Fan Casting The Hidden Celestials

These books are about a group of eight girls with powerful elemental magic, which allows them to merge into a goddess-like being of creation called Caelesti. Their power comes from planetary core pieces (huge energy reserves) that they unknowingly absorbed as babies. Seven of the girls go to attend a magical academy that deals with elemental and Shifter magic (shape-shifiting). However, events soon get out of hand and the girls discover that there is a doomsday prophecy written about them. Not only that, but a powerful time god inhabiting the body of their headmistress' grandfather, wants to see the universe destroyed and remade to his liking. And he has found them... The girls and their friends have adventures through snowy mountains, time, the deep ocean, space and everywhere you could possibly imagine, all to fulfill and avoid the prophecy as much as they can. But destiny has a way of catching up with you... (Told mainly from the perspective of the main character, Alexa Uiscena - a water elemental - as well as a few other characters).