900 foot-wide asteroid to pass by Earth tonight

The asteroid will not get closer than around nine million miles to Earth tonight, they said.

Scientists will use this encounter to improve their estimate of just how dangerous the space rock really is, the 'Daily Mail' reported.

In 2029, Apophis is expected to come uncomfortably close, brushing past the Earth at a distance of just 30,000 kilometres. That will put the asteroid inside the orbit of communication satellites.

However, there remains a non-negligible chance of the asteroid smashing into Earth in 2036.

Public can view this unique event online via the Slooh web-based sky-watching service, which collects images from observatories around the world.

Slooh president Patrick Paolucci said, "Alone among all these near-Earth asteroids that have passed our way in recent years, Apophis has generated the most concern worldwide because of its extremely close approach in 2029 and potential impact, albeit small, in 2036."

We are excited to cover this asteroid live for the general public, he said.

While scientists at the American space agency NASA have calculated that if Apophis struck the Earth it would generate a blast equivalent to more than 500 megatons of TNT.

In comparison, the most powerful hydrogen bomb ever detonated, the Soviet Tsar Bomba, released 57 megatons.