MedicineLakex

 

Microsoft word - jul11magpdf

The Newsletter of the Astronomy Section of La Société Guernesiaise July – September 2011 Forthcoming
Letter from the Secretary. Perseids BBQ
Energy from Nuclear Observatory: 12th August: Public Open Evenings
Abstracts from Astronomy 28th July: 9.00 pm Obituary: Les Curtis 4th August: 9.00 pm 11th August: 8.30 pm 18th August: 8.30 pm 25th August: 8.30 pm 1st September: 8.30 pm New format will be that Public Open Evenings will be on a Thursday evening and will comprise a talk or film show, with a clear night for observation being a bonus! Sunset, sunrise, moonset and In addition, the Section meets at the Observatory every Tuesday evening, and Friday if clear for observing. Letter from the Secretary.
Debby Quertier has been our Secretary Our first Open Evening this year was for the past 13 years. We have seen on Thursday May 26th when we tried many changes during her time of something different. It was cloudy office, ranging from the purchase of and we could not use the telescopes new telescopes to the complete but we showed them to our Guests and renovation of our meeting room. then had an evening of talks, slide Debby's knowledge of the night sky is shows and general discussion. It went legendary and she easily held the very well and the same format will be interest of everyone during our open used for future Open Evenings (on evenings. We all agree that Debby selected Thursdays) with clear skies a has done a wonderful job and all with a minimum of fuss. We plan to have occasional talks at the So with that background, I have taken Observatory this year, one of us over as Secretary knowing that I have speaking followed by questions and a very difficult act to follow. (hopefully) answers. If anyone would like to know in advance of these We have over fifty members in our evenings, (always on a Tuesday), group who pay subscriptions every perhaps you could give me your e- year and receive the Sagittarius mail or telephone number. newsletter. A healthy 10-12 people regularly meet on a Tuesday evening Finally, I am always open to but there is always room for more. I suggestions for improving the running am in favour of everyone getting from of the Section for its members, or just the Section exactly what they wish, to talk about any aspect of our interest but my only concern is that many do in Astronomy. I do not want anyone not come along because they do not to feel left out. know what to expect. We meet every Tuesday from 8 pm onwards and we Frank Dowding
would be very happy to meet you, talk to you and have you join us for a cup of coffee or tea. So why not give me a Energy from Nuclear Fusion

‘The Sun shines and warms and lights
us and we have no curiosity to know exceptions, when a sense of curiosity why this is so.' While this about the Sun, and indeed about many observation by Ralph Waldo Emerson other wonders in the world about us, is probably true in general, it is has led enquiring minds to make of the electron that the atom, scientific progress. One question that the curious might ask about the Sun is, ‘How does it get matter, did in fact have an inner its energy?' There were two early structure. An investigation of that suggestions put forward to account for inner structure was pursued by the Sun's energy source. Perhaps Rutherford and his research group at radioactive processes supplied the Manchester, in a series of experiments energy, as they apparently did in heating the core of the Earth? It was discovery of the atomic nucleus. A known, however, that the Sun, which further discovery of great significance was believed to have condensed from was also made by Rutherford and his a cloud of gas consisting mainly of group and was published in 1919, by which time Rutherford had moved to insufficient amounts of the heavy Cambridge. That discovery was the first observation in a laboratory radioactive processes. The other experiment of a nuclear reaction, suggestion, made by Lord Kelvin in when nuclei of nitrogen, bombarded about 1860, was that the steady with alpha-particles from a radioactive contraction under its own gravity of source, produced nuclei of oxygen. the mass of material that formed the (For centuries the ‘philosopher's essentially translating gravitational transform one element into another – energy into the energy of radiation. It preferably a base metal into gold – had been sought: it turned out in this case estimated mass and radius of the Sun, to be the alpha-particle.) With that that enough energy could have been discovery nuclear physics could be generated in this way to sustain it at its said to have been born; it later proved present luminosity for about 20 million years. Unfortunately, it was known from geological studies that the generating processes might occur in Earth, and the Solar System including the Sun and other stars. the Sun itself, must be greater than a billion years old. The situation at the In 1920, Eddington suggested that beginning of the twentieth century was energy might be produced in the synthesis of helium from hydrogen, explanation had to be found. with four nuclei of hydrogen somehow reacting to form one of helium. During the early years of the new Following the invention by Aston of century, before the First World War, the mass spectrograph, by means of unknown realm of physics were made. measured with great accuracy, it could In 1897, the Cambridge physicist J J be shown that in this process of Thomson had shown by his discovery hydrogen there would be a minute loss noting here that, in accordance with of mass (about 0.8% of the total), the that calculation, the Sun should be so-called ‘mass defect' ∆m, with the
losing 4 billion kilograms of its mass result that the equivalent amount of per second; but that at its estimated energy, as given by Einstein's formula present age of 5 billion years, it would (∆m)c2, would be released. Eddington
still have lost only 0.03% of its mass calculated from the mass of the Sun hydrogen, the proposed nuclear ‘fuel', In order to make further progress to sustain its energy output by this here, a number of terms used in means for about 15 billion years, that nuclear physics have to be introduced: is for appreciably longer than its these are set out in the ‘box' below. estimated lifetime. (It might be worth Some basic terms in nuclear physics

