The path of asteroid 2012 DA14 across the south-west sky as seen from Sydney on the morning of Saturday 16 February 2013. The times indicated are in AEDT while the positions with relation to the horizon are calculated for 5:00 am. Diagram Nick Lomb

On the morning of 16 February 2013 (Australian time) 2012 DA14, a piece of space rock the size of a large city building, will hurtle past the Earth at a speed of about 28,000 km per hour. Its closest distance to the surface of the Earth will be about 27,700 km, which is closer than any other similar object in modern times. That closest approach is within the paths of the geosynchronous communication satellites that circle at 35,800 km above the equator. However, there is no likelihood of 2012 DA14 hitting the Earth and little chance of a collision with a satellite.

An illustration showing how 2012 DA14 will pass by the Earth and its system of artificial satellites. Courtesy NASA

It will be possible to see and photograph this rare close approach, but from Sydney it will be a little tricky. As the rock is heading for its closest approach rendezvous at 6:26 am AEDT and brightening as it comes closer, the Sydney sky is also brightening with the coming of dawn and sunrise. Any view of the space rock or asteroid is likely to be lost after nautical twilight at 5:34 am when the object’s predicted brightness is 8.2 mag (see discussion on magnitudes below). At closest approach, which almost coincides with sunrise in Sydney, the prediction is for a relatively bright 6.9 mag.

Those who fancy a trip to Adelaide or even to Perth will have a better opportunity to see the flypast at its closest for the Sun rises later there. Of course, as usual with astronomical events the best viewing is from a dark sky site, away from city lights.

For those not familiar with the magnitude scale used by astronomers, it is a measure of the brightness of stars and other objects in the sky. It works in reverse to what you may expect in that the fainter a star the greater its magnitude. Venus, for example, can be magnitude -4, the brightest star has a magnitude of about -1, the faintest star visible from a suburban location maybe magnitude 4, the faintest star visible from a dark location maybe magnitude 6 and with binoculars from a dark sky magnitude 9 maybe visible.

Those in a dark sky should be able to see 2012 DA14 with a pair of binoculars just before dawn. From Sydney suburbs a Go To telescope could be sent to the exact celestial coordinates of the object courtesy of JPL’s Horizons service:

4:00 am AEST RA 10 08 34.75 Dec -76 18 35.2
4:30 am AEST RA 10 29 03.10 Dec -69 26 18.5
5:00 am AEST RA 10 43 14.02 Dec -59 11 15.1
5:30 am AEST RA 10 53 41.53 Dec -43 38 41.4
6:00 am AEST RA 11 01 43.36 Dec -21 21 32.2

For most people though the best way to attempt observation is to set up a camera on a tripod, or better still, a tracking mount pointing in the region of the sky below the Southern Cross and take time exposures during the period between 5:00 and 5:30 am from Sydney (or until local nautical twilight at places to the west of Sydney). If the exposures are long enough the space rock may appear as a faint streak longer than the shorter streaks from stars.

The observations and imaging may not work, but it is still worth trying if the sky is clear. It is a long wait until the next such close pass that we know about, which is that of the asteroid Apophis on 14 April 2029, again in the morning sky. What have you to lose? Only a little bit of sleep!

Nick Lomb

This post has been published simultaneously on the Sydney Observatory blog.