About NGC 7139
NGC 7139 is a rare nebula. It sits in the constellation Cep and shines at apparent magnitude 13.3.
A planetary nebula: the shed outer atmosphere of a dying Sun-like star, lit from within by the naked stellar core left behind.
Rare nebula 49 EP
NGC 7139
RA 326.5358° · Dec 63.7919° · openngc
Score breakdown
· 6 badgesRare 50 pts → Epic
- Planetary nebula (a dying star's shell) +12
- Its dying star is still visible +12
- Coming towards us +10
- Nebula +8
- Never sets (northern circumpolar) +4
- Faint fuzzy (mag > 13) +3
Total score 49
1 more point to reach Epic.
Badges
- Nebula · +8
- Planetary nebula (a dying star's shell) · +12
- Never sets (northern circumpolar) · +4
- Coming towards us · +10
- Its dying star is still visible · +12
- Faint fuzzy (mag > 13) · +3
Trivia
What it actually is
- What it actually is. A planetary nebula: the shed outer atmosphere of a dying Sun-like star, lit from within by the naked stellar core left behind.
Find it in the sky
- How to spot it. At magnitude 13.3 it is far too faint for the eye: this one belongs to cameras and long exposures, over in Cepheus.
- Never sets. So far north that from Britain, Canada or northern Europe it never dips below the horizon — it is up every clear night of the year.
- Best time of year. It stands highest in the middle of the night around August — that's when to go looking.
Its true colour
- Its true colour. Its teal-green comes from doubly-ionised oxygen at 501 nanometres, and its red from hydrogen at 656 — colours no ordinary object on Earth produces.
What's in a name
- A misleading name. 'Planetary nebula' is a 240-year-old mistake. William Herschel coined it in the 1780s because these round greenish discs resembled the planet Uranus he had just discovered. There are no planets involved whatsoever.
How we came to know it
- The New General Catalogue. Its NGC number comes from J. L. E. Dreyer's 1888 catalogue, itself built on decades of sky sweeps by William Herschel and his sister Caroline.
Properties
- central star mag
- 18.72
- constellation
- Cep
- dso type
- PN
- mag
- 13.3
- name
- NGC 7139
- radial velocity kms
- -54
- size arcmin
- 1.28
How to see it
Look for NGC 7139 in the constellation Cep. At apparent magnitude 13.3, it takes a larger telescope or a long-exposure image to capture.
Like any astronomical target, NGC 7139 is best seen from a dark site away from city lights, and when it is above the horizon depends on your latitude and the time of year. The visibility panel above works out tonight's viewing window for your saved location.
Why NGC 7139 is a rare nebula
NGC 7139 scores 49 points on Spacedle's rarity scale, which places it in the rare tier. Another 1 point would lift it into a rarer tier.
That score comes from 6 science badges — Nebula, Planetary nebula (a dying star's shell), Never sets (northern circumpolar), Coming towards us, Its dying star is still visible and Faint fuzzy (mag > 13) — each earned for a real, measurable property of the object. Rarity on Spacedle is never random: the more remarkable an object's astrophysics, the more badges it collects, the higher it scores, and the rarer it ranks.