Guide To Astronomical Observing Equipment
This guide is intended to give the reader a quick introduction into what equipment can be used to observe many of the different objects in the night sky. It is not an in depth technical discussion or a product showcase but a gentle introduction containing the basic information required to assist you when you venture out to purchase a telescope.
Buying a telescope or binoculars
One of the most often asked questions by the newcomer to amateur astronomy is what type of telescope should I buy? The best answer is often difficult to give, as there can be many factors to be taken in to consideration. Some of these factors are personal, technical and financial, and often the correct answer can only be gained by your own observing experience.
Amateur telescopes come in all shapes and sizes from the 60mm starter telescope on a small tripod to the monster 800mm and larger Dobsonian telescopes seen advertised in the Astronomy magazines or on the Internet. Astronomical telescopes are primarily specified by the diameter of their lenses and mirrors. The bigger the diameter the more light it will collect and the fainter the objects you will be able to see. There are other benefits of having large lenses or mirrors, basically the bigger the objective more detail you will be able to see. There are of course a few down sides to the bigger is better approach, firstly cost, secondly size of the instrument and thirdly our atmosphere is not kind to large aperture telescopes. Sometimes a small telescope can see through the turbulent atmosphere better.
Some high street shops sell telescopes, but the best way forward is to buy a copy of one of the astronomy magazines available, possibly one of the UK based ones, look through all the adverts and then make a few phone calls to the specialist telescope dealers. Armed with the information in this article you could help yourself make a better choice. To do astronomical observations that are fun and rewarding you do not need to be an expert in optics, you just have to know what you can see with any given size and type of telescope and adjust your observational aspirations accordingly. To illustrate the way forward let us choose a few objects to observe. We will cover the technicalities as we go.
The Moon
The moon has held humankind's fascination for thousands of years and it also makes a good object to observe with a telescope or binoculars. The moon is a bright object and it is close enough to allow the unaided eye to resolve some surface detail. So what instruments would be useful for lunar observing. Virtually all types of telescope can be used for lunar observing, cheat I hear you say, no advice here! Well if we consider the smallest usable telescope to be the ubiquitous 60mm refractor which uses a 60mm diameter objective lens to bring the star light into focus. So what can be seen? Your choice of a small refractor has opened up a vast amount of lunar detail, most of the larger named craters and mountain ranges are easily in your grasp at low magnifications, around 30 to 40 times. Your telescope has collected plenty of light for you to use, so you will be able to push the magnification up to the limit for this type of instrument usually around 100 to 120 times magnification and still have a reasonably bright image. You will be presented with a lunar view now so covered in craters and mountain ranges you will need a good lunar atlas to navigate across the surface. By choosing the different phases of the moon to coincide with your lunar observing programme you will be able to see the changes of illumination effecting what you can see. For example many of the larger crater walls cast shadows onto the crater floors below. You will be able to see the different shadow lengths as the moons phases change. The quality of the images seen are usually dependent upon the quality not the type of the instrument you purchase. Many of the smaller and often cheaper instruments provide quite good images at low magnifications but often struggle at higher magnifications as the images get fuzzy and faint. Be very careful of the advertising hype "400 times power", as this is not easily attainable in small instruments. The usual rule of thumb to use is for every 25mm of aperture you can usually use up to 50 to 60 times magnification. To work out the magnification obtained by your eyepiece divide the focal length of the objective lens or mirror by the focal length of the eyepiece. The smaller telescope attached onto the main tube is a sighting telescope through which you will be able to see a larger area of sky compared to the main telescope. This will help you aim the main telescope.
You must make sure that your telescope is provided with a good mount and rigid tripod. Your telescope will be rendered useless if the mount is wobbly or difficult to use. Some mounts are better than others for some types of astronomical use but whatever type is supplied it must be sturdy and easy to use. It is most frustrating and often impossible trying to glide over the lunar surface to check out that crater you saw last night when your telescope is wobbling all over due to a poor mount and tripod.
