Answer:
The word "protracted" means lasting longer than expected, or unusually long, so what protracted most clearly means based on the context of the excerpt is how the time period of celestial motion studies must have lasted unusually long.
Bilbo in meeting Gollum in <em>The Hobbit</em>, came in contact with the One Ring, a ring that grants the wearer power of invisibility, and is one of the most powerful rings inside the world of the L.O.T.R.
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