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Wed, 20 Jun 2012 - Transit of Venus, 6 June 2012


The Transit of Venus across the face of our Sun on the 6th of June was, for some, a fascinating event; for others it was something of a wash out. The weather at my observing site in Scotland was firmly in the latter camp consisting of solid cloud and rain; others were luckier. Here are a few of the images that have, so far, been sent in to the planetary section by both members and by outside contributors.


One of the best has come from Peter Grego and his observing companions, Paul Stephens and John Spittle, who were observing from Long Marston. Venus is very much a twin of Earth in terms of physical size yet it pales into insignificance when compared with the size of the Sun; remember the Sun is some 60 million miles further away than Venus! Please note the small projections of light wrapping around the dark body of the planet; this is light from the Sun refracting through the deep planetary atmosphere.




















Jim Lafferty was kind enough to send in this image taken through a solar Hydrogen-Alpha filter and taken from California. Pictures like this really puts the size of our Sun in perspective I feel.












Cristian Fattinnanzi sent in this lovely image of the Sun rising in Porto Recanati, Italy. The scale of Venus is, again, very apparent.


















How the transit should appear shortly after sunrise – a photo adapted from the 2004 transit. Photo by Robin Scagell







A Transit of Venus takes place when Venus crosses in front of the Sun, so we can see the globe of the planet silhouetted against the Sun's disc. A transit took place on 6 June 2012. You might think that this would be a regular occurrence – after all, Venus passes between the Sun and the Earth every so often as it orbits the Sun closer in than Earth. But the two orbits are inclined by a few degrees, so a transit can only take place when both planets are close to the point where the planes of the orbits cross.

This happens only twice every century – or to be more precise, eight years apart, with a gap of up to 121 years between the pairs. The last Transit of Venus was in 2004 and the next transit will not be until 2117.

However, unlike in 2004, when the UK was fortunate enough to see the whole event lasting several hours, and enjoyed clear weather over much of the country, the 2012 event was much more difficult to observe because most of the event took place before the Sun rose. Only the last hour or so was visible – and at sunrise. So by the time most people woke up, it was all over.

Great care is needed when observing the Sun, even when it is low down. Its brightness can easily blind you, particularly when viewed through optical aid. The only safe ways are to use a filter specifically designed for solar observing, or to project the image through binoculars or a telescope onto a white screen. For further information on safe solar observing, see our comprehensive online guide.

Past observations of Transits of Venus involved tales of high adventure and discovery. Tony Sizer, lecturer at the Royal Observatory, Greenwich, presented a talk on the subject at a recent SPA meeting which you can view online. Or to hear the full story, get the DVD of a lecture by the inimitable Dr Allan Chapman, given before the 2004 transit, available from the SPA Shop.


Added by: Robin Scagell