In order to solve the Astronomical Clock Puzzle you need to first have gotten the two missing plates. One can be found by flooding the Kitchen Garden well after having gotten the bolt cutters, and the second is found in Elisabetta Perosi’s Room.
This is the final picture for the clock. The same picture can be found in Jeremy’s Commonplace Book. Focus on connecting the gold lines off the center piece and that will make it easier to complete. The bottom left corner has more red on it.
Once you have the picture, look at the dials on the clock for the Talisman Numbers. 6 is on the largest, 4 is on the middle. 3 is on the smallest. That means on the Talisman, use 6 in the outer ring, 4 in the middle, and 3 in the inner.
The final Talisman position should look like this, with the numbers on the right being (from top to bottom), 6-4-3.