The atomic nucleus, which has diameter only about ten millionths that of the atom,
accounts (e.g. in the case of hydrogen) for about 99.9% of the total atomic mass.
This tiny, massive nucleus is made up of elementary particles, the proton and the
neutron.
The proton has positive electric charge and the number of protons in the nucleus,
the atomic number, is equal to the number of (negatively charged) electrons in the
outer structure of the atom, so that the whole atom is electrically neutral. The
atomic number defines the identity of the atom, whether it is an atom of hydrogen,
helium, carbon, oxygen etc.; it also determines the place of the element in the
Periodic Table. The same number of electrons, as well as their arrangement in the
atom, determines the chemical properties of that element, that is how it combines
with other atoms to form molecules and chemical compounds.
Within the nucleus itself, different numbers of neutrons, which do not have electric
charge, can be accommodated, giving different isotopes of the same element. The
nucleus of the hydrogen atom is a single proton, but the addition of a neutron gives
a deuteron (D), and the addition of two neutrons gives a triton (T). The
corresponding atoms are deuterium and tritium, respectively. In the case of
helium, with two protons in the nucleus, the isotopes helium-3 (with one neutron)
and helium-4 (with two neutrons) play important roles in the solar nuclear fusion
processes. In any nuclear reaction the particular isotope involved can be critical,
because isotopes of the same element can have very different nuclear properties.
Materials often exist in regions of high temperature and pressure, where the
atomic structure has been broken down to form a plasma, an electrically neutral
state of matter composed of nuclei and electrons, which behaves almost as a gas of
free particles.
Following the work of Eddington, a as being in the ‘Main Sequence' class, further advance was made in 1927 by derive their energy. A most perceptive comment has been realised that at the high temperature made, which is that it is the very slow (about 10 million degrees Celsius) and rate at which the suggested initial high pressure (about 100 billion times phase of ‘hydrogen burning' occurs atmospheric) believed to exist in the that has enabled the Sun to produce interior of the Sun, the hydrogen energy over a sufficiently long time to would form a plasma within which the allow the Earth to form, to cool and to mutual interaction of high energy act as host to the evolution of life to protons (the nuclei of the plasma the level that we know. ‘thermonuclear' For several decades during the late place. As considered by Bethe and by twentieth century it was an ambition, von Weizsacker independently in at that time seemingly impossible to 1938 and 1939, the nucleosynthesis of achieve, to build a device in which helium from hydrogen could then nuclear fusion could be induced to proceed in several stages: first, a take place and, as in the Sun, provide deuteron could be produced from two a source of energy. It was clear at the interacting protons; and then the outset that any attempt to reproduce deuteron could interact with another proton to give helium-3, which believed to occur in the Sun would not undergoes a further reaction to give be successful: the first stage, of helium-4, the final product. The rate deuteron formation, with its billion- of deuteron formation in the initial year timescale, might be possible in stage would be very slow indeed, the Sun, with its long lifetime, but not however, with the probability of any on Earth where, to be profitable, given proton interacting in this way reactions that occur much faster would corresponding to just one interaction have to be employed. event in 14 billion years. The process proposed was nevertheless regarded as Perhaps it might be possible to omit viable, because of the large number of altogether the deuteron-production protons in the solar interior, and process, and instead start with pure because of the long time over which deuterium as the ‘fuel'? Deuterium the plasma could be sustained at the occurs as a component of ordinary water, of which there is an abundance pressure. As a result of this and other in the Earth's rivers and oceans. In a more recent research, it has been high-temperature generally accepted that the nucleosyn deuterium, thermonuclear reactions thesis of helium from hydrogen is the between deuterons, the so-called ‘D- process by which the Sun, and also D' reactions, should occur if the other stars described by astronomers temperature were sufficiently high, more than 100 million degrees

