Beginners Guide to Astronomy

'I am interested in Astronomy and want to buy a telescope. What should I get?'

This question or variations of it has been asked many times. The question has been posed by people from all ages and walks of life, by school children, parents (wanting a telescope for their children), adults and the retired. It is not a straightforward question to answer. In general, the answer to the question is a few questions to ascertain what exactly the would-be telescope owners experience of the night sky is.

Answering a question like 'What constellations can you find?' is a good starter. If you can only reply something like 'none' or 'I think I know the Plough and Orion' then suggesting buying any type of telescope is bad advice. A telescope magnifies a very small area of the night sky and so it implies that a knowledge of where to point it is required. Also important is an understanding of the heavenly object that is under scrutiny and an idea of the telescope's capabilities. It is true that the moon and some of the planets are fairly easy objects to aim a telescope at, but most other interesting objects, including details on the planets are dim, subtle and diffuse even in telescopes of moderate size. To simply buy a telescope of any type, unpack it, set it up and point it at a bright star or randomly point it, without an understanding of the telescope's capabilities or the night sky has a good chance of leading to disappointment, frustration and disillusion. This is especially true if the expectation is of views similar to what are seen on the NASA web pages.

Our advice to those with limited knowledge of the positions of objects in the night sky is to get a planisphere or star map from a book shop and using only your eyes get acquainted with the constellations and try to find the brighter deep sky objects like the Pleiades, Andromeda Spiral galaxy, Orion Nebula and the Perseus Double cluster. Even though the Andromeda spiral galaxy is a faint diffuse smudge on clear dark nights with eyes alone, the enjoyment is the knowledge of viewing a system of over a thousand million stars whose light has taken over two million years to reach our planet Earth. Likewise when the Orion nebula is seen as a tiny faint glow in the winter months the knowledge that it is a vast region of gas and dust that spans many light years across illuminated by relatively young stars within it, and probably formed from it, is quite a wonder. If learning the major constellations is done over a period of weeks or months then an appreciation of the apparent movements of the night sky is achieved.

There are various books available like Collins Guide to the Night Sky that describe the constellations in more detail. Star names and other objects are listed together with more detailed maps of how to find them and the nature of the objects themselves i.e. nebulae, star clusters, galaxies and double stars etc. When a book such as this is obtained a whole new understanding of the night sky is within reach especially if used in conjunction with a reasonable pair of binoculars. The constellation profiles within the book high light objects that are not visible with naked eyes alone but can be glimpsed using binoculars. Binoculars come in a variety of shapes and sizes, but in general a pair with lenses greater than 40 millimetres in diameter and magnification less than 12 that do not produce blurred and/or double images of stars are adequate. Binoculars are fairly common and if lucky they may already be possessed or perhaps a friend or relative may have a pair they are prepared to lend. We have seen binoculars of reasonable quality for sale in second hand shops, on market stalls and car boot sales for under twenty five pounds. There is an element of risk when buying binoculars from second hand dealers because it will usually be daylight hours. Examine them for damage such as badly scratched lenses and dust or mould within them on the lenses and prisms, this a good sign as to the care the binoculars have had. Try them on a distant object, say a bird on a wire against a plain light back ground like the sky (well away from the Sun) before deciding whether to purchase, if there is a hint of a double image then they are best left. Spend time trying to get optimum focus on both halves by using the central focusing knob and the adjustable eyepiece generally on only one side so as to correct for any difference between left and right eyes of the user. If they will not focus then leave them.

Binoculars are an ideal intermediate step to a telescope because they have a large non-inverted field of view compared with an astronomical telescope, it is easier to relate star formations seen in binoculars with those on a star map when searching for objects not visible to the naked eye. Full concentration can be focused on getting to grips with the night sky rather than setting-up and adjusting a telescope. It is interesting to compare binocular views of say the Andromeda Spiral galaxy or the Orion Nebula with those with the naked eye. By estimating the angle between the brighter stars in multiples of the field of view it will be possible to locate objects invisible to the naked eye such as the whirlpool galaxy in Triangulum, the Crab nebula supernova remnant and the Dumbell planetary nebula. These objects all appear dim and diffuse in binoculars but there is a sense of accomplishment in finding them and appreciating what they are. There are plenty of objects that can be seen in binoculars and the joy of using them on dark moonless nights never goes away. There are however objects that are not suited to binoculars, because of their limited light gathering and resolving power capabilities, such as planetary detail and double stars which will require a telescope to view in detail. A good telescope will show nebulae and galaxies in more detail where binoculars will just hint at. Knowing where objects in the night sky are to be found which have been learnt using binoculars will certainly help if a telescope is ever obtained.

