On the evening of April 23, 2016 at approx. 9pm (do not recall the time) I was on my apartment patio that faces east and I observed a rectangular shaped object for 3-4 seconds before the object went behind trees. I could not locate the object after it went behind the trees. It was travelling west to east and slightly south, similar to jets on landing flight path to Phoenix International Airport (when the planes are travelling west to east). It was moving faster than what a plane on a landing path would move. There was no sound. There were no lights blinking. All I could think was 'what was that?'