Caldwell 73 — Globular Cluster in Columba
NGC 1851
About C73
Description
NGC 1851 is a bright, concentrated globular cluster in Columba, about 39,500 light-years away. It has a dense core and spans about 11 arcminutes, with an integrated magnitude of 7.3 making it one of the brightest globulars in the southern sky.
Observing Tips
Visible as a bright, concentrated glow in a 4-inch telescope. An 8-inch scope begins to resolve the outer stars at 150x+. The dense core remains unresolved in amateur scopes. Best in winter evenings.
History
Discovered by James Dunlop on November 29, 1826 from Australia. It has an unusual double main sequence, suggesting it may have formed from the merger of two clusters or have two distinct stellar populations.
Fun Facts
NGC 1851 has two distinct populations of stars with different chemical compositions, a phenomenon seen in only a few globular clusters. This suggests a complex formation history, possibly involving the merger of two smaller clusters.
Observe
1Properties
Position & Identifiers
2How easy to spot?
| Telescope | Bortle 3 | Bortle 4 | Bortle 5 |
|---|---|---|---|
| 80 mm refractor 80mm refr. | Easy | Easy | Easy |
| 150 mm Newton 150mm Newt. | Easy | Easy | Easy |
| Celestron C8 (203 mm SCT) C8 203mm | Easy | Easy | Easy |
Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs
3Visibility
Set a location in User Settings to see visibility data.
4
Eyepiece View
5
Best Magnification
6Metallicity
[Fe/H] = -1.18 — these stars formed from gas about 15× poorer in iron than the Sun.
7Concentration class
Shapley-Sawyer class III — extremely centrally concentrated core.
Explore
8
Classification Decoder
Discover
9
Light Travel Time Machine
10
Relativistic Travel
Community Photos (1)
Credit: NASA Hubble Space Telescope. License: CC BY 2.0. (Wikimedia Commons)
Skybred Mar 2, 2026
Nearby in the Sky
Other targets within a few degrees — pan your scope a little and keep exploring.
Visibility scores assume a 150 mm Newton at Bortle 4.
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