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THE moon not only tugs at Earth’s oceans, it roils the atmosphere too.

Four decades ago, theorists predicted that the moon’s shadow during an eclipse creates a dense pocket of cold gas that plows through the atmosphere like a boat, creating V-shaped waves. Attempts to measure them had failed – until now.

In July 2009, during the longest eclipse calculated to occur in the coming century, of the National Central University in Taiwan turned on a network of 1400 GPS receivers across Taiwan and Japan. Signals from GPS satellites ricochet off ripples in the ionosphere – about 300 kilometres above ground – creating a time lag on their journey to the ground. Liu used computer programs to turn the lag into patterns that identify and locate the ripples.

An eclipse shadow is thought to leave a unique ship-like signature, with bow waves and a wake. Liu says he saw both in the GPS signals ().

of the University of New Brunswick in Canada says the find is interesting but more research is needed to confirm it.