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

Newsletter April 2014

Dear member,

Once again the 'end of term' approaches to conclude yet another successful year for our Society. Membership has declined slightly but still remains at 111 members – sufficient to cause problems if they all turned up to a lecture evening! Meetings throughout the year have been well attended and as usual our Programme Secretary produced an interesting and varied programme of talks. We have been particularly pleased to see younger members attending.

Last year the Society had unprecedented good fortune with an anonymous donation of £15,000 to the Observatory maintenance fund. Then shortly afterwards we were fortunate to receive a bequest from the late John Hayden's estate amounting to almost £12,000. These sums put the Society in a sound financial position, a condition never before achieved in its long history. This means that we can continue to keep our subscription at a low rate and we have already obtained a 'state of the art' Hydrogen Alpha Solar telescope and a robotic mounting to add to the equipment at the Observatory.

We have just two more lecture meetings in the current session. The next lecture of the session takes place on Thursday April 17th at which Dr. Akram Alomainy from Queen Mary, University of London, asks the question CAN YOU MAKE YOURSELF INVISIBLE? – I just hope we can find him in good time. The final lecture of the session is on May 15th when Prof. Steve Swithenby . Open University, talks on: THE WORKING BRAIN.

The final meeting of the session is the ANNUAL GENERAL MEETING which will take place on Thursday June 26th with the usual wine & cheese and a scientific entertainment, for which there is a small charge of £3.

The agenda will include reports from officers and section leaders and the election of officers and 5 ordinary members of Council. Council proposes the following:

Secretary
Treasurer & Membership Secretary
Programme Secretary
Ordinary Members (Max 5)
Dr. Julie Atkinson
John Tennant
Jim Brightwell
Dr. Kevin Devine, Roger O'Brien, Martin Williams, David Brandt

At present three ordinary members have served for four years. Under the revised Constitution (revised last year), Council will replace one ordinary member, from those who have served longest, each year. At the Council meeting on April 10th by secret ballot, it was decided that Peter Stern should stand down on this occasion. We thank Peter for his support during the last four years and hope that he will return to Council in the future. This leaves a vacancy for one ordinary member of Council. Council invites further nominations for the above posts. Such nominees should be duly proposed and seconded and should have agreed to serve if elected.

Observing the Sun in a 'New Light'

Doug Daniels

Most of the objects that we direct our telescopes towards are comparatively faint, but the one exception is the Sun. The Sun is such a powerful emitter of light and heat, that observing it telescopically is fraught with danger. On a nice sunny day, a simple hand lens, focusing the Sun's rays on a piece of paper will soon have it smouldering and catching fire. Needless to say: Pointing any optical device at the Sun, such as a telescope or binoculars will magnify the light and heat to very dangerous levels indeed and if you are daft enough to put an eye to it, permanent damage to eyesight will be your reward. It is not even a good idea to look directly at the Sun with the naked eye. This intensity of solar radiation makes observing the Sun a difficult and dangerous business requiring special equipment.

Many years ago at the Observatory, we had a special diagonal eyepiece called a Herschel wedge. This consisted of a shallow angle unsilvered prism which reflected 10% of the light from the prism surface and allowed the remaining 90% to pass 'safely' out of the back. I remember one visitor using this device totally unaware that while he was enjoying a good view of a large sunspot group, the 90% excess light and heat was busily burning a hole in his tie! We no longer use Herschel wedges and today, ties are no longer de rigueur for solar observers.

The safest way to observe the Sun is by projection. Because the Sun is so bright, we can focus a projected image of it on to a white screen behind the telescope eyepiece. This will show the coarser features such as sunspots and faculae and it has the advantage that the view is available to several observers at the same time. We could also use multi-layered coated filters mounted in front of the objective lens. These filters can reduce the brightness of the Sun down to brightness of the full Moon. Such filters will allow us to see much finer detail such as the granular appearance of the Sun's photosphere. But the Sun has much more subtle detail to reveal such as the solar prominences – the flame-like features writhing up around the limb, the dark filaments, sunspots, flares, and the bright swirling 'plages'. These features are normally masked by the Sun's full spectrum white light radiation and to see them we need some very special equipment.

