On behalf of the Council, I send you Christmas Greetings.
December 14th: Dr Graham Wallis (Hampstead Scientific Society)
January 18th: Dr Elspeth Garman (University of Oxford)
WHY WE KEEP CATCHING THE 'FLU
February 22nd : Dr Chris Welch (Kingston University)
March 22nd: Dr Pamela Greenwell (University of Westminster)
April 26th: Professor Robert Weale (Hampstead Scientific Society)
BROCCOLI AND EYESIGHT.
Doug Daniels, Astronomical Secretary Hampstead Scientific Society
It comes as something of a sobering thought that I have been demonstrating at our Observatory regularly for a little over 40 years. Thanks to our dedicated band of enthusiasts, the Observatory is opened regularly during the winter months on clear Friday and Saturday evenings and Sunday mornings, to afford members of the public the opportunity to view some of the wonders of the Universe through a decent telescope. It is an equally sobering thought that this service has been provided, almost unbroken, for the best part of a century. During this time, we have observed a steady decline in observing conditions up at Lower Terrace.
I am not just talking about light pollution. When the Society was founded in 1899, the local area up on Hampstead Heath was totally dark and visitors could view the full splendour of the Milky Way. The greater part of London was still lit by gas lighting and vehicles were horse-drawn. Of course even then there was atmospheric pollution, mainly from the burning of high sulphur content coal in domestic grates by a rapidly expanding population and from the equally rapid expansion of industry in the city below. London fogs were a regular feature of autumn and winter months, but the Observatory, situated at the highest point in London, was often above them. Atmospheric pollution continued to increase for decades and in the 1950's one of our Society's members, Leo Bonacina, made a study of the visibility across London. For years, he took sightings from a spot on Parliament Hill, making daily recordings of the visibility of distant horizons according to a scale which he had devised. His observations showed a steady decline in visibility over time.
In the 1960's the Clean Air Act was introduced which banned the burning of coal in domestic grates and imposed strict regulations on industry. For a short time air quality and transparency showed steady improvement. This improvement was, however, to be short lived due to the increased numbers of motor vehicles and the resultant increase in pollution from their exhausts.
Now we are facing a new menace: pollution from aircraft. Over the last few years the number of aircraft movements over London have increased and they are set to go on increasing in the future. From my own observatory in Finchley, I have witnessed an enormous increase in aircraft movements during the last 40 years, currently running at about 250 per day. Aircraft release tonnes of carbon dioxide and water vapour directly into the atmosphere, which can severely affect local atmospheric transparency; they can literally alter local weather conditions. This was clearly demonstrated in the USA when all aircraft were grounded for a short period following the terrorist attack on the World Trade Centre.
Pollution from aircraft is probably the greatest contributor to the effect known as Global Dimming. This phenomenon has been confirmed by examining the records of 'pan evaporation' experiments, in which an open pan of water is allowed to evaporate naturally. The time taken for the water to evaporate is a measure of solar radiation. World-wide records of pan evaporation experiments over time have shown a marked increase in evaporation times, indicating a diminution of solar radiation, caused by atmospheric pollution. It is somewhat ironic, that without this effect, Global Warming might be even more pronounced! Nevertheless, two 'wrongs' do not make a 'right'.
When the Hampstead Observatory was founded, a century ago, visitors could see the Milky Way and stars down to the sixth magnitude with the naked eye. Now we feel lucky if we can see stars of the fourth magnitude. But our records indicate other worries concerning the frequency of clear nights. Three decades ago one could expect that at least one in three weekends would produce a clear night. That is no longer a reasonable expectation. In 2003 I recorded the number of clear nights at weekends. I discovered that from mid September until January there were a possible 48 occasions on which the Observatory could have been open. In the event, 42 nights were totally cloudy. From October 18th until December 28th there was not a single Friday or Saturday evening or Sunday morning that was clear. That is an interval of 10 successive weeks when observations were impossible at weekends. I have noticed this disturbing trend developing over the years.
Why is it now less likely to be clear at weekends? It has been suggested that it is due to the steady build up of pollution caused by industry and vehicles during the week that reaches a maximum on a Friday. It then decreases over the weekend to begin a new cycle again on Monday. I am not entirely convinced by this argument. As we now live in a society that sees almost everything open at weekends, I see traffic congestion just as heavy at weekends as on weekdays; in some areas it is even worse! However, when people go on holidays abroad, more often than not they depart at weekends. Does this not mean that there is increased air traffic at such times?
The Hampstead Observatory also features a meteorological station that now holds a record for continuous daily observations from one site. Our records show conclusively that between 1900-2000 the mean annual temperature at the Observatory has increased by fully one degree C. But whether this is a result of the industrial activities of mankind or natural cyclic phenomena is still open to debate. The only thing of which I am certain is that over the last four decades I have seen a steady increase in both atmospheric pollution and light pollution at the Hampstead Observatory coupled with a decline in the number of nights when it is clear enough for observations to be made. These are worrying trends for the future of urban observatories like ours.
The interesting article in the August Newsletter told us that mankind lags behind some other species who can make use of ultra-violet radiation, whereas we cannot. The tentative explanation was Tim Goldsmith's speculation that vertebrate species have evolved with four types of cone, but that the development of rods, useful at night, led in our ancestors to the loss of two types of cone. Of the two types of cone left, one mediates shortish (blue) wavelengths, and the other the longer (yellow-green) ones. The need to distinguish red fruit from green foliage led to a useful mutation in that the cone responding to longer wavelengths evolved to form one responding to a somewhat shorter (green) wavelength. This left two types of cone mediating information on food.
