red light crossing the sky on the shorelineI had just returned to my house from walking my dog on the beach when I noticed a red light above my house. So I decided to go up to the balcony, and then that's when I realized the light was crossing the sky, from north to south, on the shoreline, completely silent.My house is about 250 meters (273 yards) from the shore.This was not a red light from an airplane's navigation lights.This red light would get very intense and then would grow dimmer but wouldn't entirely disappear, unlike an airplane's red navigation light which basically seem to blink.This was not an airplane, I'm very certain of that. Planes crossing the Atlantic, arriving at Lisbon's International Airport usually do their approach exactly over the area where I live so I'm very used to watching them and I recognize their navigation lights.I can say for certain that it wasn't a (conventional) plane because the light was completely different, it was much lower than a plane, and it crossed the sky alot quicker than a plane, as it completely disappeared from my sight in about 1-2 minutes.At the time of the sighting there wes a civilian plane on the sky, so besides the obvious differences I also had real time comparison with an actual plane.I called the Portuguese Air Force 30 minutes after the sighting and told them what I had seen, and they were very helpful and asked me the (I assume) usual questions: estimated altitude of the object, duration of the sighting, etc. and told me they would get back to me.They did, 10 minutes after that, and the person told me he had contacted civilian and military airtraffic controllers and they didn't saw anything on radar.I'm sorry I didn't took any pictures or recorded the sighting, but even if I had a camera with me, I don't think I would have anyway, since it didn't even crossed my mind long after the sighting was done. I was just mind blown looking at it.