This edited article about the moon originally appeared in Look and Learn issue number 700 published on 14 June 1975.

The earth seen from the moon

When you spin a top you give it a smart twist to start it going and then leave it alone.

It is exactly the same with the Earth. It was given its spin when it was formed, 4,500 million years ago, and it turns today only because it has not yet come to a stop.

To see how it spins we must find out how the Earth was made.

One theory is that the Earth came from a vast cloud of tiny particles of rock and metals, all circling round the Sun in separate orbits.

Presently some of the particles jostled against each other and stuck together, and the lump began to grow like a snowball, gathering more and more particles until it became a large, solid ball – the Earth.

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This edited article about supernovae originally appeared in Look and Learn issue number 692 published on 19 April 1975.

An imaginary depiction of our own sun exploding as it dies by Michael Whittlesea

In 1054 China was locked in one of her many bitter wars with the Tartars. So the emperor ordered his astrologers to see if the stars could forecast a victory for him.

One night, while the astrologers were scanning the night sky, they saw the bright light of a star that had not been there before.

Night after night, for several months, the new star shone brightly. Then it gradually dimmed until it became an ordinary star like thousands of its neighbours.

History does not tell us whether or not the Chinese astrologers took the new star as an omen of victory over the Tartars. But the astrologers had made astronomy history by discovering the first recorded example of what is called a supernova.

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This edited article about the Northern lights originally appeared in Look and Learn issue number 682 published on 8 February 1975.

Eskimos watch the aurora borealis or northern lights by Ron Embleton

If you are very lucky you may sometimes see a dazzling display of coloured lights in the sky at night.

These are the southern and northern lights which flash across the sky in the form of brightly-lit arcs and are constantly in motion.

Sometimes these brilliant rays of light will ‘dance’ up and down in the sky and these are called the Merry Dancers. At other times, rays will spread out and upwards in the shape of a fan or flash out in different parts of the sky rather like huge searchlights.

From a great distance from the equator, north and south, the lights often look like enormous burning draperies hanging from the sky and coloured flames moving up and down in layers.

These displays of light are called aurora by scientists. The northern lights, which are seen in the northern hemisphere, are called aurora borealis, and the southern lights which are seen in the southern hemisphere, are called aurora australis.

In the northern hemisphere the aurora is seen at its best in northern Scotland, in northern Sweden and Norway and around the Hudson Bay region of Canada.

These displays of light are caused by gigantic eruptions, called flares, which take place on the Sun. During a flare, millions of small particles, believed by scientists to be protons, are sent out by the Sun. By travelling at about 1,000 miles per second, the particles reach the Earth twenty four hours later. They are caught by the magnetism of the Earth and move rapidly down through the air. As they travel down they collide with the atoms and molecules of the air, and these collisions send out light. It is this light which is seen in the sky and which produces the amazing display of colour, which we call aurora.

This edited article about the universe originally appeared in Look and Learn issue number 676 published on 28 December 1974.

Radio astronomer

Big things were happening at the top of a mountain in California, U.S.A. Through a 100-inch telescope installed there, Edwin Hubble was exploring the universe beyond the solar system, beyond even the vast belt of billions of stars called the Galaxy, of which the solar system is a part.

As he searched the heavens, Hubble saw other galaxies, each containing billions of stars. They were so far away that they looked like patches of mist. Some were shapeless masses, others looked like spiralling Catherine wheels (like the Milky Way above) and others were lens shaped, like the picture on the left.

But the amazing thing was that each of these galaxies was opening out and moving farther and farther away from us. The most distant galaxies were travelling faster than the nearer ones.

Hubble was able to tell this because he had, as an assistant, Milton Humason, who spent hours taking photographs of the light given off by these galaxies. Last week we explained that a spectrum is the band of coloured light into which white light is changed when it is passed through a prism. Some of the galaxies were so faint, that Humason had to expose his photographic plate for 70 hours in order to make a photograph of them.

The photographs Humason took showed that dark lines crossed the spectra. The closer these were to the red end of the spectrum, the more distant was the galaxy. By their study of these photographs, Hubble and Humason were able to tell that all of the galaxies were moving farther and farther away from us and that the universe really was expanding.

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This edited article about space originally appeared in Look and Learn issue number 671 published on 23 November 1974.

A cut-away image of the sun by Harry Green

Scientists aboard an American laboratory floating in space, called Skylab, had a very important job to do. They had to find out all they could about the vast, flaming mass of gas that we call the sun. For more than eight months they worked at their instruments, recording the heat at various parts of the sun, the intensity of the light and the extent of the sun’s halo.

If you look at the cut-out picture, you will see some of the things they either discovered or confirmed. This shows you how the sun produces a variety of rays and different intensities of heat. After the core, which is unimaginably hot, there are various layers of heat. Then we come to the outer edge from which spectacular flares shoot off. Forming the sun’s outer atmosphere is the corona which, although it can only be seen near the edge of the sun, extends for many millions of miles.

The sun is the centre of the solar system. Nine planets or worlds (of which Earth is one) revolve around the sun. For thousands of years, men have been looking at the sky and trying to learn about this strange solar system.

The first of the great astronomers to study it was Greek. He was Thales of Miletus who lived from 624 to 546 B.C. He is thought to have been the first person to have stated that the Earth is a globe. Aristotle, a Greek philosopher of 385 to 325 B.C. found a way of demonstrating this. He said that the Earth’s shadow, when it was seen on the Moon during an eclipse, was curved and indicated that the Earth was round.

For a long time, people thought that the sun and the planets went round the Earth. Ptolemy, Egypt’s royal astronomer in the second century A.D. put forward this theory, which was believed for more than 1,300 years. In 1543, it was challenged by a Polish priest, Copernicus, who said that the Earth and Mars went round the sun.

