Line 'em up

Spending many hours on Chesil Beach watching over the little tern colony over the last two months, it was inevitable that at some point my jumbled mind would turn to the matter of how many pebbles form the 18 mile long shingle bank, and furthermore, how far would they reach if laid side by side in a row? I’m surely not the first person to embark on this particular avenue of displacement activity, but like a small, white, yellow-billed, fork-tailed seabird tenaciously holding onto a hard-won sand-eel in the teeth of a storm, I couldn’t drop it.

Working out how many pebbles was going to be tricky, but luckily someone has already estimated this as 180 billion according to the Chesil Beach and Fleet Lagoon website http://www.chesilbeach.org/ .  There has been some serious rounding-up there no doubt, but it certainly saves some laborious collecting of vital statistics and lengthy arithmetic, so let’s not argue.

As the website confirms, the pebbles range from fist-size to pea-size depending on which bit of the shingle bank you’re trudging over, so for simplicity I’ve opted for an average pebble size of 2 cm. I might not be correct in this assumption but it seemed right at the time.

So... lining them up, 180,000,000,000 x 2 cm gives a row of pebbles 3,600,000 km long, or 2,235,600 miles. NASA says that Earth’s equatorial circumference is 24,873.6 miles, which means that the carefully arranged row of theoretically-proportioned pebbles would wrap round this planet just under 90 times, which is rather more than I expected when I started contemplating this.

The folks at NASA also tell us that 238,712 miles is the average distance from Earth to the Moon. The column of pebbles would cover that distance approximately 9.3 times, although if I tried it my stack would probably get a bit unstable before it reached my knees, especially in the sort of wind we’ve been having out there on the beach during the tern-watching season. I suppose it's a bit late to suggest it as an olympic sport.

PS. Why stop at pebbles? The BTO estimates the upper limit of the European summer population of Little Terns as 41,000. If you could get them all to line up end to end without squabbling they would reach for about 5.85 miles, which is about 70% of the length of the Fleet lagoon.