If the messier catalog opens with a bang (M1, the Crab supernova remnant in Taurus) and the Caldwell catalog opens with a whisper (NGC 188, an old and dim open cluster in Cepheus), Hidden Treasures opens with a surprise: NGC 189, an 8th-magnitude open cluster in Cassiopeia. The surprise is that indefatigable Caroline Herschel discovered this dim collection of suns in 1783 – a fact that had gone unrecognized for more than two centuries until British astronomical historian Michael Hoskin introduced the world to this fact in the November 2005 Journal for the History of Astronomy.

While reviewing Caroline Herschel's original observing notes, Hoskin scrutinized the following description of an object Caroline discovered on September 27, 1783, shortly after she had discovered the open cluster NGC 225 (Hidden Treasure 2) on the same evening:

Hoskin realized that since NGC 225 precedes Gamma (γ) Cassiopeia, this new object must precede it also. The only deep-sky object in the vicinity of Caroline's description is the 8th-magnitude open cluster NGC 189, which lies nearly 1° southwest of NGC 225. “But it is William's VIII.64 (NGC 381) that is credited to Caroline,” Hoskin says, “even though this cluster follows Gamma Cas.”