The Size of the Universe

I'M IN OXFORD at one of my favourite museums, the Oxford Natural History Museum. Apart from the fact that it is a beautiful building, it's also full of the most fascinating collections. I could spend weeks here, looking at all the fossils and crystals and bones... Every time I visit I find something new.

I just noticed this (see photo below) which seems oddly out of place here, amongst all the ammonites and sabre-toothed tigers, but maybe this is the perfect place for it, after all. There's a model of the sun sitting on the balcony. Nothing special, just a football-sized golden globe. But then on the opposite balcony is a case with a model of the Earth and the Moon, which are to scale in terms of size and distance from each other, and also to scale in terms of their distance to the sun model on the other side of the museum.

In the photo, I've tried to show all three. The Earth and moon are at the bottom, tiny dots – the Earth is the size of a petit pois pea – held on bits of wire; it's the dark area of the photo, with the circle showing the Moon's orbit. Now look across the gallery, between the third and fourth columns counting from the left, and you'll see a golden ball, the sun. That is to scale. Impressive, huh?

Next month, 4th August, a spacecraft will be making that trip. The Parker Solar Probe will be launched on a Delta IV Heavy and by 1 November it will make its first close pass, about 30 solar radii from the sun's surface, then getting closer and closer with each orbit until it's about 6km from the surface, and within the sun's atmosphere, the corona. I was impressed by that even before I saw the scale model of the distances involved.

There's one other fact that really blew me away though. At these scales, if we wanted to include Alpha Centauri, our nearest stellar neighbour, where do you reckon we would have to position the model star? Across town in the Ashmolean? No. How about where I'm staying, in Abingdon, a half-hour bus ride away? No. Okay, then, what about putting it in London, in the Science Museum, about 50 miles away? No, not even close. At these scales, we'd need to position our Alpha-Centauri model about 1 million kilometres away. That's about three times the distance of the Earth to the moon. And Alpha Centauri is our nearest star.

Oh yes. Space is big!

This has nothing to do with Alpha Centauri. It's a T Rex, and too cool to leave out.