Based on its brightness, asteroid 2004 BL86 is estimated to be about 500 metres across. If it were sitting on the Earth, it would be as tall as Toronto's CN Tower.
At its closest approach at 11:19 ET, the huge space rock will be about 1.2 million kilometres (745,000 miles) from the Earth or about three times further away than the moon.
That's a safe distance, but closer than any other asteroid this big will come until 2027 – the year when we can expect a visit from another chunky rock called 1999 AN 10.
Slooh, a U.S.-based organization that streams celestial events online, will provide live images of the asteroid from telescopes in Australia starting 11 a.m. ET. It will also provide expert commentary from astronomers, including Paul Chodas, manager of the NASA Jet Propulsion Laboratory's Near-Earth Object Program Office, and invites questions via the Twitter hashtag #SloohBL86.
You may be able to see the asteroid this evening using strong binoculars or a small telescope, NASA says.
It will probably be easiest to find around 11 p.m. ET when it will be to the right of the planet Jupiter, between the constellations Leo and Gemini.
It will look like a slow moving star, said Randy Attwood, executive director of the Royal Astronomical Society of Canada, in an email.
NASA will also be watching the asteroid, capturing images and data, using its Deep Space Network antenna at Goldstone, Calif. And the Arecibo Observatory in Puerto Rico will also be following the close approach.
"At present, we know almost nothing about the asteroid, so there are bound to be surprises," said Lance Benner, principal investigator for Goldstone Solar System Radar, in a statement.
The asteroid was detected in 2004 and will not come this close to Earth for at least 200 years, NASA says.
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