A square light in the sky, which disappeared, reappeared, and disappeared.

I was watching the demolition derby at the Union Fair, when I noticed a light in the sky out of the corner of my eye. I looked up and saw an apparently silent square (though it was more of what Google tells me is a squircle) of bright white light moving slowly across the sky. I glanced back to the derby, and then looked up again. The object was gone, but then reappeared. I looked back at the derby again, and when I checked again, the object was gone. I looked back, observing the sky but it was gone. Throughout the remainder of the demolition derby, I'd look back up, but I never saw it again.