I was outside, in southern Denver, at around 12:30 in the afternoon looking at contrails while smoking a cigarette, when a movement in the corner of my eye caught my attention. My eyes had to keep focusing on the objects because they appeared to "reflect" (the only word I can think to describe it) the clear blue sky. There were a cluster of objects very high in the sky. My first thought was birds, seagulls specifically, chasing each other. My second thought was military planes dogfighting. They did not appear to be lights, and they were too high to make out a shape. That's when they stopped and hovered in place for approximately 8-10 seconds. The whole time my eyes are straining to focus on them, and I believe because of the angle of the objects in the sky, in relation to me on the ground, I lost sight of all but 6 of them. The 6 "formed up" into two V-shaped formations, one behind the other and extremely quickly left in a northerly direction. The point of the V pointing north. This whole experience lasted approximately 20-30 seconds.(the formation detail... Put a dot on each point of a triangle... there were two formations, 6 total objects.)It's now 2:36pm, and I'm still shaking about what I saw...