When Sam is allowed to enter the Citadel's library in Oldtown he comes across this giant spinning contraption hanging from the ceiling. Redditor Samurio noticed it looked similar to the object seen in the show's opening credits.

According to Angus Wall, Creative Director at Elastic, the company that created the opening credits map intro, it's called an astrolabe. Historically, they've been used by explorers and astronomers alike to record time and measure the position of the sun, stars, and planets.

Even though we know what it's called, we have no idea what the point of this astrolabe could be at the Citadel. Does it predict the changing seasons? Could it be a mere decoration (probably not)? Hopefully we'll find out more in season seven.