About IC 4642
IC 4642 is an uncommon nebula. It sits in the constellation Ara and shines at apparent magnitude 13.4.
A planetary nebula: the shed outer atmosphere of a dying Sun-like star, lit from within by the naked stellar core left behind.
Uncommon nebula 23 EP
IC 4642
RA 257.9384° · Dec -55.3990° · openngc
Score breakdown
· 3 badgesUncommon 34 pts → Rare
- Planetary nebula (a dying star's shell) +12
- Nebula +8
- Faint fuzzy (mag > 13) +3
Total score 23
11 more points to reach Rare.
Badges
- Nebula · +8
- Planetary nebula (a dying star's shell) · +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 13.4 it is far too faint for the eye: this one belongs to cameras and long exposures, over in Ara.
- Southern sky. It rides the southern half of the sky — an easier target the further south you are.
- Best time of year. It stands highest in the middle of the night around June — 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 Index Catalogue. The IC was the 1895 and 1908 supplement to the NGC — the first catalogue in history to be filled largely with objects found on photographic plates rather than by eye.
Properties
- constellation
- Ara
- dso type
- PN
- mag
- 13.4
- name
- IC 4642
- radial velocity kms
- 44
- redshift
- 0.0001
- size arcmin
- 0.28
How to see it
Look for IC 4642 in the constellation Ara. At apparent magnitude 13.4, it takes a larger telescope or a long-exposure image to capture.
Like any astronomical target, IC 4642 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 IC 4642 is an uncommon nebula
IC 4642 scores 23 points on Spacedle's rarity scale, which places it in the uncommon tier. Another 11 points would lift it into a rarer tier.
That score comes from 3 science badges — Nebula, Planetary nebula (a dying star's shell) 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.