An asteroid the length of six football pitches is hurtling towards Earth.
The huge rock, called 2004 BL86 by astronomers, will sweep safely past the globe later today.
A spokesman for Nasa said: “It 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.”
If there are clear skies, amateur astronomers with small telescopes and strong binoculars should be able to see the asteroid from their own garden at 12.44am between Jupiter and the star Procyon.
It will pass about 745,000 miles from the Earth’s surface. For comparison, the moon is about 240,000 miles from Earth.
The next time a space rock this size flies past Earth will be in 2027.