Quite early on in the game, the Astrologer will be mentioned a few times. Especially when it comes to the Portal on Witch Hill which you are told to activate and go through.
The Astrologer can be found at the Lighthouse, and only on certain days. He will only appear when the symbol in the top left is set to the blue crescent moon.
Whilst I havn’t progressed with his quest line a lot yet, I know his location and exactly where to find it. It made sense to share it below.
When you do meet with the Astrologer, he will request a skull which you can collect whilst conducting an autopsy. Below, you can find the location of the Astrologer. Check out some more guides for Graveyard Keeper.
Astrologer Location
As I mentioned earlier, the Astrologer can be found at the Lighthouse. Below is a map of the game world, showing the lighthouse to the east of the Village.

If you go through the village, follow the path East past the tavern, then taking a slight south turn and finally, East again towards the lighthouse. You will know you’re approaching the lighthouse as you go across a path surrounded by trees.

This is the general area, the screenshot above shows the lighthouse. The astrologer can be found near the telescope. As I said before, he will only be there when the symbol in the top left is set to the blue crescent moon.