06:19 There hasn't been a Transit of Venus for 121½ years.
06:20 Hang on, yes there has.
06:21 Just for once the sky above London is blue and virtually cloudless. Perfect.
06:25 Breakfast TV is showing live pictures with a tiny bite taken out of the left-hand edge of the Sun.
06:32 More than half of Venus is now visible on the solar disc...
06:40 ..and now all of Venus is on board. No sign of the notorious 'black drop effect' (a blurry edge where the shadow of Venus merges with the edge of the Sun)
06:50 Venus is well on its way on this rarest of journeys, with just over five hours until it reaches the opposite edge of the Sun.
07:25 My first attempt to view the transit. I'm off outside with the special viewing glasses I got for the 1999 solar eclipse.
07:50 No luck. A perfect view of the Sun, but my naked eye couldn't quite make out a tiny Venus-sized spot. I tried to convince myself that the Sun was slightly darker in the bottom left corner but I saw nothing conclusive. I do look very fetching in luminous orange cardboard spectacles though (and please don't try this without).
08:25 My second attempt to view the transit. I'm off outside with the two bits of cardboard to try to make a pinhole camera.
08:40 No good at all. Can't focus the image.
08:45 The BBC are reporting live from the Greenwich observatory. Various D-list celebrities (including the legendary Jon Tickle) are viewing the transit using some rather more impressive kit.
09:00 My third attempt to view the transit. I'm off outside with a pair of binoculars (one eyepiece blocked off) and a piece of card to project the image onto.
09:10 No good either. I did manage to project a circle of light onto the card but I suspect the dots I saw were specks of dust on the lens, not a passing planet.
09:22 Exactly halfway through now.
09:30 I tried my solar glasses again and... success! There's a little black spot on the Sun today. It's very small but it's most definitely there, just up from the bottom and slightly to the right. Absolutely insignificant, and absolutely fantastic.
10:10 I'm heading off to Greenwich to see what I can see from there...
11:15Greenwich Observatory is heaving with people, telescopes and TV crews. Amateur astronomers have gathered in the courtyard to view the transit using a variety of instruments, and the public are queueing up to take a look through the various eyepieces. There are free solar specs for all, and classes of children on very special school trips are gawping heavenward. Adam Hart-Davis is pre-recording chunks of tonight's TV programme from a fenced-off area by the car park.
11:30 I look into a proper telescope and see a perfect black circle silhouetted against the surface of the Sun. Wow.
11:55 I'm now looking into my third telescope, the Flamsteed Society's special 'Coronado'. Venus is very close to the edge of the solar disc, its image appearing inverted to the top left of the eyepiece. To the left right I can also see a giant orange flare burning off the side of the Sun.
12:04 Venus touches the edge of the Sun - third contact. I'm watching the planet's wobbly shadow projected inside a special cardboard box called a Solarscope. And the photo to the right is my contribution to international astronomy.
12:16 My last look into a telescope, with Venus now just a tiny semi-circular bite out of the edge of the Sun.
12:21 Watch the shadow disappear on the Solarscope. Is it still there? I think so.
12:23 No, it's gone. A cheer goes up from the assembled astronomers.
12:24 And that was it, the transit is over. Viewing conditions could hardly have been better, and it's been a memorable experience for all present and everyone else watching around the world. View some pictures of the transit of Venus here. Your next chance to see one will be on 6 June 2012, but from the UK you'll only see the final moments low in the sky just before dawn. Today's shadow play, I have to say, was a once-in-a-lifetime spectacle.