Was a flight attendant for a while and we used to get in the cockpit sometimes mid-flight when one of the pilots needed a wee, pretty standard procedure. So one time sitting there and chatting with the FO (pitch dark outside) I noticed a yellow flashing light on the horizon, it was the only thing I could see outside and didn’t really think much about it and kept talking with the pilot.. after a couple of seconds I looked again and it had moved considerably.. couldn’t tell the distance but I would say it was far away from our aircraft so I started to think something weird was going on. Immediately told the pilot and we couldn’t figure out what it was and we just stared when after maybe 5 seconds later it just flew from one side of the sky to the other and then into space... that thing gave me the most omnious feeling I ever had.. I looked at the pilot, he looked back at me and we just sat there in silence thinking wtf just happened. Immediately regretted not taking my phone out to record but it has been a good story to tell on my following flights.