London: An asteroid a third of a mile wide "narrowly" miss Earth on January 26.
The space rock, code-named 2004 BL86, is expected to reach a point about 745,000 miles from our planet, or three times the distance to the Moon.
Although easily far enough away to be safe, the flyby - at an estimated 35,000 miles per hour - counts as a close shave in astronomical terms.
It will be the closest any asteroid comes to Earth until the predicted fly-past of another rock, 1999 AN10, on August 7, 2027.
Dr Don Yeomans, the retiring head of the Nasa's near-Earth object programme 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."
Nasa's near-Earth object programme, also known as "Spaceguard", searches for objects that might potentially pose a hazard to the planet. The BL86 asteroid is likely to be bright enough for amateur astronomers to spot with small telescopes or strong binoculars.
Dr Edward Bloomer, an astronomer at the Royal Observatory Greenwich, said: "By nightfall on the 26th, the sun will be below the horizon and out of the way, giving you a good chance to look at asteroid.
"Or if you are looking on the morning of the 27th, you might have time to see it before the sun rises." He added: "The coast is a good place to go, as you are away from external sources of light."
Nasa's Deep Space Network antennae at Goldstone, California, and the Arecibo Observatory in Puerto Rico will be used to obtain science data and radar-generated images of the asteroid. It was discovered on Jan 30, 2004 by astronomers operating the Lincoln Near-Earth Asteroid Research (Linear) survey telescope in White Sands, New Mexico, US.
"Although this particular asteroid won't get so close again for 200 years, others like it will get equally close much sooner," said Lord Martin Rees, the Astonomer Royal. "The Earth would need to have more than 100 times its actual diameter if it were to hit."
