An asteroid half-a-kilometre in diameter will pass close by the earth on January 26, Australia Day.
The space rock, code-named 2004 BL86, is expected to reach a point about 1,198,705km from our planet, or three times the distance to the moon.
Although easily far enough away to be safe, the flyby counts as a narrow encounter in astronomical terms.
It will be the closest any asteroid comes to the earth until the predicted fly-past of another rock, 1999 AN10, on August 7, 2027.
Latest estimates suggest that AN10, which is 965 metres across, could approach as close as 30,570km.
Dr Don Yeomans, retiring head of the US space agency NASA's Near-Earth Object Program office at the jet propulsion laboratory in Pasadena, California, said: "Monday January 26 will be the closest asteroid 2004 BL86 will get to earth for at least the next 200 years.
"And while it poses no threat to earth for the foreseeable future, it's a relatively close approach by a relatively large asteroid, so it provides us a unique opportunity to observe and learn more."
The asteroid is likely to be bright enough for amateur astronomers to spot with small telescopes and strong binoculars.
"I may grab my favourite binoculars and give it a shot myself," Dr Yeomans said.
"Asteroids are something special. Not only did asteroids provide earth with the building blocks of life and much of its water, but in the future, they will become valuable resources for mineral ores and other vital natural resources. They will also become the fuelling stops for humanity as we continue to explore our solar system."
The asteroid was discovered on January 30, 2004, by astronomers operating the Lincoln Near-Earth Asteroid Research survey telescope in White Sands, New Mexico, US.
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