Jetlagga

Jetlagga flies with a caesium clock in her backpack. East or west, it comes home not quite agreeing with the ground.

The Physics

In October 1971 four caesium-beam atomic clocks were flown around the world on airliners, once eastward and once westward. Speed slows a clock; height speeds it up. Earth's spin means the eastbound plane moves faster than the ground and the westbound one slower, so the two trips differ.

Observed: eastward −59 ± 10 ns, westward +273 ± 7 ns (predicted −40 ± 23 ns and +275 ± 21 ns)

• ns: nanoseconds, 10⁻⁹ s, clock gain (+) or loss (−) relative to the ground

J. C. Hafele and R. E. Keating flew the clocks in October 1971 and published in Science in 1972.

On the shirt

Front: Jetlagga, the pixel-art character, with the title. Back: the observed-versus-predicted table, the speed-and-height explanation and the Science papers. Printed on a unisex tee.