Stephenie explains it on her website.
"What does the শিরোনাম refer to? Is it a werewolf reference?
Nope. The term "new moon" refers to the phase of the moon opposite a full moon. It is when the sun is on the opposite side of the moon from us and thus the bright side of the moon is not visible from earth. This is the darkest kind of night. New Moon is the darkest period of Bella's life." link
