Sighted silver disk in motion on a cloudless, sunny day.

I was walking down the street, and noticed the disk in the sky above the horizon by perhaps 30 degrees.  The direction was northwest of my location, in northwest Houston.  It was fairly far away, in my estimation around 2 miles.  The object may have been cylindrical in shape, or disk-shaped but on edge.  I believe it to be the latter.  I would estimate its diameter at roughly 200'.  It was gray in color, or maybe a matte silver like brushed steel.  The object was moving northeast (?) at about 400 ft/s, not very fast.  After observing the object in flight for around 10 seconds, I found that I could no longer locate it. I am a college student, 19.  At the time of this event, I was 13, but I never thought to report it until now, despite my interest in UFOs.  My memory may be sketchy concerning some details, but my recollection of the overall event is accurate.