I was doing some thinking as to whether aliens are really out there. Then I figured, they probably don't want us to find them if they are out there, so they are probably hiding (and maybe a little even embarrassed by us as a species). Then I thought, "How exactly would one go about hiding a planet from humans?". The answer I came up with is, is to make the planet travel faster than the human eye can see. This can be done by either speeding up the planets rotation on its own axis (probably easiest) or by increasing the velocity of its orbit around whatever is it is orbiting. Anyways, assuming this is possible (I dunno, maybe the aliens are ethereal and don't really need to bother with gravity), I was left with a final question. Exactly how fast does an object need to travel before it vanishes from human sight? Immediately I thought to myself, "Hmmm...what moves so fast I can't see....Oh yeah, magician slight-of-hand tricks....Hmmm, exactly how fast are those magician's hands moving?" I remember reading somewhere that the fastest baseball pitched was clocked at around 100 miles per hour, so I assume the magicians are moving their hands around that speed. Then I thought, hmmm...."why is it that I can't see a magician hands moving at 100mph yet, I can see a Boeing jet pretty clearly moving 550mph". Putting two and two together, I concluded, that that velocity at which an object must travel so that is dissapears from human sight is somehow proportional to the mass of that object. Thus, a planet would probably need to travel REALLY fast to disappear (unless its a tiny planet). Any thoughts?