Very large translucent triangle

It was a sunny clear morning. The sun was still low in the sky behind me. I think this has a lot to do with what I saw. I was sitting in my car in the parking lot of a local bank waiting for the it to open. I always watch the sky because I am a plane spotter and always have been interested in aviation. I know the usual aircraft that fly around. Plus I live near a major airport so it’s the usual commercial aircraft. I put triangle shape in the description but it started out not triangle. I noticed a mass in the sky moving toward my location, coming from the west. It looked like a flock of birds. That’s what I thought it was at first. The best I could describe it was, it looked like white birds flapping their wings. Like white shimmering shapes. I watched this but I did take my eyes off it because, like I said I thought it was just birds. Again I think the sun angle had a lot to do with this. This is where it gets fuzzy, I don’t recall the shapes getting close! r as I was partially watching but suddenly it was right over my car. I looked up and it was very bright but almost translucent. Then I was so shocked I could make out a triangle shape and a distinct outline of four bright white lights along the back. The rest seemed to be reflecting the sun. I almost get the feeling I wasn’t supposed to see this. I reached for my phone to take a photo or video. Somehow in the couple of seconds it took to reach for my phone I knew it would be gone and I looked back up with phone in hand and it was gone. Disappeared. I really want to know what this was.