So far we have not recommended a telescope, but instead a suitable way to build up to one. If after doing something like that outlined in the previous paragraphs the urge for a telescope is still present then it is important to be aware of the characteristics of the many types and sizes of telescopes available to be purchased or even constructed at home. We are regularly asked to help someone set-up a telescope who has bought it or been given it as a present but has effectively no knowledge of its capabilities or what they can reasonably do with it. These telescopes tend to be relatively small refractors or reflectors that are available by mail order or in the High street photography shops. There are an awful lot of these types of telescopes barely used in their original boxes hidden away in attics and garden sheds all over the country because the owner has not set them up correctly, been unaware of their real performance, not known the type of object suited to them and where to find the objects in the night sky. This combination of events often leads to the end of any interest in astronomical observing which is a pity since there are generally objects that can be seen with High Street type astronomical telescopes. There are telescopes which are sold as 'astronomical' telescopes that are to be avoided, these are the table-top type refractors that are usually found in toy shops. These normally have stopped down single element plastic objectives lenses on very flimsy mounts, the best that can be expected from these is a blurred discoloured image of the moon showing no craters. The High Street photography shop astronomical telescopes are of better quality than that first used by Galileo in 1609. Galileo built himself a refractor and made quite a few discoveries even though his telescope can only be described of poor quality by today's standards. You should be able to see all Galileo's discoveries and more with a telescope from an outlet such as a camera shop. However to do this requires an understanding of the capabilities of such telescopes.

Telescopes sold in camera shops, mail order and perhaps department stores are generally advertised stating their maximum magnification say of perhaps 300 to 400 times, to use a telescope at these magnifications is quite unfeasible, to do so enhances all the imperfections of the optics, size of optics, telescope mounting and the sky seeing conditions. To achieve good images of astronomical objects at these magnifications requires telescopes of larger aperture and quality not generally sold on the High street.

High Street astronomical telescopes come in two main varieties, 50 to 60mm refractors or Newtonian reflectors with apertures around 100mm. Either can be altazimuth or equatorially mounted. We would not recommend purchasing one of these telescopes because there are better options available which will be described later. If you are already in possession of one for what ever reason, then assuming a knowledge of objects to observe, described earlier, start observing using the following procedure.

Most High Street telescopes are provided with very limited finder telescope which can be no more than just a sighting tube. Even so it is best to align it if one is fitted. This should be done in the daylight on a distant object, say a telegraph pole. Do this by using the lowest power i.e. selecting the eyepiece with the longest focal length, marked on the eyepiece in millimetres, but without any Barlow x2 type tube if supplied. Through trial and error align the distant object in both the main telescope and the finder, this may not be easy since the mount may well be vibrating in the wind and the finder may have a poor focusing and adjustment mechanism, unfortunately this is symptomatic of this type of telescope. If no image is available at all, or is considered to be of very poor quality it may be that the telescope is out of collimation (mirrors or lenses out of alignment) or it suffers from some other fault, in which case it is advisable to obtain further information either from an experienced observer or publications available from the Library or from the Internet but don't give up without understanding why. Once an acceptable image is obtained in daylight then the adjustments should not be touched. Hopefully there will not be a long wait until the next clear night so the telescope can be put to use. Star testing a telescope on a clear steady night will show its true quality. Using a bright star try and bring the image to as small a point of light as possible with again the lowest magnification available. This may be tricky if the telescope does not have a substantial mount because it will wobble causing the star image to move wildly in the eyepiece, it may take several seconds to calm down until the telescope is next touched or blown by wind. Reflecting telescopes may require fine-tuning adjustments for optimum collimation which are best done on a star. If the best focus that can be obtained is an image that appears almost fan like and not small and circular this is a condition known as 'coma'. Hopefully the telescope has provision for adjusting the mirrors, normally three screws on the back of the mirror cells. Through patience, trial and error the coma can be reduced.

