Polarissima Borealis — Galassia in Orsa Minore
NGC 3172
Su Polarissima Borealis
Descrizione
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.
Consigli per l'osservazione
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.
Storia
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.
Curiosità
Despite its name, NGC 3172 is not the single closest galaxy to the north celestial pole in absolute terms — several much fainter galaxies lie closer, but none have historic NGC designations. As the north celestial pole slowly drifts due to precession, NGC 3172 is gradually moving away from its close-pole position — in about 12,000 years the pole will have moved far enough that it won't be 'polar' anymore, and the Vega region will take over instead.
Osservare
1Proprietà
Posizione e identificatori
2Facilità di osservazione
| Telescopio | Bortle 3 | Bortle 4 | Bortle 5 |
|---|---|---|---|
| Rifrattore 80 mm Rifr. 80mm | M. diff.+ | M. diff. | M. diff. |
| Newton 150 mm Newt. 150mm | Diff. | Diff. | M. diff.+ |
| Celestron C8 (SCT 203 mm) C8 203mm | Diff.+ | Diff. | Diff. |
Bortle 3 = rurale · 4 = periferia · 5 = suburbano
3Visibilità
Imposta una località nelle impostazioni per vedere i dati di visibilità.
4
Vista oculare
Polarissima Borealis · 1.1′×1.0′ · N su, E sinistra
5
Miglior Ingrandimento
Esplorare
6
Brillanza superficiale
7
Decodificatore di morfologia
8
Inclinazione e forma reale
9
Spostamento verso il rosso
10
Comparatore di dimensioni
Scoprire
11
Macchina del tempo della luce
12
Viaggio Relativistico
Vicini nel cielo
Altri bersagli a pochi gradi — sposta un po’ il telescopio e continua a esplorare.
I punteggi di visibilità assumono un Newton da 150 mm con Bortle 4.
Esplora Nightbase
Conoscenze, strumenti e storie correlate — senza pianificare osservazioni.