Celsius. An alternative fuel could be a reactions could take place. Different mixture of deuterium and tritium shapes of ‘magnetic bottle' were where, as could be seen from the basic devised, in a variety of experiments. nuclear data relating to the deuteron Eventually, the preferred type of and triton, ‘D-T' reactions (as shown plasma container that emerged was the in the illustration here) should be even hollow, doughnut-shaped vessel, or more productive of energy. Tritium ‘torus', sometimes referred to by the does not occur naturally, but can be Russian term ‘tokamak'. irradiation of the fusion device is Consideration of reached when the in the plasma by fusion, during the the hot plasma can the generation of energy from some be contained, is equal to the energy suitable nuclear fusion process, and to required to produce the plasma in the the dream of obtaining an apparently first place. There is a mathematical unlimited supply of energy from formula that can be derived, which readily available raw materials. The main practical difficulty then lay with parameters of temperature, density and the engineering, that is with the actual design and construction of a device expresses this criterion precisely. The that would translate the dream into aim of any fusion device is to attain critical values of all three of these parameters, if possible simultaneously. Plasmas of high temperature and density are difficult to contain, with The most successful thermonuclear the further problem that contact of a fusion device to have been built so far hot plasma with the walls of its is JET (Joint European Torus) which containing vessel lead immediately to is situated at Culham, near Abingdon its cooling. The idea of magnetic in Oxfordshire, and which has been in confinement, which might be possible operation since 1983. JET was for a plasma of electrically charged deuterium plasma heated by several therefore seemed to be an alternative: million amperes of current, from the it should be possible for a carefully contoured magnetic field to confine temperature of 50 million degrees such a plasma to a space where, in Celsius. One remarkable achievement suitable conditions, thermonuclear of JET has been to attain an ultimate

plasma temperature of 300 million extracted for industrial or commercial degrees, which is about twenty times use. In 2006, the decision was taken the estimated temperature at the centre to build an experimental reactor called of the Sun; but the required values of ITER (International Thermonuclear the three plasma parameters could not Experimental Reactor). The ITER be achieved all at once in the same project is the result of an ambitious experiment. In 1991, with tritium scientific collaboration between a injected into the deuterium plasma, number of technologically advanced JET was able to produce 1.7 nations, and its construction at megawatts of fusion power for about Cadarache, near Marseilles, is due to two seconds and, to quote an official be completed within the next ten report published subsequently, ‘This was the first time that a significant amount of fusion power had been One objective of ITER, as it has been generated in a magnetic confinement at JET since about 1995, is to study the ‘self-heating' of the contained plasma by energetic nuclei created as JET is essentially an experimental by-products of the fusion process. At ITER an additional feature will be a production of plasmas suitable for a ‘blanket', a solid wall shaped around nuclear fusion reactor; it is not itself a the plasma-containment vessel and reactor from which energy could be designed to degrade neutrons also

