As to UFO... it doesn't have to mean alien. Literally anything in the air could be a UFO until it is identified. That doesn't mean it is something mysterious.

I've seen some weird things in the air before that I couldn't explain, but they were not there long enough for me or the others with me to really get a chance to explain them.

My case some friends and I thought the moon was awefully low and we could see some trees behind it. We did a double take it was still there, looked at each other, looked back and it was gone. No clue what it was and don't even want to speculate.

All I know is the moon rose a few hours later from behind the mountains on the opposite side of the sky.

So that was in the air and was Unidentified. It wasn't there for long enough for us to really stare at it long and try to determine what it was. Very likely some natural explanation, and that is the only experience of that kind I've personally ever had.

So you said you discount UFOs. I think that is false. Anytime you see something in the sky that you can't identify it is technically a UFO. You likely simply do not believe the alien visitors, flying saucer, time travel machine, type stories.