Here's a good explainer on what you're actually seeing in the radar image: http://www.planetary.org/blogs/emily-lakdawalla/2011/3248.ht...

* The signal is emitted from a radar installation on the earth, and reflected back to another dish.

* Brightness is reflected signal strength. So surfaces that are perpendicular to us will reflect better. The less the surface normal points to us, the less reflection we see.

* Up/Down is Time axis. The points closer to us will return sooner than points farther away.

* Left/right is Doppler shift. Parts of the asteroid that are rotating away from us will show up on one side, parts rotating towards us will show up on the other side.

(this is the vertically oriented image).