Caroline's Rose — カシオペヤの散開星団

NGC 7789 is a rich, densely populated open cluster in Cassiopeia, about 7,600 light-years away, popularly known as Caroline's Rose or the White Rose Cluster for its intricate star-strewn structure resembling the layered petals of a rose. The cluster contains over 1,000 stars and is one of the oldest open clusters still visibly recognizable in the Milky Way — its age is estimated at 1.6 billion years. Its population includes both blue main-sequence stars and a well-populated red-giant branch, making it one of the best 'snapshots' of stellar evolution a visual observer can inspect in a single field.

A showpiece for 4-inch telescopes and larger, where it reveals its rose-like density. In binoculars it appears as a small soft glow, resolved only into a handful of its brightest members. A 4-inch at 80-100x shows the full layered structure: clumps of stars separated by subtly darker lanes, arranged in graceful curves that inspire the 'petal' imagery. An 8-inch at moderate magnification is glorious — the cluster holds up to scrutiny and grows more intricate the more you look. Use averted vision to draw out the faintest members. Best observed August through February when Cassiopeia is circumpolar and high.

Discovered by Caroline Herschel in 1783 during one of her systematic sweeps of the Milky Way with a small sweeper telescope of her own design. Caroline was the first professional woman astronomer and catalogued 14 new deep-sky objects; this was one of her most beautiful. Her brother William Herschel later included it in his General Catalogue, and Dreyer gave it the NGC 7789 designation. The 'Caroline's Rose' nickname was bestowed by modern amateur astronomers in tribute to her, and it has become the cluster's most widely used informal name.