The first time I saw the speck of light was either the 3rd or 4th of September at about 8:15pm. I was walking my dog out by the desert and I just happened to be starring at the sky. I noticed what I thought was a faint star on the southeast horizon moving. It was so faint that I wasnt sure if I had imagined it or not. I kept looking in the direction of the object but with more focus now and I found it again. It flew in a straight path heading nw. I would loose behind the clouds occasionally but then pick it up on the other side. I finally lost it in the glow of Tucsons city lights about 30 seconds after I first spotted it. I figured it wasnt an airplane because the light didnt flash and it appeared to be so high. It looked like the faintest of stars moving across the sky. I figured it must have been a satellite, however, I was told the next day that satellites appear stationary in the sky. Anyhow, 30 seconds or so seems like a long time so I waited for what I knew to be a plane to come into view just to time its flight across the sky. Once I found a plane it appeared to be much closer but still remained in my field of view well over a minute before I stopped timing it. Ive been looking in the sky every night since the 1st sighting and tonight I saw it again. This time I could only see it for 11 seconds and instead of loosing it in the lights of the city, it just disappeared. It was heading in the opposite direction and cleared a quarter of the sky in that time period. I tried to film it with my phone this time but it was too faint. As excited as I was to see it again, I started to wonder what the chances are that a person gets to see a UFO twice. I dont know what it was but Im very skeptical that it was a plane. However, I do live next to a military base so perhaps it was so high altitude spy plane whose afterburners were glowing like the SR71.