A large asteroid is set to pass Earth in a close encounter which scientists say will pose no danger.
The asteroid, estimated at half a mile (800m) wide, will sweep within 270,000 miles (433,000km) of the planet - only slightly further away than the moon.
"It's not Earth-threatening," said Don Yeomans, who heads Nasa's Near Earth Object Program.
The asteroid, 2004 XP14, should be visible by telescope from N America and Europe, most clearly on Monday.
"For something of this size to come this close is unusual"
Asteroid-spotters should look towards the Perseus, Cassiopeia and Cephus, constellations to try to spot it.
It will appear as a moving dot against the stars, said Roger Sinnott, of Sky and Telescope magazine.
The asteroid is expected to pass the Earth on a number of future occasions too, but scientists believe it is likely to be further away on future passes.
The asteroid, which was discovered in 2004, is one of the largest of several dozen asteroids to have passed near Earth in recent years.
"For something of this size to come this close is unusual," Mr Yeomans said.
US scientists will use a radar beacon at the Goldstone Observatory in the Mojave Desert to work out more about the asteroid's shape, and about its likely future course.
It is among 783 asteroids currently classified as potentially hazardous by the Minor Planet Centre in Cambridge, Massachusetts, because of its size and proximity to Earth.
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