Crossing the Thames at the speed of light

Last night I returned from an excellent couple of days in the Smoke. Not that there's much actual smoke in London these days - what there is seems to come mainly from the chimneys of narrowboats!

I alighted from the train with my new folding bike at Stratford and found a machine where I could top up my Oyster card. It's a good job I did as there was only £1.80 left on it. Then I took a Jubilee Line train to North Greenwich, where David met me on his bike. We cycled to his house the scenic route along the Thames Path. The green laser beam shone out from the Royal Observatory at Greenwich along the meridian.

There was just the right amount of moisture in the air for the beam to show up clearly: too much mist and the beam would quickly get scattered; too pure an atmosphere and the beam would be invisible.

We criss-crossed the meridian several times that evening - here we are within a few feet of it.

I wondered about the wisdom of having the beam pointing up into the sky - what if it blinded aeroplane pilots?

But when you climb up to the observatory itself you see that the laser actually points approximately horizontally to the other side of town. It shoots out of the side of the building ...

... and whizzes past Greenwich Power Station (a stand-by generator for the Underground) and the O2 Arena (formerly known as the Millennium Dome) before crossing the Thames to Blackwall and the River Lea.

And all at 300 million metres per second.

Photographs of the London nightscape are irresistible, aren't they? Click on the photos to see larger versions, and spot the laser beam.

I'm standing under it again here: the beam is coming over my head from top to bottom in this photo, taken from the vantage point of Greenwich Park.

In a later post I'll talk about my adventures with Indigo Dream. Those Woolwich Ferries are big!