The comet is named after the British astronomer, Edmund Halley (1656-1742) who observed it in 1682. He predicted accurately that it would return in 1758, but died too soon to see it. Halley’s Comet has a period of 76 years and was last seen in 1910, when this photograph was taken.

     Comets have been called the stray members of the solar system, but the description is misleading as a comet’s orbit can be calculated like that of a planet, though they may appear unexpectedly.

     A comet is formed of relatively small particles contained in an envelope of thin gas. A large comet has a concentrated head or nucleus, from which streams a long, brilliant tail, but a small one may have no tail. Although a comet may be larger than the earth of even Jupiter, it contains only a small quantity of matter. This lack of substance makes it invisible until relatively close to the earth.

     A comet’s tail always points away from the sun, probably because of the intense radiation, which repels that tail’s tiny particles. Its orbit is much more elliptical than that of a planet, and, because they are so insubstantial, they can be seen only when relatively near the Earth.

     Their crater hollows are found all over the world. A meteorite, which probably weighed hundreds of tons, is believed to have fallen near Winslow, Arizona, in the United States several thousand years ago. The Barringer crater, as it is known, is about one mile across and over 500 feet deep. Another large meteorite is known to have fallen at Grootfontein in South-West Africa. This weighed about 60 tons. An iron meteorite in New York City, which was brought from Greenland, weighs 36 tons.

     Light rays are reflected and absorbed by opaque materials such as iron, lead and rubber. Transparent materials, such as glass, air, water, oil and certain plastics, allow the light rays to pass through them. But in doing so they bend them to a greater or lesser degree.

     Refraction occurs in nature. The stars not directly overhead are in different positions from those they appear to be in, because the light rays from them are refracted by the earth’s atmosphere. Desert travellers sometimes see mirages, which are caused by refraction through the atmosphere.

     The moment you put a match to the wick, you start a change in the candle by turning the solid wax into a liquid. The liquid wax rises to the wick by an irresistible process called capillarity, the simplest example of which is the way blotting paper soaks up ink or water. Then the liquid wax changes into a gas which burns-a chemical reaction which releases energy in the form of light and heat.

     The presence of the gas can be demonstrated by blowing out the candle and immediately holding a lighted match an inch or so above the wick. The inflammable vapour instantly catches fire and the candlelights up again without the match having actually touched the wick.

     Other changes are taking place while the candle burns. The wax is a complex chemical compound of carbon and hydrogen. The process of burning is simply the combination of the wax with the oxygen in the air. If you put a jar over the candle, it will quickly use up the oxygen and go out.

     During the time the candle burns the carbon joins with the oxygen in the air and makes carbon monoxide and carbon dioxide, and the hydrogen combines with the oxygen to produce water.

     While all these changes in the substance of the candle are taking place, the candle, of course, is becoming shorter. But it is not "going" anywhere. Its materials are simply changing into other substances.

     During regular 11-year cycles, the number of sunspots may increase to as many as 100. The sunspot cycles coincide with a build-up of solar violence, but scientists are not yet certain what causes these disturbances.

     Observers should remember that it is dangerous to gaze directly at the sun without protecting the eyes with a densely smoked special glass.