Astrology is the seemingly magical study of the stars and other celestial objects for the purpose of predicting the future and has its origins in astronomy. The alignments of the various heavenly phenomena are thought to predict various events, most notably prophecy.
Probably the most notable occurance was when two dragons converged and collided with a third. It is believed that this coincided with Belgrave and Naiya'Nal defeating the Dark Wizard Voth. What is of most interest in this is that the Dark Wizard Voth that the two dragons would fight the third, and then the three of them would fall from the sky. Supposedly this event would cause the stars to lose their familiar positions.
Dragon: When people mention the 'dragons in the sky,' they are referring to comets, not actual dragons.