Another area to check is how many eye pieces do you get? Most astronomical telescopes are capable of using interchangeable eyepieces. You should have one low power, around 30 to 40 times magnification and one high power around 100 times magnification to start with. The low power will be used for general observing and the higher power for more detailed work. If you purchase your telescope from as astronomical equipment specialist they should be able to advise you on what extra bit and pieces are available for a further modest outlay. Another advantage of this choice of instrument is that it is portable and easy to store. You can store it ready to go and be observing within minutes of the clouds clearing, something you cannot do with a larger instrument. If after many happy hours of observing you may want a better or bigger instrument. You will have a large choice of small very high quality 60 to 100mm refractors and mounts costing well into many thousands of pounds. Or you could consider a larger reflecting telescope that will allow you to observe many more objects in the night sky for a modest financial outlay. You can still keep your starter scope because if you chose an instrument that used the standard 1.25 inch diameter eyepieces you should be able to use them in your next telescope.
The Planets and Faint Fuzzy Objects
Having fully explored the lunar surface and observed the planet Jupiter with its subtle colours, spent hours watching the continual dancing of its 4 Galilean moons, you may well feel that you need a larger telescope to see more. You will now have the first signs of aperture fever where you have just got to have a bigger telescope! You want to see a little more detail in the cloud tops in Jupiter's atmosphere and clearer detail in the rings around Saturn. And what about some of those faint fuzzy glows of light your star charts keep enticing you to look at. Do you buy a bigger refractor or buy one of those reflecting telescopes? This is the point where the heart and wallet clash. If you want to see the very best possible planetary images the long standing suggested way forward is to buy a quality refracting telescope. These are expensive and you should be sitting down when the sales person gives you a quote, not to mention the long waiting lists for some manufacturers equipment. You will be looking at instruments with apertures of 100 to 150 mm. Your time with your starter scope will have told you that the telescope mount and tripod must also be of the highest quality to fully utilise your expensive telescope tube assembly, and yes you have guessed it, more expense. But if you chose well at this level you will have an instrument to use for life and of course, that will be good value for money. The alternative approach is to buy a reflecting telescope. The most popular type is the Newtonian reflecting telescope. This type of telescope uses two mirrors to bring the distant light to focus at the eyepiece. The mount and tripod still needs to be of a high quality with the option for some sort of drive and guiding system to track the stars and planets across the sky. For a modest outlay you could now be looking at an instrument with a main mirror of between 100 to 200mm. This larger instrument will collect much more light than the 60mm refractor and you will be able to see hundreds more objects in the night sky. But what will I be able to see? The larger weather systems in Jupiter's cloud tops are now easy to see. The subtle bands on Saturn can now be decerned and the ring system will be a wonderful sight. Mars will start to show some faint large scale surface details, its polar caps will be visible as white polar caps during the Martian winter. The nebulae and galaxies that you have only just glimpsed in your 60mm refractor, (which you have been striving to find by working through the observing lists printed in the monthly astronomy magazines or that observing book for small telescopes you purchased) will now be brighter and show more detail. Having a larger instrument will often allow you to use more magnification possibly up to 200 to 300 times if the sky conditions will allow! Due to the combination of extra light gathering power and magnification many faint objects that you could not see before will be in your grasp. If you want to pursue more of these objects you will have to buy a more specialist atlas or one of the specialist CD ROM's. These have lists containing tens of thousands of objects, (some of which you will still not be able to see unless you buy a monster telescope or address the problem a different way, more later). Turning our attention back to the moon you will be overwhelmed at the detail available. What about photographing some of these objects. The company that sold you your telescope will be able to advise you on what you need here, suffice to say that camera adapters are readily available for most makes of camera. Your decision to purchase an instrument in the 100 to 200mm class will also force you to think about storage problems. You may also need a helping hand to carry and set up the telescope safely if you purchase one at the larger end of the scale. If however you still want to see many of these objects with out the attendant expense of a fancy mount and tripod you can purchase a reflecting telescope mounted on a simple movable base. This type of telescope mount is called a Dobsonian. The Dobsonian telescope has really opened up the possibility of owning a large aperture reflecting telescope for a modest outlay; there are also small Dobsonians available. For the more adventurous there are Dobsonian kits and plans available, so if you enjoy a challenge you could build your own telescope. You could even grind your own mirror instead of purchasing a ready made one. This will save you a little money and give you the added thrill of seeing an image formed by the work of your own hands. The information and techniques required are beyond the scope of this article but once again there are books available and a few Internet sites specialise in telescope making. Even if you get stuck on a problem help is never far away.
