A 900 foot-wide asteroid will make the latest in a series of close approaches to the Earth tomorrow.
Scientists have ruled out any possibility of a cataclysmic collision - yet - but there remains a non-negligible chance of the asteroid Apophis smashing into Earth in 2036.
This year Apophis, named after an Egyptian mythological demon, will not get closer than around nine million miles.
Scientists will use the encounter to improve their estimate of just how dangerous the space rock really is.
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.
Current models predict a tiny but real likelihood of Apophis colliding with the Earth in 2036.
When the asteroid was discovered in 2004 scientists calculated a one-in-45 chance of an impact in 2029. Improved predictions later lifted the threat.
The asteroid's latest near approach will occur at midnight Irish time.
Members of the public can view the 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."
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.
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