Transit of Mercury

On the morning of Wednesday 7th May 2003 the planet Mercury, pictured left, was in transit (or passage) across the face of the Sun. Such an event is quite a rare occurence: there are, on average, only 13 transits of Mercury per century. Due to the particular orientation of Mercury's orbit, these all fall within several days of 8th May and 10th November: those in May are relatively less common (by a factor of two) but the planet's disc is 44% larger in area as its elliptical orbit takes it farther from the sun (and therefore nearer the Earth). We thus had the optimum conditions for observing the event.

The transit was due to start at about 6:15BST in England, be of maximum extent at around 9 o'clock and end at 11:30. I had determined in advance that the only convenient viewing positions at my home had the sun obscured by trees until about 9:30am, so I was able to get up at a reasonable time and still capture the second half of the event. I hung a pair of curtains in an open doorway, positioned the telescope through the curtains (secured with pegs!), and projected the sun's image onto a sheet of grey card supported on a chair. Although somewhat make-shift, this arrangement actually worked very well (though it confused the cats somewhat!).

I took almost an entire reel of film during the transit, using a standard 35mm camera and a variety of lenses (both "standard" and close-up). These shots came out acceptably well, but had various geometric distortions due to the angle at which they were taken relative to the card. These were corrected by computer manipulation and the resultant images rotated to a common orientation so that composites could be made (in order to show the progress of the transit). For further details as to how I achieved all this, see the Technical Info page.

If you missed this transit, your next opportunity is not until 9th May 2016! [There was actually a transit on 8th November 2006, but this was not visible from England.] The one after that, on 11th November 2019, will be of unusually long duration as Mercury will pass very close to the centre of the sun. In the meantime, the first transit of Venus since 1882 occurred on 8th June 2004. This was much easier to observe, as Venus is considerably larger than Mercury and much nearer the Earth and in fact it was visible to the naked eye (using suitable protection, of course) so direct photography would have been possible. I used two telescopes: a refractor to project the image (as per the Mercury transit) and a reflector fitted with a digital camera. To see how I got on, click here.