Polarissima Borealis — こぐまの銀河

NGC 3172 is a faint galaxy in Ursa Minor, widely called 'Polarissima Borealis' — the closest NGC-cataloged object to the north celestial pole. It sits less than one degree from Polaris itself, a position that makes it one of the easier galaxies to find for anyone with a go-to mount (because it barely moves in the sky) but also one of the more visually unremarkable: a small, faint elliptical-like galaxy of magnitude 13.6 about 300 million light-years away. Its fame is entirely positional — observers add it to their lists more as a curiosity and a novelty check-off than for its visual interest.

A serious test of dark skies and aperture. At magnitude 13.6 it requires at least a 10-inch telescope to have a realistic chance, 12-inch or more for a confident sighting. The nearby glare of Polaris does not help; offset Polaris to the edge of the field at 200-300x and look for a tiny round fuzzy patch less than half a degree away. Because it is circumpolar from the entire northern hemisphere, it is observable year-round — useful when no other targets are well-placed. Plate-solving a wide-field image in advance is the easiest way to pinpoint it.

Discovered by Lewis Swift on November 19, 1885. The positional nickname 'Polarissima Borealis' was coined by amateur observers in the early 20th century as a matching-pair companion to 'Polarissima Australis' (NGC 2573), the equivalent nearest-the-pole galaxy in the southern hemisphere. The two names have persisted in amateur lore as a 'polar doublet' objective — bagging both requires travel to opposite hemispheres.