Large traingular object flying over Perth

5 people saw a UFO advancing directly from the North, travelling South at approximately 9pm Monday 17th June 2014 with full visibility, zero cloud cover, some stars out on a cold and still night. The object resembled a jet fighter – as it was triangular in shape, and no tail. The underside colour of the large craft was a bright burnt orange travelling at a constant speed and flew directly over our home in Girrawheen. The craft took approximately 30 seconds to travel the full length of the sky from North to South as it was noticed by us quite early in the North until it disappeared to the far south as the eye could see. The height of the craft is unknown although it was big and yet there was absolutely no sound detected. We recorded the event on an IPhone, although on playback it looks like a small dot. Commercial aircraft usually fly from south west to north east and East / West on return flight near our home.