Scientific World: Is anyone there? (Part three)

FRANK WILLIS YOUNG SOCIALISTS CANDIDATE CENTRN COMMITTEE ROOMS T ADES DAILY NS police state lau. 'IF THERE are billions of stars, chances are there must be intelligent life somewhere in the galaxy?

This argument is often used to 'substantiate' the contention that other civilizations exist elsewhere in the universe and was, indeed, almost the only basis on which the PAGE THREE SCIENTIFIC WORLD our sun.

IN PAPER MEET TRALIA astronomers of antiquity could argue.

To a large extent, present theories concerning the origin of life on earth give some substance to these probabilistic arguments.

Today, it is largely accepted that the formation of terrestrial life was a process that started with the mixing of non-living chemicals in a primeval 'soup' millions of years ago and which 'by chance' gave rise to the simplest molecular structures, which could develop at the expense of the environment.

rumenter silly one the argument life on other worlds on the laws of probability not very helpful. We have to know where to look and even a cursory glance at the night sky reveals to the naked eye millions of stars from which to choose for our examination.

Astronomical observation, particularly with the use the radio-telescope, has given us a fairly detailed picture of there?

On this scale, the distances involved are so immense that it is necessary to deal in lightyears rather than miles.

As light travels about six million million miles in 1 year, we can begin to grasp the smallness of our own solar system and the immense distances over which our instruments pick up their signals.

The our nearest extra-terrestrial neighbour, is a mere one-and-a-third lightseconds away, while a meagre eight light-minutes separate us from the nearest star, our own sun.

At the speed of light you can be out of the solar system in five hours, a journey which will take our own rockets around ten years at the pre sent level. o. technology.

The nearest star which lies outside our solar system, but which is not visible from the northern hemisphere, is Proxima Centauri, and at a distance of 4.2 light-years (l.y.) it is about a million times further away than the nearest planet.

UNIFORM

The stars themselves do not form a uniform pattern in the sky. On a clear night, the Milky Way—a great belt of mainly faint stars - stretches from one horizon to another and, in fact, divides the sky into two equal halves.

It has been concluded that our sun is part of a system of around 200 billion stars— the galaxy-which is shaped like a discus.

This disc is about 20,000 1.y. across and 1,000 l.y. thick and when we look at the Milky Way, we are seeing the galaxy 'edge on', so that stars seem to pile up along a narrow band of the sky.

It has been calculated that our sun is very close to the central plane of the galaxy and about half-way from its centre to the rim.

To find any substantial concentration of matter outside our own galaxy, we will have to travel a distance of 14 million I.y. until we reach yet another galaxy.

In fact, galaxies--sometimes called 'island universes'— appear at fairly regular intervals in space at approximately this distance between neighbours.

However, the picture is not one that can be exhausted simply by thinking of millions of billiard balls clustered in various regions of space and interacting through gravity.

The 'gaps' between the stars and the galaxies contain regions of gas as well as 'matter' in the form of radiation fields.

In fact, it is the radiation that we receive from the stars that yields the majority of man's information about them.

Ordinary daylight is made up of light waves of many different wavelengths. When we think of waves, we may think of water waves where the wavelengths-distance between crests—are measured in feet.

However, when we are dealing with light, or any radiation, we are dealing with distances which are measured in millionths of a centimetre and the usual unit of length is taken as one Angstrom (IA) which is a hundred millionth of a centimetre.

Visible light, which can be detected by the eye or an optical telescope, comprises wavelengths that lie between 4,000A and 7,000A, corresponding to deep violet and deep red respectively.

Wavelengths below 4,000A are in the ultra-violet region of the spectrum (that is, the complete range of wavelengths); below about 100A, in the x-ray region; and below 1A, in the gamma-ray region.

As we can see, the shorter the wavelength, the more penetrating is the radiation.

Wavelengths longer than 7,000A give rise to the phenomenon of heat and therefore infra-red radiation is also called heat radiation.

WAVELENGTHS

Moving to still higher wavelengths, we pass into the region radio waves where, on 'long wave', , we deal with wavelengths of hundreds of metres.

Radio telescopes receive and register radiation over a much wider range than optical telescopes and therefore can amass a vast amount of information.

Sometimes the flow of radio radiation may exceed by many times the flow of visible radiation in terms of energy output. Such a case is the galaxy Cygnus A. In terms of visible radiation, the galaxy appears as two insignificant specks of light in our most powerful telescopes.

Actually the absolute output of visible light is very great —about ten -times our own galaxy-but the 'faintness' is due to the immense 600 million l.y. gap between us.

Yet the flow of radio radiation reaching us from Cygnus A in meter wavelengths is so great that it exceeds that from the sun during periods of low sun-spot activity!

The spiral galaxy M104 In the constellation Virgo.

This galaxy is oriented so that we can see It edge-on. bright against a darker background.

It is fortunate that this tremendous outpour The alone composition of the stars. • iato is diferent dom split glass prism. of us the formation or a rainbow where droplets take the laboratory prism.

• une lient tror a star a prism, we also get a rainbow, but a rain. bow in which certain are missing.

This iS because each chemical presen the star has part with a parWe may terms of soldiers marching across a bridge. If they march at a particular pace, resonance ar waveradiation they and this tells him the elemthat present withi the star itself.

lines' are of the spectrum corresponding to hydrogen helium, solium, calcium and potassium.

Hydrogen and helium are the principal constituents of almost stars, while the others are present in relatively minor quantities.

SPECTRA

Not only do stellar spectra tell us the chemical composition of stars, but also their speed away from us and their velocity of rotation.

This is because of the Doppler effect, and is fairly commonplace when dealing with sound waves. If we stand by a railway line and listen to the whistle of a fast train as it passes us, we experience this ect.

pitch of the whistle to drop as the train the source away, are increased. If • Source as star - approaches are decreased are dis placed the blue of the spectrum.

If ing, are increased and the lines shift towa the red end of the spectrum.

When a star rotates, part of its surface is moving towards us and part away from us and this is recorded in its

The chemical composition of a star has an obvious relevance if we can assume that these elements will also be present in its planetary system Gif any). This is because we know that certain elements are necessary as the basis for life as we can imagine it.

However, the relevance of the speed of rotation of the star is not so obvious until we examine the possible theories of the origin of our own solar • To be continued