White rectangular object, climbing steeply into the sky.We were sitting outside enjoying the late afternoon/early evening. I happened to look up in the sky and saw a white rectangular form climbing steeply into the sky. At one point, the sun reflected brightly off of it (for several seconds). It climbed very quickly-to the south/southwest and disappeared when passing over, then beyond a tall cumulus cloud in the distance. By this time, it merely a white speck in the sky.It was completely silent. It didn't have wings. It was in a position where we would have heard the sound of it, climbing into the sky. I've never seen anything like this in entire lifetime+.((ADDENDUM FROM WITNESS))Sorry about the date. It was early evening Wed. June 28., ((END ADDENDUM))