Truth Behind the Scenes has presented UFOs in video going behind the moon, or casting a shadow directy upon it. 

Their blooggers indicate that "since we have a distinct point of reference, and the moon it self can be used to calculate size"  They estimate that "these objects are between 60 and 80 miles in diameter. The one going behind the moon may be larger. 90 – 110."

internet site reference: http://thetruthbehindthescenes.wordpress.com