How fast must an object be moving before it becomes imperceptible to humans (pt 2)?

Alright, lets try again with more detail. The object in motion is roughly the size of an adult male human, and the distance from the observer is roughly 5000 feet.How fast must an object be moving before it becomes imperceptible to humans (pt 2)?
5000ft is nearly a mile, I doubt you could even see a stationary person at that distance.How fast must an object be moving before it becomes imperceptible to humans (pt 2)?
You would have a hard time seeing a person standing 5000 feet away. If he was moving, he would be easier to see, not harder. For something that big to be imperceptible, it would have to be moving impossibly fast, like ten thousand feet per second, or maybe more. It would have to fly across your field of vision in a fraction of a second, and your field of vision would be around 5000 ft. wide.


Think of a guided missile the size of a man, flying at 3000 ft/sec. (Assume there is no contrail.) Would you see it at 5000 ft? You should if you are looking in the right direction, although you would only see it for a second or two.
Ok, it seems the resolution of the human eye in good light is about 81MP or 1.6 minutes of arc. (0.027 degrees). A two-foot wide person standing 5,000 feet away would be about .022 degrees, (2*arcTan(1/5000)) so it would be difficult already.


Temporally, the maximum flicker rate we see is something like 75Hz, or 0.0133 seconds. So you could guess that something that passes your entire field of vision in less than 0.0133 seconds might go unnoticed, but your field of vision is a tad more than 180 degrees, so you would see anything travelling in a straight line fade into the distance.


So here's a guess - 120 degrees view in 0.0133 seconds, so something circling your head a 9022deg/sec, or 1,504rpm shouldn't be visible at any distance. But you might still feel and hear it. At that rate, it would break the sound barrier at 27 inches away or more - my guess is you would hear that.
This question has a lot of variability. If the object is about a mile away it would be difficult to observe standing still. I would imagine a motorcycle on a highway a mile away traveling 70 mph would have a good to fair observability. Twice that speed fair to poor. I will take an educated guess and say 400 - 500 mph, maybe even more. It really depends on the surrounding and the amount of light reflected from the object.