Hitherto, the only opportunity to view prominences was during a total solar eclipse or with a coronagraph located on a mountain top or with a specially designed spectroscope to view the image in the wavelength of hydrogen. Many years ago we actually had such a spectroscope, built by F.J Sellers, the renowned solar observer, but there were few observers with the patience to use it. One had to align the Sun's limb exactly on the Hydrogen alpha line in the spectrum, if you could find it, then slowly open the slit. If there was a prominence in that location you could just about see it before the inaccuracies in the telescope drive moved the slit off the H alpha line and the prominence promptly disappeared. Despite the difficulties using this instrument, the late Henry Wildey used it to great effect and made numerous observations and drawings of solar prominences in the 1950's. Sadly, the Sellers spectroscope was stolen from the Observatory over two decades ago and since then we have had to content ourselves with observing the Sun by projection.

But luckily for us, technology has moved on and we are now able to observe in complete safety, all those subtle aspects of the Sun formerly hidden from us with our recently acquired Coronado Solar Max telescope. This remarkable instrument employs narrow pass-band filters – etalons that allow us to view the full disk of the Sun in the H alpha wavelength. The prominences can be viewed all around the Sun's limb, slowly changing shape over time. We can observe the bright swirling plages, the fine detail around the sunspots, the full granular appearance of the photosphere and the dark filaments and flares which are all easily seen. This adds a new dimension to our solar observations and shows the Sun in a totally different light. If you haven't already done so, come and see what our closest star really looks like when viewed in the wavelength of its main constituent – Hydrogen. The Observatory is open for solar observation from 11.00 am-01.00 pm on clear Sunday mornings until May 18th. Well worth a visit.

Whither Batteries?

Peter R Wallis

The enormous development of mobile miniaturised electronic devices over the last three decades has depended upon the parallel development of small rechargeable batteries. The winner today is the lithium-ion battery. They now offer an energy density of 250 Watt hours per kilogram (Wh/kg), five times the performance of lead acid and the nickel-cadmium of old AA batteries and twice that of the newer nickel-metal hydride in new AA batteries. The Li-ion battery has two electrodes, one of layered graphite, the other a layered metal oxide, separated by a liquid electrolyte through which the lithium ions flow. It is generally thought that they are near their limit, with only a 30% extra performance to be gained. So much thought is being aimed at where to go next. Li-ion is pretty fine for your mobile, camera and laptop, but as a power source for a motor car it will only achieve half the range of an IC engine and fuel tank, is more expensive and takes longer to recharge.

One chemical engineer Elton Cairns at Lawrence Berkeley National Laboratory is working on a lithium sulphur system which he says can save weight and might achieve 500 Wh/kg. Oxis Energy of Abingdon have run large cells of Li-S for 900 cycles and hope, with Lotus Engineering to reach 400 Wh/kg by 2016 for an electric vehicle.

Lithium is the lightest metal but its ion only carries a single charge. The use of magnesium has therefore been proposed as it carries two electric charges; however there are many uncertainties about what electrolyte to use.

Another line of study is air-breathing batteries for cars. These do not have to carry around one of their main ingredients. A Li-O battery could, in theory, store energy as densely as a petrol engine, more than ten times better than current battery packs. Na-O would be a much cheaper alternative, though it would have only half the energy density of Li-O, but that is still five times better than Li-ion. A team including Juergen Janek and Philipp Adelhelm at Justus-Liebig University of Giessen in Germany found that a Na-O battery recharges more efficiently than Li-O without complicating side reactions. Chemical giant BASF is now working with them.

There is another important area in which we are going to need energy storage: Electric Power. Too many of our future power sources will offer only intermittent power: wind turbines when there is no wind, solar power at night or in bad weather. Sometimes they offer more than we immediately need and it would be good to store it for later use. If batteries are to play a part, smallness and lightness will be unimportant; cost and low maintenance will be what matters. The field is wide open with many technical options. Flow batteries are an interesting idea, in which the fuel consists of two liquids which pass ions to each other through a membrane. The liquids can be held in separate tanks and pumped to flow past each other when power is needed. It is possible to store much larger power by using bigger tanks. Currently the world's largest flow battery is installed at a wind farm in China, but it uses vanadium, very expensive! Watch this space.

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And finally Physics teacher to students: "No, It's not an optical illusion, it just looks like one!"

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Last updated   27-Jan-2018