
Remember, the smaller the eyepiece focal length, the greater the magnification. Backwards, I know, but I didn’t make up the rules of light physics! See my explanation about the relationship between focal length and magnification in “Lesson Time!” below.
Types of eyepieces include varying focal length, eyepieces with a reticle (cross-hairs) marked in seconds and arc-seconds for precision measurements, and wide-body eyepieces for a wider field of view. Eyepieces can get pretty pricey. A basic, small (but decent quality) eyepiece starts at around $50. High quality eyepieces with some bells and whistles can get upwards of $400!
Eyepieces also come in two barrel diameter sizes: 1.25″ and 2″. 1.25″ is more common, mainly due to the price difference, but most ‘scopes made now are made to fit 2″ eyepieces with an adapter for 1.25″ eyepieces. The benefit of 2″ eyepieces is that you can see more sky at a time than a 1.25″ at the same magnification.
Many telescopes sold in department stores are only made to fit a third size of eyepiece: .965″. If you are ever looking at a ‘scope at a store and it has that eyepiece size, run away! It is most surely a cheaply made telescope and not worth the box it comes in.
The focal length is very important in astronomy. The first term you need to learn is the “objective” or “primary”, which is either the large mirror on a reflector, or the first lens the light goes through on an eyepiece, refractor, or SCT. Focal length is defined as the distance from the objective to the point where the light path comes together – the diagram for the refractor shows this. In that diagram the light path is the dashed line inside the scope.
Now, to confuse you even more: magnification is defined as the focal length of the telescope divided by the focal length of the eyepiece. So when I put a 15mm eyepiece in my reflector, which has a focal length of 1500mm, I divide 1500mm by 15mm and get a magnification of 100x. But if I want to be able to see more detail (in practical terms you could say you want to get a “closer” look at the object), I could use a 10mm eyepiece. That would give me a magnification of 150x (1500mm / 10mm).
Maybe that explanation will help you realize why advertising the magnification of a ‘scope means nothing in practical terms. What is important is the focal lengths. Plus, every telescope has a limit to its effective magnification. If you see a telescope that is being advertised by its magnification, run the other way! It’s a sure sign that it’s a cheap telescope.
Filters have very specific uses. There are a large number of filters used for planetary viewing. These come in many colors and each highlights different features of the planet you’re looking at. There are also specialized filters, called narrow-band and broadband filters, that are used specifically for viewing nebulae, plus they have the added benefit of blocking out some light pollution.
Nebulae emit certain gasses (mainly hydrogen and oxygen) and some nebulae emit more of one particular gas. Each of these gasses are seen at a particular wavelength on the visual spectrum. The filters filter out most of the spectrum except the wavelengths that a gas can be seen at, greatly increasing the visibility of the nebula.
I started out my hobby with a lucky shot on an excellent book: “The Backyard Astronomer’s Guide” by Terence Dickinson and Alan Dyer – both giants of amateur astronomy. This book has information on everything someone who is just starting out could need. The book covers in detail all of the current equipment, things to look at, how to make the right decision on what to buy, and what not to buy. In short, it was the perfect book to get me started.
Then there are books with a specific “target”, so to speak – it covers certain types of objects to look at, but goes in to detail about them. The next book I bought was “Star Watch” by Philip S. Harrington. I bought that book because it gives very clear directions on how to find over 125 objects. Great for the beginner. Another must-have first book is “Turn Left at Orion” by Guy Consolmagno and Dan M. Davis. It is a very popular book and every object in the book was found within 15 miles of New York City with a 4 inch refractor!
Finally, there are star atlases. They are exactly what they are called. The sky is laid out in “latitude” and “longitude” (called declination and right ascension, respectively, when talking about the celestial sphere), in a similar fashion that an atlas of the Earth is laid out. The price for a good atlas starts at around $50, so typically it’s best to get a hold of a couple and decide what is best for you and your needs. I’ve visited many forums debating what is the best star atlas and I’ve never seen any two people come to a consensus.
Accessories and Miscellaneous Equipment
There are so many other things that can be useful (and not) for the amateur astronomer. A red light is a must. Dark-adaption is essential and no amateur astronomer hates anything more than white light when they are out observing.
After staying out for a couple of hours, inevitably dew forms on everything – especially glass and metal, the two things telescopes are made of, mostly. Dew on the objective and/or eyepieces can immediately stop a viewing session. That’s where “dew heaters” and “dew shields” come in. Dew shields are found more frequently on SCT and refractor designs – mainly because the primary mirror or lens is near the opening of the tube, and therefore more directly exposed to the air. Newtonian reflectors have their own dew shields built-in, as the primary mirror is way down that long tube. Dew heaters, on the other hand are put on the eyepiece, the finder scope (the small magnifying viewfinder mounted near the eyepiece), and pretty much anywhere the light path needs to go through or bounce off of a lens or mirror.
With all of those heaters you need some way to power them. There are power supplies for amateur astronomy. And some amateur astronomers use car batteries to power their heating systems.
There are also special chairs for observing. The Denver Observing Chair (so named because it was designed by members of the Denver Astronomical Society) is very popular because the materials can be purchased for $30 or less and can be made with common home tools.