Alan Bell's talk "Sids, Whispers and Pings" explored some of the effects of astronomical phenomena on radio communication. He began by giving us a short list of the scientists who laid the foundations, and then explained a little about the ways radio signals can travel round the Earth. Long-range radio communication is greatly affected by astronomical phenomena, most of which are caused by the Sun. Sunspots affect the strength of the reflective layers in the Earth's ionosphere, and solar flares can affect them dramatically. The charged particles from solar flares can both help and hinder, and Alan played some recordings of long-range communications made using reflections off an auroral curtain to illustrate the distortions introduced by the particles' spiralling paths. Meteors also produce ionisation trails, and these have been used as reflectors for long-range radio. Conversely, over-the-horizon transmitters can be used to count meteors. The Moon can also be used as a reflector for radio transmissions, but its distance and low albedo make it an extremely tricky intermediary to use. Alan concluded his talk by describing some of the natural forms of interference produced by astronomical sources like the Sun, Jupiter, the Milky Way's core, the Cosmic Microwave Background, and pulsars. He mentioned the Crab Pulsar specifically, because its frequency and occasional outbursts make it a particularly bizarre source of occasional interference for 60Hz TV signals.

In Alan Longstaff's talk "What have meteorites ever done for us?", we heard a great deal about the composition and structure of meteorites, about element and isotope ratios, chondrules, Widmanstatten patterns, and much else. Meteorites are clearly fascinating and worthy of study, but the real surprise is in just how much they can tell us about the very early stages of our Solar System's formation. By carefully lining up the evidence it is possible to make a case, not only that the formation process was initiated by a nearby supernova, but also what type of supernova was most likely responsible. By comparing meteorites with lunar and terrestrial rocks it's possible to date the event that formed the Earth-Moon system. By studying isotope ratios in an ancient Martian meteorite it is possible to challenge the presumption that Mars experienced a long wet period early in its history. Much has been learned by studying meteorites, and there is very likely a great deal more yet to be learned.

At our August meeting at the Scout Hall in Green Street Green, Greg Smye-Rumsby presented us with a fine selection of three-dimensional image. Some were constructed from raw distance data, others used pairs of images, and many were constructed by using the cues in a single image. A few were of star fields, galaxies and nebulae. The majority featured ojects in our own Solar System. While many of the images from various space probes and manned missions have become quite familiar, the extra dimension gives them more impact, and helps bring out features which might otherwise remain almost un-noticed.

After our Chairman Jim Mehta had opened the meeting, Chris Suddell gave us a short talk about some of the less well-publicised aspects of the Cassini-Huygens mission, including an image of the Eta Carinae nebula, an ultra-violet image of Hyperion, and revealing infra-red images of Saturn and Enceladus. Then Tony Sizer gave us a talk about the naming of the constellations, with particular emphasis on the many and various names invented for the ones in the southern hemisphere, the rivalries between some of the astronomers involved, and the eventual finalisation of the constellation boundaries by the International Astronomical Union.

Richard Westwood began his talk about "History of Planetaria" by mentioning briefly various mechanisms and devices used before the 20th Century to illustrate the heavens. He then went on to describe the various planetarium projectors which were produced during the 20th Century, starting with the first Zeiss projector. While Zeiss dominated the market for much of the century, other manufacturers (particularly Spitz, and later Minolta) also had an influence. A few one-off projectors were made too. Perhaps the most notable was the one made for the Morrison Planetarium in San Francisco, which had several star projection domes to better project stars of differing magnitudes. Another interesting development was the Norton Atmospherium, which attempted to show all manner of sky conditions. Digital planetaria are the most recent innovation, with the first being the Evans and Sutherland Digistar. One of the most modern is the new planetarium at Greenwich. It is controlled by a bank of computers and uses red, green and blue lasers to project its stars.

This evening's meeting started with our Chairman Jim Mehta giving us some of the latest astronomical news, Chris Suddell showing us a long-exposure image he'd captured last night from the field at Tuesnoad, and Tony Sizer explaining the complexities of the new planetarium at Greenwich.

The main talk about "Venus Express" was given by Dr. Andrew Coates from UCL and MSSL. He began by describing some obvious differences between our Solar System's four inner planets. Mercury and Earth have magnetic fields strong enough to protect them from the Solar Wind. Venus and Mars do not have significant magnetic fields of their own any more, so they feel the full force of the Solar Wind. Venus also has a very dense super-rotating atmosphere. The planet itself rotates very slowly in the "wrong" direction, but its atmosphere is rotating much faster, so that it has vortices at its poles. Parts of its atmosphere go all the way round the planet in as little as four Earth days.

The Venus Express mission was designed to be able to look in depth at Venus' atmosphere, from its lowest levels to the ionosphere and its interaction with the Solar Wind. Unfortunately one of its seven main instruments is not working, but the remaining six are producing lost of information. The ASPERA instrument is used to determine the charge and composition of the plasma the Venus Express craft is passing through. The elliptical orbit maintains a fixed orientation with respect to the stars, so as Venus goes round the Sun the craft can build up a picture from a full range of orientations. It can directly measure the planet's bow-shock and related phenomena, and detect the quantity and composition of the plasma being stripped from Venus' atmosphere by the Solar Wind. It seems Venus is having much more matter stripped from it than previously expected. Curiously, a similar instrument on Mars Express has determined that Mars is losing less matter than expected. Similar instruments are also in place on Cassini to measure the effects on Titan's atmosphere of Saturn's magnetosphere, and on Rosetta, which will go into orbit around a comet.

Other instruments on Venus Express have taken detailed images of the planet's atmosphere at many levels, and the complex double-vortex at the planet's south pole is particularly fascinating. Future highlights include a fly-by of Messanger on its way to Mercury. Briefly, Venus will be being studied by two spacecraft at the same time. There are also opportunities for amateur astronomers to help the mission by imaging Venus using particular filters at set times. For more information, see the ESA website at sci.esa.int.

Nik treated us to show of some of his best images while giving us context and tips to help improve our own technique. A notable moment was Nik's surprise at the large numbers of members who consider themselves Astrophotographers, suggesting it's more usual to have a couple of photographers, not the twenty plus who admitted to dabbling!

Finally, Nik wrapped up the evening with a question and answer session, and was only let out of the building once our members felt that they'd had as much astrophotography help as Nik was able to supply.