Last night, at 22:51 EDT, I went outside to observe a Tiangong-1 pass (the first Chinese space station). It was expected to peak at a magnitude of 1.5, which is moderately bright. However, I had a big surprise because it actually became very, very bright before it entered the shadow. I'd estimate the magnitude as a negative one (-1 or -2 maybe). There was no expected iridium flare in the area and the space station went eastwards.
How could it become so much brighter than expected?