On a clear night, with perseverance interesting views of astronomical objects can be achieved. With 60mm refractors and 100mm reflectors you can view numerous lunar features, Jupiter's cloud belts and Galilean moons, Saturn and its rings, the phases of Venus, Mars with a hint of surface detail, M13 globular cluster in Hercules, M57 planetary Ring Nebula in Lyra, the colourful double star Albireo in Cygnus and the Trapezium stars of the Orion Nebula. There are lots of other objects that can be seen, but perseverance is required. As stated earlier we would not recommend purchasing one of these telescopes especially for the very expensive new prices, but if there is access to one then it may as well be used if their limitations are understood together with the reasonable expectations of the objects to be observed.

Even now we still haven't recommended a suitable telescope, but given an indication on ways to start observing. The best way to make a choice is to spend time researching the subject and the options available bearing in mind your own situation, i.e. location, space for storage, available money, motivation and particular astronomical interest for example.

Try to visit an astronomical society and ask questions. Here at the Lincoln Astronomical Society we have members who have good telescopes and have even constructed them. They are pleased to offer their accounts of using them and their experiences of using other telescopes. There are photographs and drawings of celestial objects displayed on the walls of the lecture hall that show what is achievable. The Society possesses its own telescope housed in a purpose built observatory. By using this telescope on dedicated supervised observing sessions a true expectation of what is achievable is obtained.

Study amateur observing accounts published in astronomical books, astronomical magazines and on the Internet. Library's now have Internet access. Perhaps e-mail those on the internet and ask for opinions. It can be seen by looking at the advertisements in magazines sold at the larger newsagents that there are various types and sizes of telescope available. Refractors, Reflectors, Schmidts, Maksutovs, and Cassegrains. All can be mounted either altazimuthly or equatorially. Prices can range from about £250 for a 6 inch Newtonian reflector (Dobsonian variety), to a few thousand pounds for computer controlled larger aperture models. Only by studying other peoples accounts of particular telescopes will it become apparent what is most suitable for ones own circumstances. It has long been said that for serious astronomical study that the minimum telescope that should be considered is either a 6 inch Newtonian reflector or a 3 inch refractor. Both these telescopes will certainly out perform the smaller types described earlier that are available from general camera shops. They can give pleasing views of many hundreds of astronomical objects (again, only if you have the correct expectations of the telescopes capabilities). An equatorially mounted version of either will cost more than a altazimuth equivalent. A sturdy equatorial mount is required if photography is to be contemplated, but these can be either manually or electric motor driven so as to keep pace with the apparent movement of the night sky. The cost goes up for every embellishment on the basic model. Second hand telescopes can reduce financial outlay and are available for various reasons, if one is seen advertised its potential capabilities should be considered before deciding if it suitable for personal requirements.

Consideration should be given to the possibility of making or modifying a telescope, there are books available that explain the various methods of doing so. In general there can be large cost savings by doing this and there is great satisfaction in viewing objects though a home built telescope.

It should be borne in mind that a telescope is not necessarily required by a keen amateur astronomer. For example, if you become a suitably competent and trustworthy member, then access to well equipped astronomical society telescopes is an option. Also some forms of astronomical observations do not require a telescope such as meteor shower observing.

Photography is a subject closely linked to astronomy, but a telescope is not always required. Some of the best amateur photographs have not required a telescope.

In conclusion we have not specifically recommended a particular type of telescope but would like to restate what are three important points to bare in mind when using any type of binocular or telescope be they of good or bad quality:

- Know were to find the astronomical object of interest.

- Understand the characteristics of the astronomical object to be observed.

- Be aware of the capabilities of the instrument chosen for the attempted observation.

It may be that the object is not seen at all, or hardly at all, but it will be understood why if these three points are remembered. In doing so your interest in observational astronomy will not wane.