It's Like Shooting at the Roman Colosseum

... and overshooting the Vatican.

Tomorrow Night (assuming you leave in Greenwich Mean Time), a 400 metre asteroid (2005 YU55) is passing within about 324 000 km (or 201 000 Miles) of Earth, the closest pass by any such object of comparable size until the year 2028.

It's not the largest asteroid to ever make such a pass (or even strike Earth), and certainly not the last, but unfortunately, conditions just wont be ideal for viewing. It will be too close to dusk, too close to the light thrown off by the moon, and generally too small to view with the naked eye or binoculars. A good telescope with a diameter of six inches or more might let you view it. For professional astronomers, this is an excellent opportunity to get images of the object at resolutions of up to two meters (that's per pixel.), or about the height of a fully grown adult male.

Now, I realize anyone who's been listening to me over the last few weeks (the lengthening nights always get me thinking about astronomy) is going to realize that 324 000 km is the width of an astronomical hair. It's closer than the mean orbit of the moon. But it's still like shooting at the Colosseum in Rome and missing by six kilometers (which, for reference, would take a fast person a little over an hour to walk. In point of fact, if you made that abysmal shot, you'd have shot closer to the Vatican City than to the Colosseum, in terms of what you managed to hit. It's still 324 000 km, regardless of whether or not it's small on an astronomical level.

For those of you lucky enough to own a sufficiently large telescope, enjoy. For me, well... I'll probably be studying for my accounting test.