The moon is considered a menace. Nowhere near as powerful as the Sun, of course, but still not something worthy of respect. Since astronomy is still not a truly developed science at this point, a lot of this is based on ignorance of astronomical physics. They don't necessarily know that the light from the moon comes from the Sun. To them it's just a foreign god trying to pull worshippers away from the Sun with its meager light.
And yup, Jezzika got it right on! Magic that has to do with water or ice will get you exiled from Solis and killed by the Lumenari because it's the moon that controls tides and things like that. It's like...like worshipping a false idol in Christianity. That kind of thing. All other forms of magic are welcome.
