Silvery chevron moves across the sky and fades out of sight

It was bedtime for me and my two siblings (ages 9 through 12).  My older sister called out that she saw a UFO.  When we other two got to the window, there was nothing to see, but we stayed in excitement.
 Then it reappeared by fading into view over a few seconds.  It was a solid silvery-gray color, shaped like a rounded crescent moon.  It started slightly obstructed by trees in a generally northern direction and moved slowly and horizontally to the right with the "open" part leading the way.  It was about 15 degrees above the horizon and moved across open sky for an arc of about 45 degrees of sky.  
It then stopped movement, in unobstructed sky, and rotated counterclockwise where the open portion faced upward.  In a matter of seconds, it faded from sight by a decrease in intensity of the light.
Date of incident may be approximate, although the witness does not indicate that fact.  PD