I took my dog outside to the backyard one last time before bed, blue light about size of basketball circling my house

I took my dog out to the backyard one last time before bed right at midnight. It was cloudy/foggy/hazy out as it had stormed earlier. There was a blue light about the size of a basketball circling my house maybe just below the treetops (perhaps 80 feet?). It was moving quickly in an oval pattern and seemed "interested" in the roof. I thought it MUST be a reflection or some kind of spotlight, but I watched from my backyard for 8-10 minutes and ruled out any possibility that it could be either of those. It seemed to be the source of the light itself. The light was constant (other than moving). It did not flicker or pulse. It was not a structure. More like energy. I remember thinking it looked like a little blue comet circling the roof. But it kept going and going. So I went inside to see if my husband was awake (he was not) and looked out the front windows to the street to see if there was anything/anyone out there (nothing) and grabbed my cell phone and came back to the backyard. It was still there only lower to the house (maybe 20-30 feet above the roof if that). I tried to take a video, but nothing showed up on the screen, so I just watched a few more minutes. But then I felt like it "noticed" me or something, it came down a few more feet (still above the roof) and began an irregular path (like watching a heartbeat or something--zig-zaggy--up and down but still moving in oval over the roofline). Then I was a little concerned about being out there alone and returned inside the house. My dog never reacted to it and there was no sound coming from it.