I was lounging in my backyard pool. As I was floating on my back looking up at the stars I saw one large starlike object appear to be moving. I stood up to take a better look, I could not identify it as a plane. The large round light was about the size of Venus and was flying rather low and moved somewhat fast, like a jet speed. I thought if it was plane then perhaps it was getting ready to land at the Tucson International Airport.The "plane" had no red or green lights, just showed a steady white light and made no sound. So I settled in my pool noodle to follow it awhile. I was looking for blinking lights or red or green and saw none so then the light passed through a thin cloud and it dimmed a bit. But what got me to report this otherwise fairly benign light was that I watched it enter a lone, fluffy white cloud. The white cloud was lit up by the city lights, the cloud was smallish, compact and dense with well defined edges, I could easily see faint stars around the whole perimeter. There were no other clouds near it. So the punchline is this; The large, white, round light moving at a steady speed and in a straight path entered the small dense cloud and the "ufo" never appeared out the other side. I watched for it to reappear for a solid 7 minutes to cover all possible angles it could have taken. I watched so long the cloud was eventually pulled apart by winds. By the time I gave up looking for the light the cloud was less dense and rather wispy. That light just disappeared!