Practical Astronomyby Storm Dunlop
A well illustrated basic introduction to practical observational astronomy designed for beginners. Includes star charts, instructions for planispheres, as well as coverage of astronomical objects, images from the Hubble Telescope and more.
Stuart J. Goldman
- Firefly Books, Limited
- Publication date:
- Product dimensions:
- 5.00(w) x 7.75(h) x (d)
Read an Excerpt
Astronomy is a fascinating hobby that anyone can follow. You do not need to be -- as some people seem to imagine -- "mathematically minded" to start, or even to become a very experienced observer. Yet astronomy is one of the few hobbies where not only can you gain great enjoyment, but if you want to, you can very easily make observations of great scientific value.
What is perhaps even more surprising is that you do not need complicated equipment -- or indeed any equipment at all. So if you are a beginner, do not feel that you must rush out and buy the most expensive telescope that you can afford. This could be a big mistake, as it might prove to be completely unsuitable for the objects which you later find are most interesting. If you must buy anything, a pair of binoculars is certainly far more useful at first, but even these are not essential, and some of the things that may be observed with the naked eye are described on page 20. Similar lists of objects and observations that you can make with binoculars and telescopes are given on pages 54 and 55, while details of how to choose (and test) binoculars and telescopes are also given later.
Because this book is intended for amateurs who are just starting to make practical observations, it does not attempt to discuss the equipment or methods used in some of the more specialized fields of study, including some where highly experienced amateurs are making major contributions to astronomical science. Some of these areas are mentioned, and some examples of results are included in the images that are shown, but for detailed discussion the reader is referred to the various sources (such as books, Internet sites and societies) listed at the end of this work.
How to use this book
There is such a range of objects in the sky that there is always something to see, from meteors and auroræ in the Earth's atmosphere, to more distant planets and stars, and extending out to remote galaxies far off in space. There is a lot of pleasure to be gained from "rambling" around the sky, looking at whatever objects happen to be available at the time, or which take your fancy. Everyone has to start by learning to find their way around, and by recognizing the different constellations. This is the way that this book begins, as well as by giving general information on how to set about observing.
After a while, most astronomers find that they become particularly interested in a few classes of objects, on which they tend to concentrate their attention. Because these may require different types of equipment, or different methods of observation, they are individually described in the various chapters later in this book.
Beginners often find it a bit confusing because there are so many different objects, each of which is best observed in a particular way. Similarly, when first starting it is not always easy to know what may be seen or studied with particular equipment. A number of flow charts and tables have therefore been given, which should help you to find the relevant sections where the different subjects are discussed, and to move on to the next stage in discovering the fascination of astronomy.
Starting to observe
There are a few things to remember when you start to observe, but first make sure that you are warm and dry -- no-one can observe properly if they are uncomfortable. Even in summer it may get quite cold at night, so wear plenty of clothing. A quarter of all body heat is lost through the head, so a hat is often essential. Dampness (especially underfoot) makes the problem of keeping warm much worse, so a dry site is better than standing on wet grass. Stone and concrete may become very cold, and hard to the feet during a long observing session, so wooden duckboards which provide some insulation are ideal.
Try to pick a spot that also offers some protection from the wind, not only because it will be warmer, but also because the wind can shake binoculars or telescope, making viewing more difficult. Even a simple windbreak can help a lot. Dampness as it affects equipment is discussed later in this chapter. Observers in warmer locations have other problems and may find that mosquito repellant is an essential part of their equipment.
The eyepieces of many telescopes can assume awkward positions and heights at times, so you may need some form of steps. These must be sturdy and stable, but reasonably easy to move. A stout wooden box may be a satisfactory alternative. Diagonals can help to make the eyepiece more accessible, but they introduce a mirror-image reversal, which means that the view may be difficult to compare with charts or photographs. Looking high overhead is easier if you use a reclining, garden chair (preferably one with arms) rather than craning your neck -- and it is also far more comfortable. Some observers like to lie flat on the ground on a sheet of thick foam or an airbed.
It also helps to have everything to hand. Some telescope tripods incorporate space for small items such as eyepieces, but a garden table is more suitable for all the bits and pieces that you may want.
The pupil of the eye responds almost instantaneously to major changes in light by expanding or contracting, but true dark adaptation takes place when a pigment (known as "visual purple") builds up inside the retina. This takes about 30 minutes or more, during which time the eyes slowly become more sensitive. It helps if the eyes are protected from bright lights before you go out to observe -- some observers even wear sunglasses before starting an observing session. There are strong indications that dark adaptation becomes better and faster (within limits) the more frequently it is used, and this is another argument for trying to observe as often as possible.
Bright light quickly destroys dark adaptation at any time -- even viewing the Moon through a telescope will do this -- but a very dim red light has least effect, so make sure that you have one for examining charts and writing notes. Cover a suitable lamp or pen-light with red paper or plastic, and either change the bulb to a dimmer one, or make sure that the covering lets through only a weak light. When fully dark adapted, and under a clear sky, there is a surprising amount of light from the stars alone, often more than enough to enable you to move around without too much difficulty.
The advantage of binocular observing is that you use both eyes at once, in the normal relaxed manner. With a telescope, try to conquer the natural tendency to close the "unwanted" eye, because this only leads to strain on both. With practice one eye can be "ignored," but if this proves too difficult, or if there is a lot of stray light causing interference, wear an eyepatch that allows you to keep both eyes open.
The most troublesome eyesight defect is astigmatism, which can cause stellar images to appear elongated or misshapen. Long- or shortsight does not pose many problems, because most binoculars and telescopes have sufficient range of focusing adjustment for this to be accommodated. If spectacles have to be worn all the time, take particular care in selecting equipment. Some suggestions about this are given later.
At first most beginners wonder if there is something wrong with their eyesight when they cannot see faint planetary detail, or pick out the dimmer stars. But it is surprising how quickly one's perception improves with practice, so the more frequently you can observe the better. Experienced observers frequently use averted vision -- looking slightly to one side of the faint object they want to see, so that the image falls on a more sensitive part of the retina. This does work, although exact positions may become a little more difficult to judge. Although telescopes and binoculars should be as rigid as possible, tapping the eyepiece very lightly may sometimes bring faint stars into view, because the eye is
Meet the Author
Storm Dunlop is a well-known authority on astronomy and meteorology. He is a Fellow of both the Royal Astronomical Society and the Royal Meteorological Society, and the photography editor of the Journal Weather. He is also past president of the British Astronomical Association and lectures on all aspects of meteorology and astronomy.
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