Telescopes around the world will be watching over the next 24 hours as a giant asteroid skims past the Earth. The cosmic missile, which is estimated to be up to 2,000 ft long, will be closest at 8.33 UT at a distance of only 334,000 miles – less than one and a half times the distance of the Moon.

That is our closest shave with a large space rock for 22 years and will bring it close enough to be seen in amateur telescopes of 3-inches or more diameter.

The asteroid, cataloged as 2007 TU24, will appear to zip across the sky, covering three and a half degrees an hour – seven times faster than the Moon. It is predicted to become magnitude 10.3 at best so could also be a target for photographers.

By a strange coincidence, a second asteroid will have a near miss with our neighbouring planet Mars the following day, Wednesday January 30. At first, astronomers warned that 2007 WD5 could collide with the Red Planet but the odds of a collision have now dropped to just one in 10,000 and it is expected to miss by a distance of around 15,000 miles.

Amateur astronomers wanting to view TU24 will find useful advice plus a general chart at the Sky & Telescope site here. But as they point out, its apparent position against the stars will vary somewhat depending on where you are on Earth. The Society for Popular Astronomy have produced a map for UK observers.

Amateurs will not be the only ones watching, of course. Many professional telescopes are sure to be diverted from their usual science projects to study Earth’s close encounter. A giant radio dish at Arecibo, Puerto Rico, will bounce radar signals off TU24 to build up a map of its surface.

Another radio telescope, at Goldstone in California, has already taken the crude radar images shown here, revealing that TU24 has a very irregular shape.

The space rock is of a kind labelled a Potentially Hazardous Object, although there is no possibility of an impact with Earth in the near future. It was discovered on October 11, last year, by a robotic telescope scouring the heavens for Nasa to detect threatening asteroids.

Another asteroid, called Apophis, will have Earth in its sights twice in the next 30 years. In 2029, it will pass closer than Sky’s TV satellites. Experts fear that that near miss will put the 750 ft long asteroid on a collision course with our planet seven years later in 2036.

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