An asteroid capable of destroying a city the size of London will skim past the Earth on Friday, approaching closer than many satellites.
Scientists say they are sure there is no chance of the 45.7 meter-wide space rock hitting the planet.
But there is a remote possibility that it could collide with one of more than 100 telecommunication and weather satellites in fixed orbits above the Earth.
The asteroid, 2012 DA14, has been closely tracked since its discovery a year ago.
It is predicted to reach its nearest point to the Earth at around 7.30pm on Friday.
Experts have calculated it will stay at least 27,000 kilometres away -- easily far enough to be safe, but a very close shave in astronomical terms. Scientists have never observed such a narrow miss before.
Through binoculars, the object should be visible as a tiny dot of light crossing the sky.
Astronomer and asteroid expert Dr Dan Brown from Nottingham Trent University said: "It will be too faint for the naked eye but with binoculars it should be visible if you know where to look. It will be low to the north-eastern horizon and moving quite quickly.
DA14 belongs to a dangerous family of near-Earth objects (NEOs) that are small enough to be missed but large enough to cause serious damage.
It was detected in February last year by La Sagra Observatory in Spain as it fell under the spotlight of the sun's rays.
Travelling at between 20,000 and 30,000 kmh -- eight times the speed of a rifle bullet -- the asteroid will fly inside the orbits of satellites some 35,000 kilometres above the Earth.
"These are the satellites that provide us with telecommunications and weather forecasts," said Dr Brown.
"There are loads of them but you're talking about a very big area. It would be very unlucky if a satellite was hit."
The asteroid will pose no danger to the International Space Station, which orbits at an altitude of only a few hundred kilometres.