Telescopes

The stars, remote and sparkling like diamonds on a velvet background, have fascinated man since the beginning of time. Sailors charted their paths by them, poets reveled in their beauty and there's hardly a popular song that doesn't bring them in at some point.

As you look up at the sky on a clear night it seems as though you are standing under a slowly-rotating dome, dotted with twinkling lights. In reality, however, it is the Earth which rotates on its axis and which gives the impression that the stars are moving. The North Pole always points towards the North (or Pole) Star. This is why this star always remains in the same place in the sky and is so very useful as a guide in plotting courses.

A pair of ordinary field glasses is a great help in observing the sky at night. On a clear night, with the naked eye, one can see up to about 2,000 stars. With a simple telescope, hundreds of thousands come into our view though, in our Galaxy alone; there are probably more than 100,000 million stars.

Alpha Centaurus, the star nearest to us, is just over four light-years away. A light-year is the distance traveled by a ray of light, moving at a speed of 186,000 miles each second, in the space of one year. This means that an explosion on that star would not be seen by us until over four years after it actually happened!

Astronomy is not only a fascinating science but also a field in which many amateurs have become famous. Every year an average of 15 comets are reported. Some of these are discovered by amateurs and will bear their names for all time.

The invention of the first simple telescope by Galileo Galilei in 1609 was a major step forward in understanding the Universe in which we live. Today, with the conquest of space in progress, we know more about the Universe than seemed possible even 25 years ago, though there are still hosts of unanswered questions.

Modern sophisticated equipment can make visible impulses of light six million times weaker than those detected with the naked eye. The most powerful optical telescopes, built with parabolic mirrors, are used in observatories throughout the world. The largest of these is in the United States at Mount Palomar Observatory, near San Diego. There are, however, other types of telescopes, eg radio telescopes, which can pick up signals from the stars in the radio wavelengths.

Stars are graded according to their brightness. The higher the grade, the weaker is the strength of the light received. For example, the stars in the constellation of the Little Bear are all regarded as second, third, fourth and fifth grade (magnitude) stars.

A keen amateur astronomer can build his own telescope without too much difficulty. You can buy loose telescope lenses to use in building your own or purchase a complete kit to assemble yourself. These come in different price ranges.

Building a telescope
Two tubes are required, about 100cm (40in) long, with different diameters able to accommodate the lenses to be used. The tubes can be made of cardboard, metal or plastic. Whichever material, they will need to be painted on the inside with a black matt paint, to avoid reflection of light. This is best done with a spray.

The lenses are then glued to small pieces of strong cardboard, or plywood, and fitted inside the tubes. Fix plywood rings to the section of the smaller tube, which fits inside the larger one, so that it can be moved the required distance.

The best telescope is only as good as its stand. It is essential to keep it steady yet be able to move it freely and to focus it clearly. The diagram provides a clear visual breakdown of how the tripod is made. Start by finding the centre of gravity of the fully extended telescope (the spot where it balances when supported). Mark the spot. Then cut two blocks of wood, large enough to take in half the circumference of the telescope. A piece of metal forming a U with squared off corners is fixed to the wood blocks with a wing nut which holds the telescope in position. The whole thing is then screwed on to a tripod so that the telescope can be moved at will, and then screwed into the required position at the top of the tripod.

More expensive telescopes have a complete set of lenses instead of just two and, of course, a telescope as simple as the one described cannot be extended too much without causing distortion. However, you can have fun with your telescope and perhaps make interesting observations.

Finding your way around the sky
First of all find the North Star. This will always be in the same position in the sky each night. If you are a beginner, you might find a celestial globe easier to use than trying to follow a flat star map. When working with maps and looking through the telescope, use a torch with a dimmed red light to read the map; a sharp white light will provide too much glare and prevent you from seeing through the telescope for a few minutes.

The Moon, Venus, Jupiter and Saturn may be seen in great detail. Comets are also most interesting, particularly if they show tails, which consist of small particles of gases extening out for hundreds of thousands of miles.

Equally fascinating, though best seen with the naked eye, are meteors (shooting stars) and the Northern Lights (Aurora Borealis).

Once you become involved in astronomy, you will realize that it is more than a hobby. There are many ways of broadening your knowledge from now on, through professional journals, books of all standards and through many local societies or associations.