MOONWALKING astronauts often lost their balance, but they weren鈥檛 clumsy 鈥� it was gravity鈥檚 fault. It turns out that the moon鈥檚 gravity is not enough to help them distinguish up from down.
Laurence Harris of York University in Toronto, Canada, and his colleagues spun volunteers on a giant rotating arm to simulate different strength gravitational fields. As the volunteers spun, they saw images of a landscape or the letter 鈥減鈥�, which they read as a 鈥減鈥� or a 鈥渄鈥�, depending on which way they felt was up.
The study shows that humans need to feel at least 15 per cent of the gravitational force on Earth to figure out which way is up (PLoS One, ). The moon鈥檚 gravity is 17 per cent of Earth鈥檚, but it is also a strange environment; low gravity and unusual scenery explain why astronauts fell down even though they didn鈥檛 report feeling out of sorts.
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This article appeared in print under the headline 鈥淔eel the gravity to tell which way is up鈥