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The moon is the Earth’s satellite and the Blue Planet’s gravity should keep it perfectly in its orbit, that’s what logic says. But the moon has an inexplicably loony, eccentric orbit. Now, a new study of the moon’s orbital history has shown that Earth’s sister planet, Venus and gas giant Jupiter takes turns to tug at the moon on rare occasions when their distant and puny gravitational tugs can have an effect. The idea that these far-off planets could affect the moon would seem far-fetched since the gravity of those planets, at tens of millions of miles away, is miniscule. However, Matija Cuk of the University of British Columbia has worked out the details of those times when the moon’s orbit and the orbits of Venus and Jupiter are in synch, and found that over the eons with repeated tugs, the two planets could have cumulative effects. "These ‘resonance’ effects have pulled the moon out of its circular orbit and elongated it. This is the first time that anyone has shown that the moon is affected by other planets in major ways," said Cuk. Doug Hamilton of the University of Maryland said a good way to visualise the process is to think of an adult pushing a child on a swing. "If you stand behind the child and gently push at the right times and the child swings their legs in synch, they go higher and higher. But if you push from the side, in any direction with no rhythm, there is no cumulative effect; no swinging and you get a frustrated kid," Discovery News quoted Hamilton as saying. Cuk said what brought the moon into synch with Jupiter and Venus, at different times, was Earth’s oceans. The constant tidal tug-of-war between the oceans and the moon caused the latter to recede further from Earth, gradually increasing the time it took to complete an orbit. It also made the moon’s orbit more circular, said Cuk. "But as the lengthening time period of a lunar orbit increased, it crossed into long episodes of resonance with Jupiter and then Venus. The tiny pushes upset the moon’s neat circular path, making it the elongated orbit we see today," he said. The study appears in the October 12 issue of the journal Science. — ANI
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