Space rock 2012 DA14 is only 50 metres across. It will pass the Earth on Friday evening (UK time) just 17,100 miles above our heads. There is no danger of a collision. Nevertheless, this is closer to the Earth than many artificial satellites.

It will pass from the southern to northern hemisphere and set the record for the closest pass of any known asteroid since systematic surveys of the sky began in the mid-1990s.



Animated visibility map for asteroid 2012 DA14 between 18:00 and 21:30 GMT. The asteroid will be visible from green areas. Image: Geert Barentsen

According to Don Yeomans of Nasa's Near-Earth Object Observation Programme, an asteroid like 2012 DA14 flies this close on average only once every 40 years.

This time around, however, the next one is due sooner than that. On 13 April 2029, Apophis will pass Earth closer than the ring of geostationary satellites. But, at an estimated distance of 19,400 miles, it will not break the record set tonight.

As for 2012 DA14, this could be its last close pass. Earth's gravitational field will significantly alter the asteroid's orbit around the sun, reducing its orbital period from 368 to 317 days. This will mean most of its orbit will be inside that of Earth's.

The next time the asteroid draws near to us will not be until 2046, again on 15 February. Then it will only come to within about a million miles of our planet, or about four times further than the moon. So if you want to see 2012 DA14, this Friday is the night to try.

Nasa Television will broadcast a live webcast during closest approach on Friday, featuring commentary and images from telescopes around the world (if you are using a mobile device, click here). It will start at 19:00 GMT (19:00 UT, 14:00 EST, 11:00 PST).

Even though 2012 DA14 comes so close and is relatively large (about half the length of a football field), it is not going to become bright enough to be seen with the naked eye. Sky watchers can catch a glimpse of it using binoculars.

The object will be visible through binoculars for about four hours between 18:00 and 22:00 GMT. It is best seen from Australia, Asia and Europe and will be travelling quite quickly for a celestial object, crossing an area of the sky as wide as the full moon roughly every 30 seconds.



The BBC Sky at Night's Pete Lawrence offers this advice for locating the object from the UK: "The asteroid pops up above the eastern horizon at around 20:00 UT. It passes very close to the star 7 Comae Berenices at 20:17 UT so a good strategy is to locate this star and use it as a stakeout position, looking for a fainter dot passing by between 20:15 UT and 20:20 UT."

Shortly after 21:30 UT, 2012 DA14 will pass between two stars in the handle of the well-known constellation, The Plough (known to astronomers as Ursa Major). Although the asteroid will have faded somewhat, this offers another chance.

"Between 21:30 and 21:40, the asteroid crosses the line joining the stars Delta and Epsilon Ursae Majoris. The crossing point is roughly 2/5ths of the distance between Delta towards Epsilon and this is another good stakeout region," says Lawrence.

The Society for Popular Astronomy offers a comprehensive viewing guide.

Stuart Clark is the author of The Day Without Yesterday (Polygon)