Triangle shaped UFO passing over my apartment.

I am not sure if it was a balloon or a UFO, but I first noticed the object in the sky far away and I thought it was a bird. As the object got closer, it look like it was spinning in circles and illuminating in light and then got darker and then brighter again. The object was quiet and moving maybe 10 to 15 mph. It was shaped like a triangle and then stopped spinning in circles when it was approaching over my apartment and continued moving straight. There was no wind and the weather was calm. I believe it did not have the characteristics of a balloon because there was no design on it or a string attached to the object. I have never seen anything like the object I saw. There were no blinking lights too. When I first noticed the object I was stunned and then realized I should try to record the UFO on my phone before it went away.