Nestled in the rich, starry backdrops of northwestern Cassiopeia lies a delightful celestial pairing often overlooked by observers rushing toward brighter showpieces. Open cluster NGC 7788 sits just 17 arcminutes northwest of its larger, slightly brighter sibling, NGC 7790, forming a cozy double-cluster view in wide-field eyepieces. John Herschel first logged this little jewel in 1829, describing it as a condensed grouping anchored by a single 10th-magnitude star, surrounded by a swarm of much fainter companions. Spanning roughly 4 arcminutes across, NGC 7788 brings to mind a tiny, sparkling brooch pinned against the Milky Way's velvet tapestry.
Through a small refractor at modest magnification, the cluster presents an intriguing visual puzzle. A 4-inch scope at 50× easily catches the lead 10th-magnitude star shining bright on the cluster’s edge, while its faint stellar entourage melts into a soft, glowing, triangular patch of unresolved light. Increasing the power to around 120× transforms that subtle haze, coaxing a dozen or so pinprick stars around 12th and 13th magnitude out of the background glow. The cluster’s compact core (the cluster having been classified as Trumpler type I2p) gives it a surprisingly tight, almost globular-like neatness, offering a pleasing contrast to the looser, more scattered arrangement of nearby NGC 7790.
Astrophysically, NGC 7788 is a youthful cosmic nursery, estimated to be just 20 to 40 million years old—roughly half the age of its neighboring companion. While NGC 7790 gains much of the professional spotlight for harboring three rare Cepheid variable stars, NGC 7788 holds its own charm for visual observers who enjoy binary deep-sky targets. Star-hop about 3 degrees northwest of 1st-magnitude Caph (Beta Cassiopeiae) to center the pair. Framing both open clusters together in the same field of view yields a wonderful study in stellar evolution and spatial perspective, serving as a gentle reminder that some of the sky's best treasures come in pairs.