2. What do asteroids look like in the sky?
Given a single image of a starfield, it would be virtually impossible to distinguish an asteroid from the stars. Indeed, the word asteroid basically means star-like. In addition, most asteroids are far enough away and therefore faint enough, that they are not obvious to observers, requiring telescopes and multiple observations to be seen.
Fig 1: 4 Vesta, taken by Tony Hoffman, 21 Jan 2006
So how can you tell there is an asteroid in the picture? Typically, asteroid observers will either take one long exposure -- tracking on the stars so the stars are still pinpoints, but any asteroids will trail -- or take multiple exposures with sufficient time in between. The images can then be stacked into one showing the multiple positions of the comet or combined into an animation that shows the motion of the comet.
Fig 4: Sketch of Vesta over a week. The first sketch was made on 8 Feb 1999 using an Orion 80mm Shorttube and 32mm Plössl eyepiece. The position of Vesta was marked and several field stars were also sketched. Observations were then made on subsequent nights. As Vesta moved out of the original field of view, stars were added for context.
Sketch made by Elizabeth Warner while working at USC's Melton Memorial Observatory.