When light falls on a surface some of the light may be reflected or thrown back, some absorbed and some allowed to pass through. In a mirror the surface is made so bright that as much light as possible is reflected and as little as possible absorbed.

     The earliest mirrors consisted of thin discs of metal, generally bronze, slightly convex and polished on one side.

     The method of making mirrors by backing glass with thin sheets of metal was known in the Middle Ages, and a guild of glass-mirror makers existed in Nürnberg, Germany, in 1373. The commercial manufacture of mirrors was developed in 16th Century Venice. Coated mirrors were made from blown cylinders of glass, which were slit, flattened on a stone, polished, and their backs silvered by an amalgam of tin and mercury.

     These mirrors had a high reflecting power, but a considerable improvement came in France in 1691 when the art of making plate glass was introduced. Baron Justus Von Liebig of Germany discovered the chemical process of coating a glass surface with metallic silver in 1835.

     Mirror surfaces are used inside lighthouses, lightships and searchlights, where it is necessary to produce a high degree of reflection in order to throw the beam of the light over a distance of several miles. Even a hand flashlight has a slightly mirrored surface behind the bulb.

     Modern astronomers think that many millions of years ago there was a huge explosion in space. The do not know exactly what happened. But is possible that our sun exploded or that a much bigger communion star of the sun became a supernova that is it broke up violently. The debris and blazing gases from this explosion were, it is thought, flung far into space.

     For more millions of years our universe boiled and bubbled. But slowly, very slowly, the fiery redness began to cool and condense into the nine planets and many more smaller bodies. All these planets now revolve around the sun.

     After further vast periods of time the lava of the earth began to solidify, developing over many millions of years, into the world, as we know it today.

     A shadow is that part of an illuminated surface, which is shielded from oncoming light, rays by an object through which the light cannot pass. If the source of light is small, the outline of the shadow will be sharp and pronounced and its shape will be that of the object producing. If the source of light is large, the shadow is very dark in the middle (the umbra) and much lighter on the outside with indistinct outlines (the penumbra).

     Shadows cast by the sun always have a penumbra and the shape of the shadows cast varies with the position of the sun in the sky and the angle of its rays. An upright pole will cast a long shadow in the morning when the sun is rising but grows shorter as noon approaches. As the sun declines in the sky, the shadow grows longer again.

     Human shadows have often had a mystical or magical significance. In the picture above you can see a masterly use of shadow of give form by the English painter Wright, of Derby.

     By using a combination of two mirrors at right angles to each other, the reversal will be eliminated. This is because the reversed image will be reversed yet again in the second mirror, thus giving a true likeness of the original object.

     These conditions can be reproduced in a large spacecraft or space station in orbit, but an astronaut still needs a space suit for operations outside the craft or for an emergency.

     In space men lack the air needed for breathing, the pressure required to stop their blood from boiling and the natural protection of the atmosphere against radiation. All these must be supplied by the space suit, which also must withstand the cold of space.

     When astronaut ventures into space, he leaves behind the safety of the atmospheric blanket which we, on earth, take for granted. His space suit becomes his own personal little world.