In both the first and the current book there are references to something called The Seven Sisters. They are only mentioned briefly in the first book. They appear in some of the opening quotes and only a few times by the characters themselves. Only at the end are the Seven Sisters mentioned as being seven bright lights that appear in the night sky.
In the second book they play a more significant role. You learn that there is a religious connection to them. The residents of Pa'Kevutu believe the Sisters are all just bright stars until circumstances cause them to actually go out and explore one - a heretical act in itself. The idea of the Seven Sisters has always been part of the original (an unrevealed) back story for the entire collection of asteroids called The Milleran Cluster. Although it is not mentioned much in the first text it was always part of the original idea. That idea began over a year ago on the shores of an idyllic lake in Vermont.
Imagine my surprise when I began reading Neal Stephenson's newest book Seveneves. The title of the second chapter is The Seven Sisters. In his book he refers to seven parts of our moon which have just recently and mysteriously broken apart. These seven fragments threaten to break apart and eventually destroy all life on earth.
My sisters are a little less mischievous.