Yarkovsky effect
During WT1190F's orbit, it changed significantly in brightness, from an apparent magnitude 16 at perigee, to magnitude 23 at apogee. It spent most of its time dimmer than magnitude 20. This, combined with solar pressure acceleration, the Yarkovsky effect, and frequent orbital perturbations by the Moon, made it difficult to precisely predict its orbit and location. About one hour before atmospheric entry, the object had a R magnitude of 13.6, roughly the brightness of Pluto.