produced in the fusion process: the which sustains life on Earth. It would neutrons heat the blanket, from which indeed be a great achievement if energy could in principle be extracted. similar fusion processes could, by In any future full-scale reactor (as means of modern technology, be shown in the illustration above), employed to generate energy, using energy would be extracted by means fuel that is both abundant and easily of a ‘heat-exchanger', producing accessible. The basic physics of steam to drive a turbine for electricity nuclear fusion is well understood, but generation, as in a conventionally it requires engineering genius to fuelled power station. The ITER translate this dream into reality. neutrons also interact with lithium incorporated into the material of the In recent decades, the construction of blanket, to produce tritium which, if thermonuclear devices has made ‘distilled out', contributes towards substantial progress in that direction; replenishing the supply of reactor fuel. this had led to a great sense of optimism that nuclear fusion should be ITER should have the capacity to able to provide industrial levels of produce 500 megawatts of fusion sustainable power, not just yet power which, with an input of 50 foreseeable future. impressive power ‘gain'. There is little doubt that nuclear fusion David Falla
processes in the interior of the Sun provide the heat and light energy A Close Moon
km. Dubbed a "supermoon" it Basically it orbits the Earth in an appeared larger than usual, and ellipse, of which the Earth is at one presented a good photo opportunity as focus. The Moon's average distance it rose above the eastern horizon. from the Earth is 384,400 km, but it normally varies from 363,296 km I took photographs with a tripod- (perigee) to 405,504 km (apogee). mounted camera with a 1000 mm focal length lens, and one is shown on However, the eccentricity of its orbit the right in the accompanying picture. changes depending on its relationship with the Sun. When the long axis of photograph the rising Moon on 30 the ellipse lines up with the Sun, August 2007, and this appears as the which it does every 206 days, the left image. The difference between ellipse is stretched by the Sun's the two horizontal diameters is some gravitational pull, and its eccentricity 10%. The horizontal diameters were increases. This results in a lunar perigee less than average, and an apogee greater than average. So its diameters, especially when the Moon distance can be anything from 356,371 is near the horizon. km to 406,720 km, a variation of over David Le Conte
Every 18 years the shortest lunar For further information see Mathematical perigee coincides with the Full Moon. Astronomy Morsels by Jean Meeus (Willman-Bell Inc., 1997), chapters 2 and 3. This happened on 19 March 2011, when its distance was just 356,577

