Every one likes a good UFO
tale and not a few out there like to think that benevolent aliens have been
watching over us, visiting us for thousands of years and helping us along the way.
But what if they didn't? Not to say we are alone out here in the universe, not at all.
The very fact they haven't visited shows the good sense of an advanced culture that knows better than to come to this violent world, where we shoot first and ask questions later. [see almost any scifi movie and you will know what I mean.]
So, if it's not them then who?
well, once you have taken the obvious out of the equation, what is left must be the truth.
Regardless of who says time travel is not possible, it must be us. Why? Even with the probable rules laid down prior to visitation to another time, there are always humans who will buck the system. And so, sightings.
"experts" say there is no time travel because no one has walked up to them and said "why, Hello, I am a time traveler here to observe you".
No doubt the vehicle of choices for bopping about the rangy planet at times when you cant just blend in, or need to get somewhere fast, was probably the saucer we so often see. I would imagine that by now, they know they have been seen, as they know we are talking about extraterrestrials at a regular rate, and they must know its them we have seen, so I would imagine that some of the craft being used would have to flying objects that we would not notice, like a plane. There are so many of them in the sky night and day, whats one more. But I would think, for the most part, they get into "costume" and have cash that is appropriate for our time and speak the lingo as a seasoned current traveler might try to do now when vacationing in a foreign land. A different time would fit that criterion. I can also imagine a bit of Pygmalion taking place when they see primitive races struggling about trying to do things the hard way, and may have assisted, providing god like figures to those folks, who have passed that down through myth and religion to us. And lets admit it, it would be a gas to do what they do, right? Just about everyone who has ever watched Ghost busters knows, if someone asks "are you a God?" you gotta say yes or face the music.