You have to call Priority first and then see if your opponent chooses to respond. If they don't use a Counter Trap, then you can go ahead and use your Book of Moon.
Besides, I don't think you have to worry about Priority anyway. I believe his effect is not optional - you have to remove something. Either way, your opponent has the chance to respond with something before you use your Book of Moon. Have fun.
Edit: Someone beat me to it.
Originally Posted by H3LLBOUND
the jury is back. we find the defendant, TheBigBad, guilty of being a complete *******