both infrafred and uv are in the ligth spectrum. they are just outside our sight spectrum. which bring us to the question of ufo's that appear on infrared and uv cameras but cannot be seen by the bare human eye. assuming they are made of solid material. it shows that material emitting light outside our sight spectrum appear translucent to our eyes..  interestink.. as we could have that material right on this planet but have not discovered it yet because we simply can not see it. this same material could be responsible for gravity.  that or they manage to "cloak" themselves by engulfing themselves with uv/ir light drowning out human sightspectrum frequencies..
Kekistani