About NGC 581
NGC 581 is a rare cluster. It sits in the constellation Cas and shines at apparent magnitude 7.4.
An open cluster: a few hundred stars born together out of one collapsing cloud, still drifting along in loose formation.
Rare cluster 42 EP
NGC 581
RA 23.3409° · Dec 60.6580° · openngc
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Score breakdown
· 6 badgesRare 50 pts → Epic
- Messier object +12
- Coming towards us +10
- Star cluster +7
- Bright deep-sky object +6
- Never sets (northern circumpolar) +4
- Open cluster +3
Total score 42
8 more points to reach Epic.
Badges
- Star cluster · +7
- Messier object · +12
- Bright deep-sky object · +6
- Open cluster · +3
- Never sets (northern circumpolar) · +4
- Coming towards us · +10
Trivia
Hard to believe
- Messier object. One of the 110 showpieces of the Messier list — catalogued as M103.
What it actually is
- What it actually is. An open cluster: a few hundred stars born together out of one collapsing cloud, still drifting along in loose formation.
Sense of scale
- Sense of scale. Gravity is not strong enough to hold it. Within a few hundred million years these siblings will be scattered right around the galaxy.
Find it in the sky
- How to spot it. At magnitude 7.4 it is just past naked-eye reach — ordinary binoculars will pull it in, over in Cassiopeia.
- 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 October — that's when to go looking.
Its true colour
- Its true colour. Open clusters look blue-white because they are young — their hottest, bluest stars have not had time to die yet.
How we came to know it
- Messier's anti-list. Charles Messier was a comet hunter, and he compiled his famous catalogue in the 1770s and 80s purely as a list of fuzzy things that are NOT comets. History remembers the distractions and forgets the comets.
Properties
- constellation
- Cas
- dso type
- OCl
- mag
- 7.4
- messier
- yes
- messier number
- 103
- name
- NGC 581
- radial velocity kms
- -46
- size arcmin
- 4.5
Nearby objects
How to see it
Look for NGC 581 in the constellation Cas. At apparent magnitude 7.4, it is an easy target for binoculars.
Like any astronomical target, NGC 581 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 581 is a rare cluster
NGC 581 scores 42 points on Spacedle's rarity scale, which places it in the rare tier. Another 8 points would lift it into a rarer tier.
That score comes from 6 science badges — Star cluster, Messier object, Bright deep-sky object, Open cluster, Never sets (northern circumpolar) and Coming towards us — 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.