To study and encourage popular interest in all branches of Science.

Newsletter May 2001

Dear Member,

Welcome to the true second millennium! Our last lecture meeting this session will be:

Thursday May 17th, Dr Christopher Walker (British Museum) on Numbers in Mesopotamia.

There will not be a July meeting this year.

ANNUAL GENERAL MEETING on Thursday June 21st at 8.15 pm.

This will start with wine and cheese (2 pp), followed by the AGM at 8.45 and then a Brains Trust, chaired by Martin Williams. Please submit your scientific questions in writing to him at the beginning of the evening or send them beforehand to him at 2, Highpoint, London N6 4BA or .

	Agenda for the Annual General Meeting.
	1. Minutes of AGM on 22nd June 2000.
	2. President's Remarks.
	3. Secretary's Report.
	4. Treasurer's Report.
	5. Proposal by Council to amend Rule 5b of the Constitution 
	   to reduce the number of ordinary members of Council 
	   from 8 to 6 and to reduce their service time 
	   from 5 to 4 years.
	6. Election of Officers and Council.
	7. Election of Auditors.
	8. Report of the Meteorological Section.
	9. Report of the Astronomy Section.
	10. Any other business.




Whenever a discussion arises on the possibility of life existing elsewhere in the Universe, it is often assumed that, if intelligent life does exist elsewhere, it must be far more advanced than we are. Furthermore, the fact that we have not been contacted by these advanced aliens, is taken as proof that our species is probably unique. We must surely realise by now that there is probably nothing unique about us, our Galaxy or our Solar System.

Not long ago it was assumed that life could not exist without an atmosphere containing oxygen. We now believe that this assumption was incorrect. When life began on Earth there was no oxygen in the atmosphere. It appears that water is the key to the development of life and there is no shortage of water in our Solar System. If our system is typical then water will exist in other systems as well and with it, life in some form or other.

It is how this life evolves which is open to question. It is not inevitable that life will evolve to produce species resembling Homo Sapiens. On our planet, the dinosaurs were the highest form of life for millions of years and may have continued to be so had not some chance accident in nature wiped them out. That chance event allowed evolution to take a different course, resulting in the evolution of mankind. It may prove to be the case that very intelligent species are very rare but even if that were true, in a universe composed of billions of galaxies there ought be millions of advanced civilisations.

So where are they all. Why the silence? One reason may be that it is not inevitable that an intelligent civilisation would necessarily develop an advanced technology. We only have to look at the history of past civilisations here on Earth to realise that many ancient civilisations developed to quite a high degree of sophistication without the recourse to technology. The ancient Chinese could predict eclipses without a telescope, they had a vast trading empire but did not invent the wheel. The ancient Egyptians built the pyramids without much mechanical assistance and other primitive civilisations explored the world's oceans without a compass.

Australian aboriginals have survived since the very dawn of time without recourse to any form of technology.

It may very well be the case that technological civilisations are destined for a very short life span. The development of technology produces terrible pollution and rapidly consumes the natural resources of the planet. We have only had advanced technology for a little over a hundred years. In that time we have cut down much of the tropical rain forest, caused damage to the ozone layer, greatly increased the quantity of greenhouse gases in the atmosphere - changing the climate and we have produced weapons of mass destruction - both mechanical and biological. Electrical generation by nuclear power produces dangerous radioactive waste which must be isolated for hundreds of years. We have introduced poisonous chemicals into the food chain from pesticides and fertilisers. Intensive farming has led to the rise of dangerous contaminants causing diseases like BSE and CJD. The indiscriminate use of anti-biotics fed to farm animals has caused harmful bacteria to become resistant to them. Unrestrained sexual practices have led to the spread of diseases like AIDS and there is compelling evidence that birth control drugs eliminated into the water supply are causing male sterility. Easy world wide travel allows the rapid spread of disease.

We are over fishing the oceans and contaminating them by the careless transportation of crude oil and other pollutants. We have caused the extinction of thousands of species of plants and animals and we are now about to begin genetically modifying those that are left.

The above are but a few examples of the potential dangers facing an advanced technological civilisation like our own, any of which could ultimately lead to its extinction long before it had time to communicate with a similar civilisation across the vast reaches of space. That is, of course, assuming that it is not terminated prematurely by impact from a comet or asteroid .

Second Thoughts on the Ages of Stars.

Peter R Wallis

For several decades there has been controversy over the age of the universe. Observation of the rate of expansion from the "red shift" suggest that it is 14 billion years old or younger; but observation of ancient stars found some of 15 billion years age! An interesting article in the May issue of the Scientific American (Rip van Twinkle by B C Chaboyer) now reports that, "The age crisis is over".

Till now, most astronomers have blamed the cosmologists for getting either the expansion rate or the cosmological model wrong but have been confident that their assessment of stellar ages was correct. The calculation age is based on our understanding of the nuclear reactions that power a star, essentially the fusion of hydrogen into helium. Four protons weigh 0.7 % more than a single helium nucleus, the missing fraction being converted into energy according to Einstein's equation E=mc2 .The sun emits 4 x 1026 watts of light and is therefore transmuting 600 million tons of hydrogen into 596 million tons of helium every second. Over a billion years the sun burns 1% of its mass. It is estimated that under normal circumstances only about 10% of the sun's mass in the core can reach the temperatures needed for fusion, giving the sun's life in this phase of 10 billion years, known as the "main sequence". When a star exhausts the hydrogen in its core, it progressively taps the gas in surrounding layers, causing the star to balloon into a "red giant" phase, so-called because of its higher luminosity but lower surface temperature.

