It was hard to describe, but it looked to be expanding at the front like a balloon, then using that air to propel itself along. It was roughly 100 meters above me and I watched it for 10 minutes. After that it was out of sight. This was during a clear night sky in Australia. I am very familiar with aircraft as I live relatively close to Jandakot airport and we see/hear them all the time. It was certainly not a machine of any kind. I yelled out to my Mother-in-Law who was staying at the time to come out and look. She also saw it. I filmed it on my smartphone,