The Really Faint Stuff
Now that you have been looking at the wonderful images of galaxies in the magazines and on the Internet you may want to track down many of these really faint galaxies and nebulae visually this will require a large telescope. You are now limited to a large reflecting telescope unless you want to sell your house and your car etc as you will need plenty of money for your dream refracting instrument and observatory. Luckily the Dobsonian reflecting telescope comes to the fore here as main mirror apertures of up to 500mm (and above) can be obtained. You will not be able to see colour images like the books show but you will be able to see countless galaxies and nebulae with your own eyes. Your major problem will now be the quality of the site you observe from. If you want to get the best from your dream instrument you will have to observe with it from a dark site. This of course means that your Dobsonian will have to be transportable, which they are, You will need a car with a large boot (or an observing partner with a car with a large boot, They can also help you assemble the telescope on site as well!).
An observing bag containing your sky maps, red torch, warm clothes and a flask ready to go to your chosen site away from the light and industrial pollution, or as far as you can reasonably go in the UK. You can still observe from your back garden, and see many objects, but using your telescope from a dark site is well worth the effort. Those galaxies just visible in your small refractor as fuzzy stars will now start to have definite shapes. In some of the larger ones you will be able to start seeing some detail with the structure of some galaxies starting to become apparent. The planets and the moon are still out there for you to view and they will look wonderful.
There is also a further class of telescope, which use a combination of mirrors and lenses. These come in many optical configurations and sizes. They have mirrors and lenses range from 90mm to over 400mm in diameter. These telescopes pack a large amount of light collecting power into a small space. Virtually all the telescopes in this category come with a fork mount of some design to which is attached a heavy duty tripod.
The name of their inventor is usually used to describe the optical configuration, so you will see these telescopes called Schmidt Cassegrain's or Maksutov's. The smaller versions are ultra portable with good image quality to boot! Some owners pool information on the Internet with pages dedicated to some of the smaller telescopes, help is out there!
Key Pad and Computer controlled Telescopes
Many telescopes of all optical configurations and sizes from the larger manufacturers will have some form of key pad control built in or the capability of adding it on later, your dealer should advise you on the upgrade paths available. With this type of telescope the user uses a small hand held unit to control the pointing of the telescope. By selecting the desired object to be observed from a menu displayed on the controller screen the telescope will move to and locate the selected object positioning it within the field of view of a low power eyepiece ready for you to observe. Indeed most of these instruments can be controlled from a personal computer thus opening up the possibility of a celestial feast of normally difficult to locate objects at your finger tips. This type of control opens up the sky for anyone, even a complete novice. With the latest class of battery powered computerised telescopes you can be observing within a few minutes of the clouds clearing and you stepping out side.
A second avenue to explore here is the availability of specialist electronic cameras available to the amateur astronomer. Whilst your computer is guiding your telescope around the night sky why not let it take pictures for you? Some excellent images can be taken with this type of set up, but as usual with any venture, to get the best out of any system you will have to work at it. You will be able to image objects you cannot see or photograph with a conventional camera, providing you have pointed the telescope in the correct place! Indeed you will be able to image objects that the professional astronomers struggled to capture only 25 years ago with their telescopes. Using electronic cameras may also be the best way to effectively increase the size of your telescope.
