Why would a group advanced enough to travel such distances be witnessed by human eyes?
We have satalites with technology which allows them to read pages on a book from space right on Earth.
Any civilisation which can travel the distances required to visit earth would have analyitical technology that you can't even comprehend.
Therefore I believe your stance to be false
LOL...
They might have incredible abilities to travel distances, etc. But when it comes to floating in one place for a certain amount of time, I believe that radar likely gets them, if only because they don't feel the need to hide from radar (meaning they could hide if it meant their survival, but I don't believe we fck with them)
If there are aliens, our air defense knows it. The things following the shuttles, the things moving thru the shots on space missions, whatever they are (manmade tracking devices or alien craft), our govts know about them. Some of the Eur govts have admitted a great deal aobut aliens, haven't they? I remember soemthing about some govts no longer hiding what they know.
At the same time, most americans didn't conceptualize an atomic bomb until we gave hiroshima a bitchslap. So whatever other technologies we've been working on, well, it might be easy to blame it on aliens. We proabbly have some pretty gangster flying craft in the arsenal that even our local yokel military men can't conceptualize.