Keep an open mind folks!
A lot of comments in this post are basing assumptions on our own level of civilization, like saying if there was aliens and they had come all this long way here they would just sit in the sky and disappear. Who says they would need that long? The universe is so old, it is easily possible that there are civilizations that had thousands, if not hundreds of thousand years more in advancement in technology and consciousness. Just imagine where we would be in 1000 years. And principles of physics are regularly being discovered as not the full truth we thought. It would be ignorant to believe we know it all and we can say these things with such certainty.
On another note, sadly there is much ridicule still present in the mind of people, like seen also in this thread. This is a subject that deserves true investigation and let me tell you that the ridicule was instigated by the CIA in the late 40s in a period where UFO mass sightings became a regular occurence in the USA. Because the government didn't know how to explain it they chose to ridicule it, because to ridiucle something is the BEST WAY to keep people from thinking and talking about something, because they won't take it serious anymore.
I mean, they truly succeeded, think about it. Most of you just laugh about without ever giving it true invesitgation and own tought. While the facts are that if you just dig a little bit, you quickly discover serious implications. Like high-ranking government officials that have been outspoken about the subject. If you don't trust regular folks and their UFO reports, would you rather trust a military general, or an astronaut? How bout a secretary of defense?
Do your digging, but here are some nuggets:
Astronauts:
Brian O'Leary https://www.youtube.com/watch?v=PraLm46PHHs
Edgar Mitchell: https://www.youtube.com/watch?v=7AAJ34_NMcI
Gordon Cooper https://www.youtube.com/watch?v=dvPR8T1o3Dc
Former Canadian Secretary of Defense, Paul Hellyer
https://www.youtube.com/watch?v=2QwInlHmX-o
National Press club 2010, high-ranking officials state their experiences:
https://www.youtube.com/watch?v=3jUU4Z8QdHI