Geoff Falla's regular roundup
massive stars. (Astronomy Now, of articles from popular
Astronomy and Space
Identifying Earth-like Exoplanet
Journals
atmospheres. There is now strong
evidence that terrestrial-type planets Star Clusters. A set of three articles
are more common in our galaxy than focusing on the different kinds of star gas giants. Red dwarf stars are found clusters; the open clusters - often large to be more common than Sun-like groups of the more newly-formed stars; a habitable zone around these stars, having condensed out of a gas stars will be relatively close - so there cloud; the globular star clusters is a much better chance of observing surrounding our Milky Way galaxy, planetary transits, and analysing the but also seen forming in collisions between other galaxies, and super-size (Astronomy, April 2011) clusters containing many of the most Iceland's
Dramatic
and Telescope, May 2011) Displays. Iceland is best known for
its volcanism and the night sky's The First Stars and Quasars. The
"northern lights". Situated in the most universe is now becoming understood active part of the Earth's northern more clearly, that after the big bang auroral ring, Iceland has some of the best auroral displays to be seen anywhere, with the displays visible on there was a dark period before further most nights of the year. (Astronomy, ionization was involved in forming the first stars and black holes, and leading to the modern universe. (Sky and Telescope, May 2011) Anniversary. Marking the 50th
anniversary of Yuri Gagarin's epic New Insight on the Sun. After a year
space flight on April 12th 1961, when in orbit around the Sun, studying it in he achieved the first manned orbital flight around the Earth, and a few Observatory has given astronomers months later made visits to London the ability to understand how the Sun's and Manchester. (Sky at Night, April magnetic field drives solar activity. Three instruments are being used to obtain information from below the The Hunt for Galaxy X. Ripple
Sun's surface and out to the very hot disturbances of hydrogen gas density in the outer disc of our Milky Way has (Astronomy, May 2011) shown that this must have been caused by a dwarf galaxy passing through the When the next Asteroid strikes.
system at some time in the past. The Plans which are now in operation with search is now on to identify this dwarf the Spaceguard Survey, started in galaxy, which it is estimated would be 1998, to identify most of the the third largest satellite galaxy after substantial asteroids in near-Earth the Large and Small Magellanic orbits which may be a future danger to Clouds. (Sky at Night, April 2011) the planet. Asteroids of less than 100 Spinning Hearts of Darkness. It has
widespread damage, but anything been found that most galaxies have larger than a kilometre would need a supermassive black holes at their spacecraft mission to remove it, or cores, with the spin rate of a black divert it onto a different path. hole being a key factor in the release (Astronomy, May 2011) of energy. A black hole also determines how large a galaxy The Ten Greatest Astronomical
atmosphere blocks the high energy X- astronomical discoveries of all time; ray emissions, most of the survey some dating back several centuries, work is from orbiting telescopes. (Sky such as our Sun-centred model of the solar system, and gravitational theory, apparently controls the movement of with others of much more recent planets, other major processes in our origin: the discovery of the cosmic own galaxy, and in all of the galaxies microwave background supporting the beyond. Gravitational lensing, the big bang start of the universe, and the bending of light by massive objects, is current breakthrough in discovering useful in studying some of the most that many of the stars around us also distant galaxies, and there is now a have planets in orbit. (Sky at Night, search to identify gravitational waves which it is thought must exist. (Astronomy Now, June 2011) Variable
luminosity of many stars - some In Search of the First Stars. The
Hubble Space Telescope has been able ranging from days to years in some to obtain images of stars and galaxies cases, while the brightness of other much farther away in space and back stars can vary because of eclipsing in time than previous telescopes could companion stars or more dramatic achieve. Now with images coming reasons. (Astronomy Now, May 2011) from an estimated 95 per cent of that distance back to the original 'big A Search for Vulcanoids. It was
bang', it is expected that the new once thought, from occasional claims, James Webb Space Telescope now that there could be another small being built will halve the remaining planet between Mercury and the Sun. gap back to the start of the universe. The existence of such a planet - which (Astronomy, June 2011) was given the name Vulcan, has never been confirmed, but it is now thought BAA meeting in Jersey
likely that small asteroids may be located in that region, and a search has The 2011 Autumn Weekend Meeting been started to find them. (Astronomy Association is being held at the Radisson Blu Waterfront Hotel, St. Mercury Orbit mission - First
Helier, Jersey, from 2 to 4 September, Image. The Messenger spacecraft has
with the majority of talks being on the obtained the first image of a Saturday. It promises to be an previously unseen part of Mercury, showing a crate red surface, including a prominent rayed crater named Saturday lunch) and David Le Conte Debussy (rather like the ray system around the lunar crater Tycho) and a small crater with unusual dark rays. Details and a booking form are (Astronomy and Space, June 2011) enclosed with this newsletter. They are also available on the BAA website The Invisible Force of Gravity.
at http://britastro.org/baa/. Although a weak force, gravity Obituary:
Les Curtis (1947-2011)
I was shocked to hear of the sudden death of Astronomy Section member Astronomy Section Officers
Les Curtis on 26 March, at the age of just 63. Les was a well-respected dentist, but he was also a man of many interests. I knew him primarily through La Société Guernesiaise, where he was a keen student of marine Public Relations biology. He served on the Société Council. He was not an active member of the Astronomy Section, but he clearly had a peripheral interest in the Observatory
subject; we did see him at the Rue du Lorier, St Peters, Observatory occasionally and he often attended lectures. He was also a keen singer - we sat next to each other in the basses of the 2010 Liberation Day Guernsey Sings performance. www.astronomy.org.gg His death was totally unexpected. He had been attending a marine biology Material for, and enquiries about course in England when he suffered a Sagittarius should be sent to the Editor massive heart attack in his hotel room. I shall miss the friendly smile which he always had, and his readiness for a 60 Mount Durand, St Peter Port chat. I represented the Section at his Guernsey GY1 1DX Tel: 01481 721997 funeral in a packed St Andrew's [email protected] Church, at which the Bailiff read a lesson. Les is survived by his wife, Articles in Sagittarius are copyright the authors. Views expressed are those of the authors and are not necessarily endorsed by the Astronomy Section or La Société Guernesiaise. David Le Conte
Copy deadline for next issue is
30th September 2011
La Société Guernesiaise, Candie Gardens, St Peter Port, Guernsey GY1 1UG.

Source: http://www.astronomy.org.gg/newsletters/Sagittarius-2011c.pdf