A 150-foot-wide rock is about to make an unusually close pass by Earth. You might be able to follow it across the stars in a telescope — with exactly the right preparation.Expect a small asteroid to make big news on February 15, 2013. The gymnasium-sized rock 2012 DA14, 40 or 50 meters (130 to 160 feet) across, will make the closest Earth flyby of a natural object ever predicted well in advance. It will pass within 28,500 km (18,000 miles) of Earth’s surface around 19:25 Universal Time February 15th, reaching 8th magnitude as it whizzes north across the stars at a rate of 0.8° per minute.
But not for the Americas. At that time it will be near the head of Virgo, which will be up in a dark sky for longitudes from easternmost Europe (in late evening) across Asia to Australia (before dawn on the 16th local date).
By the time it can be seen from Western Europe it will be somewhat fainter. In North America, darkness won’t fall on the East Coast until several hours later, around 0h February 16th UT (7 p.m. February 15th Eastern Standard Time). By then the asteroid will be only magnitude 11.1 and moving much more slowly near the Little Dipper. By nightfall on the West Coast three hours later, it will have faded to 12.4.
The constellation chart at right shows, approximately, the asteroid’s race from practically the south to north celestial poles in just 12 hours. (Click here if you can't see the chart.)
But locating 2012 DA14 in a telescope will not be simple! It will be so close to us that your location on Earth will greatly affect its apparent path across the stars, due to parallax. And it will be near enough to Earth that Earth's gravity will rapidly alter its orbit.
To get an accurate prediction for your site including both of these corrections, go to the JPL Horizons ephemeris utility. For Target Body enter 2012 DA14. For Observer Location enter your latitude and longitude to 1° or better. For Time Span enter your planned observing start and stop times in UT and a Step Size of 1 minute. In Table Settings include Astrometric RA and Dec., as well as Visual Mag. Click "Use Selected Settings" when you're done with each entry, then "Generate Ephemeris." You’ll get a custom list of minute-by-minute positions.Next, using a detailed sky-charting program, print out a star chart to an appropriately deep magnitude centered on one of those equinox-2000.0 RA and Dec points you got. Or plot your points on a deep, large-scale star atlas, such as Uranometria 2000.0. Be looking there with your scope at the correct minute.
Another option is to use the SkySafari Plus or Pro app (for iOS, Mac OS X, and Android), recently updated by Southern Stars to accurately predict the asteroid's path using correct physics.
Dodging a Hit
The last time I watched an asteroid pass close enough to show real-time motion in my 12.5-inch scope, I had the eerie feeling that we were definitely dodging a bullet — rather different from the usual all-is-peaceful observing experience. Astronomers estimate that if 2012 DA14 hit our atmosphere it would release 2.4 megatons of energy, comparable to the 1908 Tunguska event, which has been estimated at 3 to 20 megatons. Not a world-killer, and possibly even harmless over an empty ocean or Antarctica (given that it's coming almost straight out of the south), but you wouldn’t want to be anywhere nearby.
See also NASA's announcement.
Radar observations are planned — by the Very Large Array and by NASA's Goldstone station — to refine the asteroid's orbit and future path, determine its spin (and thus get an idea of how the Yarkovsky effect will influence its future trajectory), and to image it.
Watch DA14 Online
— On Friday the 15th, NASA's Jet Propulsion Laboratory plans video coverage starting at 2 p.m. EST (11 a.m. PST; 19:00 UT [GMT]).
— Bareket Observatory in Israel will track the asteroid with images updating every 30 to 60 seconds from a remote telescope, from 2:00 to 3:30 p.m. EST (19:00 to 20:30 UT).
— The Virtual Telescope Project in Europe plans live streaming starting at 5 p.m. EST (22:00 UT Feb. 15th).
— HD video of the asteroid crossing the stars will be streamed from the Clay Center Observatory in Brookline, Massachusetts, from 6 p.m. EST until 4 a.m. the next morning EST (3 p.m. to 1 a.m. PST, or 23:00 UT Feb. 15 to 9:00 UT Feb. 16):
— Programming including real-time video will be streamed by Slooh.com beginning at 9 p.m. EST (2:00 UT Feb. 16th).
— NASA's Marshall Space Flight Center will stream images from 9 p.m. to midnight EST (2:00 to 5:00 Feb. 16 UT).