My husband, myself and my eleven year old were stargazing at the planet Jupiter in our southern night sky.

As my husband was positioning his telesccope, I notice an dull looking rectangular object block out the starfield as it moved slowly across the night sky.  This object made no sound, nor did it have any running lights.  
After watching it slowly cross our night sky for a second or two, I asked my husband to look up and see if he sees what I'm seeing.   He acknowledge he did as the object slowly left our field of vision heading southeast.  
It was large (compared to our planes in the sky), and didn't appear high in the atmosphere.