help...mouse effect only working in top half page..

[monster]

recently i added some java script to my blogger...is about the fying star that follow the movement of mouse pointer...

but i dunno why the effect juz working in the top of the page while scrolling down to the page will not seeing the effec...can somebody help me solve this prob? i really dunno wat happen to it...

my blogger:

http://bluemountain82.blogspot.com/

thanks...respect!