In the stable main sequence phase it can be calculated from the laws of hydrostatic equilibrium, gas laws and laws of radiative heat transport that stars heavier than the sun will burn hydrogen at a faster rate. It is calculated that the luminosity varies as the 4th power of the mass; as the fuel available scales directly as the mass, the lifetime on the main sequence is approximately proportional to the inverse cube of the mass. This evolution shows clearly on the Hertzsprung-Russell diagram plotting visual brightness (indicative of energy output) against colour (related to surface temperature). Stars in their main sequence phase fall on a slanted line. When one becomes a red giant, it turns onto a near horizontal line.

Although we can estimate the total lifetime of a star from its absolute luminosity, the inherent stability of its main sequence phase means we cannot tell how old it is, how much of its life has been spent. It is only when it turns off the main sequence that its age begins to show. Astronomers therefore look at groups of stars which they judge to have been born at the same time. A special class of star groups, the globular clusters, are thought to include some of the oldest stars in our galaxy. They were first recognized as different by Walter Baade in the 1930s; he called them "Population 2" to distinguish them from the bright blue stars of "Population 1". The latter are bright blue - and therefore must be young - and are to be found only in the galactic disk. Population 2 stars are generally fainter and redder and are found in the galactic halo. Globular cluster stars are of the latter kind and this is also true of other galaxies near enough for us to see them.

We now understand why. The galactic disk is full of gas clouds, leading to lots of star formation and massive young flamboyant stars with short lives. They have significant quantities of elements higher than helium and lithium which can only have been formed in stars; supernovae produce the highest elements. The sun, for example, has about 2% by mass. The stars in a globular cluster have no more than trace quantities of higher elements and are now generally believed to be left over from the earliest days of our galaxy, before there had been sufficient novae to pollute space. They appear to have been formed at the same time and should be able to give an estimate of the age of the universe.

The heavier stars among them have all left the main sequence as red giants, the lighter stars are still there. This shows up on the Hertzsprung-Russell diagram as a sharp edge to the main sequence. Assessing their age depends on three factors: the proportion of higher elements, the accuracy of the modeling and the absolute luminosity of the stars. Chaboyer reports that recent measurements using the Keck Observatory have now determined the metal abundance with unprecedented precision. He and his colleagues claim also to have refined the modeling, reducing the estimated ages by 14%. The third problem was the assessment of the distances of these globular clusters, since distance must be known to convert relative luminosity into an absolute one, and this is still controversial. Chaboyer reports that the data from the ESA's Hipparcos satellite, which measures parallax to an accuracy of .001 arcseconds, has now pinned down the distance to similar metal-poor stars within the galactic disk, though it has not the accuracy to reach the globular clusters. Assuming however that these stars have a similar intrinsic luminosity, he claims that the distance to the globular clusters is perhaps 10% greater than thought previously. So they must be brighter, and therefore younger. He says that a best guess is that the oldest stars are 13 billion years old - consistent at last with the age of the universe from red shift measurements. New orbiting observatories are scheduled for launch later this decade and, with 250 times the resolution of Hipparcos, they should be able to resolve some of the remaining uncertainty.

But perhaps we should be careful, as there are arguments about whether the expansion of the universe is accelerating. This would allow its age to be greater.

Healthy Milk?

Some of you may not have seen the report by Miranda Ingram in the Times about the work of Dr Corran McLachlan into links between heart disease and the type of cows' milk that we drink. He is a New Zealander with a degree in chemical engineering from Cambridge and runs a company there producing cholesterol-free dairy products. It has been known for some time that the risk from heart disease varies considerably from country to country. Dr McLachlan believes that the protein in cows' milk explains the differences. The protein is largely made up of caseins, beta casein A1 and A2. He says that if your body has been compromised by smoking, fats etc, A1 could be fatal while A2 is safe. He claims that the proportions of the two types of casein in the cows' milk correlates with the observed risk. Finland, for example, consumes the highest amount of A1 and has the highest heart-disease rates in the world. Guernsey cows produce almost exclusively A2 milk and deaths from heart attacks are 27% lower there.

He claims that intensive breeding in westernized countries has led to the production of A1, and that careful selection of bulls and females could achieve its elimination; indeed he suggests that the cull rates and controls occurring in Britain to counter BSE and Foot and Mouth disease would allow it to be eliminated in 3 years at very little cost.

While there is interest amongst UK trade bodies, eg the Dairy Council and NFU, there is also suspicion, since McLachlan runs a company, A2 Productions, and holds the licence for the A1/A2 screening process. Miranda Ingram suggests that the milk sellers could well be forced to act if supermarkets decide that customers want it.


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Last updated by Julie Atkinson   28-Jan-2018