Originally Posted by Killer
Asteroids are tracked by telescope, as they are too far away to be detected by radar. Because of this, they are observable only when illuminated by the sun against a dark background. If they are small and dark-colored, they are far more difficult to observe.
In the case of the Russian asteroid, it approached Earth with the sun behind it.
Cover-up continues - seems pretty obvious the cloaking device worked until the spaceship hit the atmosphere