In this world people don't worship specific gods but the Heavens themselves. When the story takes place there are only six Astronomers, and they aren't just scientists that observe the sky. They have the energy of the stars inside them which gives them a magic link to them. As a result they have been single-handedly responsible for every astronomical discovery and advanced their societies' knowledge considerably.

They also possess great wisdom beyond astronomy, since the stars have been around for all history, and they carry that with them. Because of this they are leaders and rulers of their countries/cities.

Their power also grants them greater energy, both in the immediate short term, but also in the longterm as they live twice as long as normal people. They can also transfer that energy to an extent (like making a metal sword glow red-hot.)

As mentioned above there are only six of them, and their power is passed on when they die to someone who is in physical contact with them (it would be lost otherwise.) It is all prearranged who will be next in line and it is passed on in a formal ceremony.

Now I am stuck on how the original Astronomers got their power in the first place. One idea is that it involves a rare celestial event, like a supernova appearing in the sky. These occur about once a century or so and that's how they've slowly increased their numbers over time to their current state. But I'm not sure what they actually do during that window to become an Astronomer. Any ideas?