The question arises why, if other species apparently needed for survival cones responding to the ultra-violet part of the spectrum, we had to do without them - and managed to survive. In this connection it is useful to remind ourselves that evolutionary biology operates on Thatcherite principles of economics: it does only what it has to do and, when necessary, sacrifices an existing advantage if the mutation offers a better chance of survival. In our case, our eyes found themselves in a body capable of living much longer than the species considered by Goldsmith. With long life, there also goes a long exposure to sunlight. Added to which, we appear to have originated in Africa, which may have been cooler during our sojourn there but certainly exhibited no shortage of light.
There is an unresolved debate going on whether light affects our eyes in ways other than those mediating vision. For example, as we age, the lenses in our eyes become yellower, transmitting less and less blue and violet light for the retina to see. Parts of the yellowing substances have been attributed to photic effects. Also populations exposed to sunny environments tend to have yellower, or darker, lenses than those less exposed to the sun. On the other hand, direct measurements of ultra-violet exposures did not seem to correlate with lens colour.
However, strong radiation appears to exert an adverse, if not damaging, effect on the retina at the back of the eye. This has been dubbed the Blue-light Hazard because blue light seems to be very effective. Detailed studies on rhesus monkeys and other mammals have shown, however, that the peak of the hazard occurs not in the blue part of the spectrum, but in the ultra-violet part or UVB, with a peak at ~ 335nm. At the moment there is no reason to assume that this does not also apply to our eyes. Now it can be shown that we have evolved a very effective defence mechanism against the noxious radiation, and that is to be found in the yellowing of the lens. The risk to the eyes appears to be highest in youth and declines after the age of ~ 20 years partly because of the reduction in the size of the pupil, which controls the entry of light into the eyes, but mainly because of the progressive coloration of the lens.
It would clearly be poor biological economics to maintain a photoreceptor sensitive to ultra-violet light while evolution has endowed us with a mechanism that absorbs that light, thereby preventing it from reaching a set of retinal cones sensitive to ultra-violet light. Note that the mechanism of lenticular yellowing gets into its stride in our twenties, at an age when our ancestors had to be possessed by good eyesight if the next generation was to be enabled to survive a hostile environment. Tim Goldsmith's birds can probably afford to maintain cones for the ultra-violet because they are unlikely to live long enough to regret it.
In 1966 May Ammon, the Principal of the Ackland-Burghley School approached Doug Daniels to start an astronomy adult evening class at the school. After a year, due to the pressure of work, Doug handed the class over to Terry Pearce, a long-term friend and a keen amateur telescope maker.
During the subsequent years, by popular demand of the students, the class evolved into not just an astronomy class, but a telescope making class, where members were encouraged to grind, polish and figure their own telescope mirrors and build their own instruments from scratch.
By introducing many people to the study of astronomy and telescope making, the class also became a natural source for demonstrators and assistants at the Hampstead Observatory, many of the alumni became members of the Hampstead Scientific Society.
The class continued to meet weekly throughout the intervening years, surviving the closure of the original Ackland-Burghley venue and finally moving to the Westminster Kingsway College. It was at this institution that it was finally closed down two years ago due to 'economic cutbacks'.
The remaining members were not happy with this decision and so the Camden Amateur Telescope Society (C.A.T.S.) was formed to carry on the good work and application was made to affiliate it to the Astronomy Section of the H.S.S.
C.A.T.S. now meets fortnightly at the Highgate Newtown Community Centre and it was at that location that past and present members gathered on the evening of October the 11th to honour their mentor Terry Pearce, for 38 years continuous service to the study of astronomy and telescope making.
At the ceremony, Terry was made Honorary Life President of C.A.T.S. and was presented with a certificate and a trophy, in the form of a model telescope, designed and made by Simon Lang.
The recent summer visit by the HSS to the Culham laboratory was a success. Sited there is the Joint European Torus (JET), involving nuclear scientists from all over the continent, and the UK's own fusion research programme MAST. But only two weeks ago there has been a formal international agreement to construct at a cost of some £7 billion the next stage in the development of power from nuclear fusion, the process that powers the sun. This is called ITER, an acronym for International Thermonuclear Experimental Reactor, but also latin for 'the way'.half the cost will be borne by the EU, with the rest shared by the US, China, India, Japan, Russia and S. Korea. It will be built in Cadarache in France and work will start there in 2008.
Nuclear fusion involves the fusion of hydrogen atoms to form helium, with the release of energy in high velocity neutrons (14 MeV). In the center of the sun it occurs at temperatures of 10 million °C , but we cannot achieve comparable pressures on earth and need at least 100 million °C . The reaction occurs in a plasma of positively-charged nuclei and negatively-charged electrons, contained by magnetic fields to keep it away from the walls.
The raw material for the reactor is water,but we actually fuse two of its heavier isotopes, deuterium and tritium. One litre of water contains 35 mg of deuterium; its fusion with tritium releases as much energy as 340 litres of gasoline. The tritium is manufactured in the reactor by the reaction between the neutrons, which are not constrained by the magnetic fields, and a blanket of lithium to form tritium and helium-3, an inert and harmless gas. The heat in the lithium blanket is removed by a 'coolant' and heat exchangers to steam turbines which generate electricity. There is no chain reaction, so no risk of explosion.
The waste from a fusion plant of 1000 MW power is only 250 kg of helium per year, which is not a green-house gas. Comparable wastes from other power plants of the same power are:
The Geminid Meteor Shower is to be seen in the night of 13/14 Dec, low in the east in the early evening and high in the south after midnight. 60 or more per hour are likely.
Mercury, Mars and Jupiter are close together in a 1° circle in the dawn sky around the 10th December.
Last updated 28-Jan-2018 contact