There are so many different types of telescope available today with different attributes; the choice is nearly endless. To give you a flavour of the amount available, a recent astronomy magazine contained advertisements for over 65 different telescopes, makes, sizes, types etc. To briefly sum up this huge array, you will be able to purchase a simple refractor with a 60mm objective lens on a small tripod or virtually any size of refracting instrument, some at very competitive prices up to a 150mm state of the art masterpieces. Newtonian reflecting telescopes start at around 100mm and extend up to over 800mm Dobsonian monsters. The Schmidt Cassegrain and Maksutovs configurations start at around 90mm and extend up to 400mm. There are also suppliers who will build you one off specials if you cannot find what you require from the big commercial suppliers. Many of the telescopes available today will not disappoint if chosen correctly. The differences between competing brands are often small and the performance difference between alternative designs can be small when comparing broadly similar apertures. You should choose your telescope with what you want to observe in mind. It is no use buying a high quality 100mm refractor when you need the light gathering power of a 300 mm reflector to see your faint objects. Likewise if you become interested in the moon and planets the 100mm refractor would be a good buy.
Binoculars
A good introduction to telescopic observing comes from using binoculars. Once again please purchase them from a good astronomical or photographic dealer. A good starting point is the standard 10 * 50 binocular. These instruments have two lenses of 50mm diameter and will provide a 10 times magnification. They are small enough to hand hold and relatively easy to keep still, except when you are cold and tired! This size of instrument can provide some stunning views of the Milky Way and star clusters. The moon will not be a disappointment either. If you are out observing with your telescope your binoculars can be very handy for having a quick look to help you home your telescope in. A pair of 10 * 50 binoculars will project a beam of light 5mm in diameter out of the eyepieces, the diameter of this beam is a good match for most observers dilated eyes when they are observing. Looking for those comets reported in the astronomy press is often easier with binoculars.
There are a few books to aid the binocular observer of the night sky; they are well worth having a look at. If the binocular bug bites you, once again you can buy larger instruments. A popular large size is the 20 * 80 (20 times magnification and 80 mm diameter objective lenses) instrument. These provide really excellent views but they are on the limit for hand holding, as your arms soon tire! They work very well on a sturdy tripod, as would any pair of binoculars. If you need any bigger binoculars, 25 * 100 could be to your calling, of course a tripod is a must at this size, if you need to go further up the scale 40 * 150 are about the largest commercially available. These instruments are tripod mounted and very good. A few comets have been discovered with this size of instrument. These binoculars are also very expensive!
When choosing binoculars ask if you can have a look through them. You will have to adjust the inter pupil distance of the binocular eyepieces to suite your eyes by pushing or pulling the two sections together or apart, this may take a few minutes but it is well worth it. Try and focus on an object around 100 meters away with the sky in the background, please be careful and do not look at the sun when testing binoculars or any telescope. Television aerials and electricity pylons make a good target. If you can see coloured fringes around your chosen object, try another pair or a different manufacturers model until you find a pair that gives you a good clean sharp image throughout the field of view. The chosen pair should now serve you well with good astronomical views.
Although this article has been focussed on telescopes and binoculars there are many different supporting pieces to help you enjoy the night sky. A good night sky atlas is a must to navigate around the sky, there are a few to choose from so your choice will be a personal one. The thrill of tracking down an elusive faint galaxy or double star is not to be underestimated. Likewise the computer now plays an ever growing part in our leisure time (like it or not). Luckily astronomy and telescopes work well with the computer, as there are many pieces of software available from virtual planetary tours, advanced sky atlases and even voice control software for some telescopes. The telescope builder is also well served both by the computer and the Internet.
We have just done a quick tour of the size of telescope required for seeing different objects in the night sky. But we have not discussed many of the differing types available. As you will find out by looking at all the adverts in the astronomy magazines there are many types to choose from. The basic requirement of a telescope is to produce a high quality image in an instrument that is easy to use. A high quality image is delivered by having good quality optics that are well collimated (correctly adjusted) and a sturdy mount. A telescope that is easy to use should also be quick to set up; those clouds come over faster than you think! Any telescope has to be reliable, you want to be looking for the faint galaxies not your tool kit!
