Transit of Venus

Exactly 1yr, 1month & 1day after Mercury, on the morning of Tuesday 8th June 2004 the planet Venus (pictured left) took its turn to be in transit (or passage) across the face of the Sun. Because Venus goes round the Sun much more slowly than Mercury, transits of Venus are among the rarest of planetary alignments: only six such events have occurred since the invention of the telescope (1631, 1639, 1761, 1769, 1874 & 1882) and no living person has seen one. Transits occur in pairs separated by 8yrs, with pairs recurring at intervals of 121.5 and 105.5yrs, so if you missed this one at least you've only got to wait another 8yrs! You'll have to travel though, as its full duration is not visible in England.

The transit was due to start at about 6:20BST in England, be of maximum extent at around 9:20 and end by 12:25. Experience with the Mercury transit had indicated that the only convenient viewing position for my refractor telescope suffered from obscuration by trees, but due to the higher position of the sun in the sky this would clear at about 8:30am. Conversely, due to the longer duration of this transit, the house roof would come into play before the end! This would still give an adequate viewing period though so I decided to persist with the projection method but this time used a translucent screen supported on music stands (necessity being the mother of invention!) in an attempt to avoid many of the distortions experienced when photographing the Mercury transit.

Since the previous transit I had been experimenting with astro-photography using a digital web-cam through my recently-acquired 114mm reflector, so I was intending to use this instrument as well as the refractor. The web-cam connects to a laptop computer which has to be in shade to see anything on the screen so I blacked out the garage and passed the lead in through the window. I had marked out a number of viewing locations with chalk dots (the reflector has an equatorial mount, which needs correct alignment, so marking the required position of the tripod legs well before the event saved a lot of time!) and hoped to view almost the entire event as the trees weren't so much of a problem (not after a bit of surreptitious pruning, anyway!). Whether I would be able to capture the passage of Venus onto the sun's disc (1st & 2nd contact) was not certain though as the garden wall threatened to intrude: only time would tell!

Rising at 5:45am I was relieved to see a cloudless sky, and luckily this persisted throughout the morning with only a few wisps of high cloud. My preparations all proved to have paid dividends and I was very glad to see the shadow of the garden wall clear the reflector tube at around 6:10am. Bearing in mind the relatively slow progress of Venus across the sun I had decided to take one photo every 10mins with each of the cameras, offset by 5mins relative to each other. This meant I was dashing from the house to the garage and back almost continuously for over 3hrs in the hot sun! The web-cam didn't always behave itself but on the whole I was pleased with the outcome. The projection screen worked very well and I was able to take a good set of well-aligned shots with few difficulties. In both cases little computer manipulation was required apart from contrast adjustment and image rotation, but due to the number of images taken (about 125 in total) it all took rather a long time! For further details as to how I achieved all this, see the Technical Info page.

Although the next transit is actually on 6th June 2012, only the very end will be visible at sunrise from England (the same is true in 2117) so if you missed this transit I'm afraid you've blown it as your next opportunity won't be until 8th December 2125!