Here's the comment I referred to.
Can it be a planet or Star a certain distance away from our Sun but in movement towards it so it "seems" to move slow?
The "stealth-mode" appearance can be the brightness of the solar flares replacing the light reflecting of the object so it seems invisible.
Off-course the question remains, what is it?
Seems plausible that it's an object that is moving away or moving toward .. which would give the impression of moving very slowly.. so it "could" be a comet or a meteor but it also could just be a type of lens flare effect on the optics
edit on 5/7/2012 by miniatus because: (no reason given)