The magical art of Astromancy, or Astrotheurgy as the use of the art is known as, is the arcane manipulation of magic to achieve effects based around the sun, moon, stars and other stellar phenomenon. It is probably the rarest of magic even though it has been practiced in some way, shape or form by almost every culture.
As long as people have been able to see, the skies have captivated them, the stars even more so. Entire cultures have developed over the worship of suns or moons, their mystery always drawing interest and curiosity. Primitive Astromantic spells were generally used for divination though as time went on more and more spells began to be developed that utilized other concepts.
In the Second Age, an incredible explosion of exploration occured in all directions and with increasing developments in optical aids such as telescopes the stars were just as viable a venue to explore as anything else. It was also during this time that the first Astromancers left their planets to actually explore the stars, bringing back more information with each return trip.
Astromancers are definitely not as common as other wizards but their magics are no less powerful or impressive. They have a unique reputation as the bane of Therianthropes such as werewolves and wererats, as the Astromancer's capability to manipulate lunar properties allows them to effect these creatures in ways normally others can't. Vampires also loathe Astromancers, as they can conjure the sun's light in the most isolated and secluded of places, literally bringing one of the vampire's weaknesses directly to them. Being able to see portents and read the stars, it's not uncommon for an Astromancer to act as an impromptu fortune-teller should the need arise.