A summary of February’s main meeting

Dr Colin Wilson of Oxford University showed us how modern technology could be both a curse and a blessing when he couldn’t get his planned talk to work, so he quickly accessed the university online and downloaded two Venus talks from his database…and melded them beautifully.
‘The Cloudy Veil of Venus’ dealt with our knowledge of Venus over time, followed by ‘The Case for Venus Exploration’.

Venus is the most Earthlike of the planets and is our nearest neighbour.  Visual images of Venus are bland.  Ultra-violet images are much clearer and show the upper atmosphere rotating every four to five days, while the surface takes 240 of our days to perform a full rotation.  That is a factor of 50:1.  (He compares it to our jet stream, which orbits ten times faster than the Earth’s rotation.)  Earth-based UV studies use wavelengths between 280 and 200nm.  The shorter wavelength gives you more contrast but the planet’s heat and minimal magnetic field makes it difficult to observe.
According to Dr Wilson Pythagoras could see the phase of Venus so was able to conclude that the universe was Sun-centred.
The Venus Express spacecraft is the only craft out there at the moment.  It is Europe-run and arrived in 2006.  It has a highly elliptical orbit, which takes it from 66 to 200km from the surface.
But, the first Venus missions date from 1961 – very early in the space race, but there were lots of failures until Mariner 2 (Nasa, 1962) managed a flyby and detected its incredible heat – a surface temperature of 4500C.  Until then in was thought Venus was a watery world, but of course we now know it has suffered from a runaway greenhouse effect.
Later craft such as the Russian Venera probes and the Magellan radar mapper discovered the surface to be volcanic.  The original Venera images were very orange but when colour corrected to white light the surface is very dark.  (Don’t forget also that only 2% of light gets through to the surface.  Remember the Moscow in a thunderstorm at midday analogy.)
Mariner 10 in 1978 originally detected the polar vortex, which is constantly changing shape and sometimes is three-sided (so not quite as odd as Saturn’s six-sided polar vortex).  You would see it as a hole if you were overhead.
Dr Wilson asks are the volcanoes active.  Thermal infra-red imaging indicates that some are hotter than the surrounding areas, but that they have not been active for a million years. However, some hot patches have recently been detected in the volcanoes, but that information is not yet published so I’d better shut up about that. 

Russia is planning to land another craft on Venus but not until 2022 and it will be getting some help from Japan and the USA.  How things have changed.  A new Venus radar will be able to give a spatial resolution of one to five metres (compared to Magellan’s 100m at best). The surface of Venus is about one billion years old.  It is dated by using the proportions of noble gases detected.

I’d like to add, in case you do read all that, that you can catch the phase of Venus in the morning but that Venus is becoming more gibbous and smaller by the day.  (That should be elsewhere in Spacewatch thanks to Bob.)

Gwyneth Hueter.

Abingdon Clubs and Societies day

The society has a stall at the Abingdon Clubs and Societies day which takes place tomorrow (29/3). This takes place at the Guildhall, Abbey Close, Abingdon, OX14 3HL, from about 10am onwards. It usually ends about 4pm. 

If you’re in Abingdon then do drop in and say hello. If you can spare an hour to help out on the stall that would be great and much appreciated.  


A Summary of January’s main meeting

Bob Marriott (BAA Instruments’ Section) talked about the ‘Silver on glass revolution’.

The 1850s witnessed a massive revolution in science and astronomy.It was long known that reflector telescopes could give good results and that experimentation found that a copper and tin combination (two thirds copper, one third tin) gave reasonably good reflectivity, especially when a little arsenic was added. Unfortunately the arsenic made the surface tarnish very easily, so the hunt was on to see if it was possible to deposit a metal film on glass. (When John Herschel was working in Cape Town in the 1830s he used three 18” mirrors in rotation in his telescope. They had to be repolished and refigured every two to three weeks.)

Both Justus Liebig, an industrial chemist (also of Oxo and Marmite fame), and Michael Faraday experimented with using alkalides to deposit metals on glass. Faraday was only about 18 at that point.
John Stenhouse (who invented the carbon filter which became the basis for the gas mask) did lots of experimental work, adding various oils into the mix.

By the 1850s a silver nitrate preparation with a glucose reducing agent (look it up!) was able to give a good result, but unfortunately the glass itself was still not optically good enough for use in reflectors, even the best Venetian glass.

The 1850s were very busy as regards events: the Hyde Park Great Exhibition (1851), Cholera epidemic (1854), and Crimean war (end 1850s onwards). James Clerk Maxwell was playing with photography and by 1861 had managed to take the first colour photograph. In the meantime Warren de la Rue wrote on the progress of silvering and Webb’s ‘Celestial objects for Common Telescopes’ came out in 1859, the same year as the massive Carrington event (solar eruption).

The art of silvering glass was finally perfected by Leon Foucault in 1857, but speculum metal mirrors continued to be made.

What pervaded Ian’s high-speed talk was the enthusiasm that the Victorian astronomers and scientists had. Many of the names are familiar to us; do look them up: William Lascelles, James Nasmyth, William Huggins, Henry With, George Calver. And they were almost all amateurs.

Gwyneth Hueter.