Sorry to all the astronomers out there; I take it back. I've just read up a little more on 2002 UB313 or Sedna as it's now being called, and done a few calculations.
The Earth's moon is about 382,480km away from Earth and 3,476km in diameter. (Interestingly, the Shuttle would have to go 400 times higher than its current altitude to get to the moon.) Resorting back to the good ol' inverse tan function, this means that the angle that your eyes would move between looking at the left-hand edge of the moon and the right-hand edge is around 0.52°, or 0.009 radians. Put another way, if you were out at sea (with a full 180° sky), you'd need 346 moons in a string to go from one horizon to the diametrically opposite horizon.
Now take our new friend Sedna. It's less than 1,700km in diameter and is currently 13,000,000,000km away from us. That means that its equivalent angle is 0.00000749° or 0.00000013 radians, so you'd need 48,047,887 of them to stretch in an arc across the sky. In other words, visually, it is 69,425 times smaller (in terms of width, not area) than the moon.
If you chose to look through your telescope at night, assuming you're on the correct side of the earth at the time, if you chose a single point at random to look at in space, there would be a 467,621,956,521,874 to 1 chance that you'd be looking at Sedna.
Well done for finding it!
