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ASTRONOMY/HERSCHEL A Second Astronomical Miscellany Friday 2 January 2004As a result of the popularity of the ‘Astronomical Miscellany’ of June 2003, it was decided to invite three of our regular members to present a twenty-minute talk. Two members offered a talk on the same subject, so they collaborated with each other and shared the time.
The Search for Extraterrestrial Life - Dave Ladbrook and Dr. Steve KimminsDave outlined the properties needed for life (the ability to store and replicate molecular information and the presence, or potential for, enzyme catalysis) before sketching the four philosophical arguments regarding the origins of life. Miller and Urey's famous 1953 experiments were mentioned, as was the December 2003 Royal Society meeting on 'Life Without Water'. It was noted that life effects massive atmospheric changes (as seen over geological periods on Earth). As a consequence of biotic activity, Earth's atmosphere is far from chemical equilibrium. Life also exhibits homoeostasis. Tables were shown illustrating the huge differences between the air/oceans of 'our' atmosphere on Earth and that of an 'equilibrium' Earth, as well as the atmospheres of Venus and Mars. Recent 'Earthlight' modelling (simulating viewing the Earth's atmosphere from stellar distances) suggested that the presence of oxygen, carbon dioxide and water would be detectable, as would the presence of oxidising and reducing gases. This latter would be a key indicator of life processes occurring. Life is very adaptable and resilient, as shown by biota having survived 5 Mass Extinction events. Extremophiles reiterate this point. Possible communication with extraterrestrials was then considered: the Drake/Green Bank Equation was very briefly mentioned (see Steve's article) before a hasty skip through Information Theory... Zipf's Law can be used to assess the information content of suspected communications from extraterrestrials (or of suspected languages of terrestrial creatures). This assessment does not relate to the meaning of the communication. On analysis, an increase in complexity of the information content implies increasing amounts of information are being conveyed.. All human languages give a -1 slope when plotted, as do Dolphin whistles... Shannon Entropy looks at communication complexity, giving rise to the possibility of alien languages with, for example, multiple negatives (i.e 'this is not not hasn't not...'), which would make things rather tricky! In sum, Information Theory can give a precise measure of communication complexity. Present and upcoming space missions relating to the search for life were outlined, including the ill-fated 'Beagle 2', and the (hopefully more successful!) 'Huygens' probe - due to parachute onto Saturn's moon Titan this year. Extrasolar planet-detecting missions include Canada's 'MOST' (to detect directly light reflected by giant planets). In 2012-2015 NASA's 'Terrestrial Planet Finder' and the European Space Agency's 'Darwin' telescopes are due for launch. Both will survey nearby stars and analyse planetary atmospheric spectral lines, looking for oxygen, ozone, methane and water. Finally, a brief mention was made of the Strong and Weak Anthropic Principles and Lee Smolin's 'breeding universes'. Dave Ladbrook
Mach’s Principle, Gravitational Waves and Missing Mass - Richard Phillips
Go out on a clear night and look up – the Universe appears to be stationary. Spin round on the spot and the Universe appears to rotate – not only that, but one’s arms rise up from their usual hanging position – perhaps you might surmise that this is due to centrifugal force. Is there a connection? Where does this force come from? Mach reasoned that there is a connection and the appearance of the force is due to the acceleration of the Universe (anything in circular motion is accelerating towards the centre). A person in a box suspended by a chain in a gravitational field will observe that a dropped ball accelerates downwards and deduces that there must be a downward force on it. Newton said that the force F = mass x acceleration. However, if, during the experiment, the chain breaks, the ball will be seen to have stopped accelerating (both the observer and the ball are in free-fall). The question must arise "What happened to the force?". Mach’s answer is that it is cancelled by an equal force upward caused by the acceleration of the Universe upward. In other words, the accelerating Universe ‘induces’ an upward force F’= F on the ball! Far fetched? Trespassing on the realms of Astrology? Not at all. There are similarities between gravity and electricity. The attraction between charges and that between masses both obey an inverse-square law. This causes it to drop off enormously with distance, which undermines any planetary influence claimed by astrologers. On the other hand, the force cause by an accelerating electrical charge drops off with distance only. Maxwell’s equations derive a law of electrical induction in which the force due to an accelerating charge is inversely proportional to the distance from it. Perhaps there is a matching law of ‘gravitational induction’ where an accelerating mass induces a force on a second stationary mass also proportional to the inverse of the distance! In addition, Maxwell’s equations led to the concept of electromagnetic waves – one might surmise that a law of gravitational induction implies the existence of gravitational waves, travelling at the same speed as light does! At this point, the speaker was unwise enough to put a few equations to the audience. In plain English, the equations showed that the fall off of influence with distance is compensated by the amount of accelerating matter at that distance – although at twice the distance the effect of a single piece of matter is halved, there is four times as much matter that is accelerating so the total effect is doubled. Similarly, at three times the distance the effect of a single unit of mass is a third, there is nine times as much matter that is accelerating so the total effect is trebled. The result - the further away the accelerating matter is, the greater effect it has! By adding up these effects to the ‘edge’ of the Universe (where galaxies are receding at the speed of light – gravitational waves from anywhere beyond that distance haven’t arrived and therefore have no effect) the speaker arrived at the following equation for the induced force: F’= mass of the ball x acceleration x 2p x G x (average density of the Universe) (Hubble constant)2 Where G is the Universal constant of gravitation. But, F’= F = mass of the ball x acceleration before the chain broke, so that the big expression on the right should be equal to 1! You all know the value of p, G is well known and we now have a pretty good idea of the Hubble constant. The only thing we don’t know is the average density of the Universe. However, we can calculate it from the above equation. What has been measured by Peebles and Partridge in 1967, is the average density of the visible Universe i.e. the galaxies, and we were able to compare it with the calculated value of the average density of the Universe. Putting the known values into the equation above, we found that: Density of the Universe = 64 x Average density of the visible Universe In other words, we have only detected about 1.6% of the mass of the Universe needed to explain the behaviour of falling bodies on Earth! So, from the original simple experiment we arrived at the current problem of cosmology: – what constitutes the missing mass? Richard Phillips
A Model of the Orbit of Comet C/2001 Q4 (NEAT) Dr. Rodney HillierThis comet was discovered by the orbiting Near Earth Asteroid Telescope back in 2001 and therefore is expected to become quite an impressive spectacle to the unaided eye (though not in the same league as Hale-Bopp), when it swings round the Sun early in May 2004.
The project is sponsor by the William Herschel Society and it is proposed to enable students to report their observations to the Society web-site http://www.williamherschel.org.uk
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