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This edited article about the Northern Lights originally appeared in Look and Learn issue number 875 published on 21 October 1978.

Eskimos watch the Northern Lights by Ron Embleton

If you go to Scotland for a holiday, you might well see the Northern Lights – a coloured band across the sky that can be seen only when it is dark or at twilight.

Unlike a rainbow, however, the Northern Lights do not take the form of a narrow arc; rather, they look more like an illuminated curtain hanging from the sky. They are an extremely beautiful sight, and can change colour and shape very quickly.

The real name for these lights is Aurora Polaris, which means “polar light”, since they can only be seen at high latitudes. The further north or south of the equator you are, the more likely you are to see them. This is why they can be seen more easily in northern Scotland than in England.

Polar light can be seen at both ends of the Earth, and in the North is called Aurora Borealis (Northern light), and in the South, Aurora Australis (Southern light). It seems most likely that the effect is due to electrically-charged particles emitted by the sun passing through the Earth’s atmosphere.

These particles travel at great speed – hundreds, perhaps thousands of kilometres per second – and as they enter the Earth’s atmosphere, they are moving so fast that they cause the molecules of the air to glow.

But why should they only be seen around the Earth’s two poles? The answer to this question lies in the Earth’s magnetism, which is greater at the poles than at its widest part. As the particles enter the atmosphere, they are attracted to the centres of magnetism, which occur at the ends of the Earth’s axis.

This edited article about astronomy originally appeared in Look and Learn issue number 874 published on 14 October 1978.

Mariners being guided by the Southern Cross

Would you know how to find your bearings if you were lost in a boat somewhere near the South Pole? You would if you knew where the Southern Cross was.

The Southern Cross is the name given to a constellation, or group of stars, lying near the southern celestial pole, which is part of the sky directly over the South Pole. There is no mystery behind the constellation’s name – it is simply due to the fact that the four stars which make it up seem to form the points of a cross.

Mariners have always reckoned by the Southern Cross because the vertical section of the “cross” points almost exactly to the southern celestial pole, which is unmarked by any other bright stars.

This edited article about astronomy originally appeared in Look and Learn issue number 869 published on 9 September 1978.

Sir William Herschel by John Cameron

One evening in 1781, William Herschel was peering through his home-made telescope, unaware that during the evening he was to make a discovery that would change his life.

He saw an unfamiliar round object passing through the sky and, after fellow astronomers had plotted the orbit of his sighting, it was found that Herschel had discovered a new planet – Uranus.

This brought many rewards, including an important medal and a Fellowship of the Royal Society. In 1782, he was appointed private astronomer to George III. Soon, honours were being showered on him by British and foreign universities and scientific societies for his brilliant astronomical researches.

This edited article about archaeology originally appeared in Look and Learn issue number 823 published on 22 October 1977.

The building of the Great Pyramid at Giza, by Harry Green

The native porters who accompanied Flinders Petrie to the Pyramids of Giza might well have been excused if they had believed they were escorting one of those eccentric Englishmen who were roaming around Egypt in the latter part of the 19th century. Certainly, his behaviour seemed highly irrational. On reaching the site, instead of making his home in a tent, Petrie took occupation of an abandoned mastaba, a type of interment chamber, where he installed a kerosene cookstove, a chair and a box which was to serve as a table and a place on which he could place a lamp while he worked on his notes.

If the porters could not understand why Petrie had chosen the privacy of the mastaba as his home, they were even more puzzled when they saw him emerge from it on the first night, naked, with a lamp in one hand and writing equipment in the other. Ignoring the porters completely, he stumbled over the rocks towards the mass of stone rising up against the star-stewn sky. With the aid of the lamp, he found the entrance to the pyramid and disappeared inside.

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This edited article about the Solar System originally appeared in Look and Learn issue number 1047 published on 3 April 1982.

Cutaway picture of the sun showing the core, chromosphere, photosphere, sunspots, polar plumes and corona, by Harry Green

The Sun is a very ordinary star, similar to billions of others scattered across the Milky Way. An island of stars in space, the disc-shaped Milky Way is a galaxy so broad that light takes 100,000 years to cross it. This galaxy is much older than our Sun, which is a relatively young star, checking in at a mere 4.5 billion years.

The earliest stars that formed contained only hydrogen and helium – the raw materials of the galaxies. All other elements have been made inside stars, by a process known as “stellar nucleosynthesis”; at stars’ cores, simple elements like hydrogen and helium are literally fused into the heavier elements. This nuclear fusion is what drives the stars, their energy being released in line with Albert Einstein’s famous equation E=mc2 (in which E is energy, m is mass, and c is the speed of light). The elements produced include those we on Earth regard as commonplace, such as the carbon and oxygen so important to living things.
When old stars die they may explode and scatter the heavier elements across space, so that they are mixed, in tiny proportions, into the clouds of gas from which new stars form. From these new stars, an even smaller fraction of the heavy elements can settle out in the form of rocky planets like the Earth. In fact, everything on Earth except the hydrogen in water and the rare gas helium, has been made inside stars – we are, literally, stardust.

The Sun contains 99.9 per cent of all the material in the Solar System, and all but two per cent of this is hydrogen and helium. And within the innermost quarter of the Sun’s radius – only about 1.5 per cent of its total volume – half the mass is concentrated and 99 per cent of the energy is generated.

Nuclear fusion goes on only in the heart of the Sun. At the centre the temperature is about 15,000,000 degrees C, and a little bit higher just off-centre in the main nuclear fusion region. It then falls off dramatically to the visible surface which has a temperature of “only” 6,000 degrees C!

The fusion process involves the conversion of hydrogen into helium; eventually ail the hydrogen will be used up and nucleosynthesis will convert helium into carbon; but this will not happen for another five billion years.

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