Caldwell 28 — Open Cluster in Andromeda
NGC 752
About C28
Description
NGC 752 is a large, sparse open cluster in Andromeda, about 1,300 light-years away. At roughly 1.1 billion years old, it is one of the older open clusters and spans a generous 50 arcminutes across the sky.
Observing Tips
Best in binoculars or a wide-field telescope at low power, as the cluster is too large for typical eyepiece fields. About 60 stars from magnitude 8-10 are spread across nearly a full degree. Best in autumn and winter evenings.
History
Possibly observed by Giovanni Battista Hodierna before 1654. Independently found by Caroline Herschel in 1783. One of the benchmark clusters used to calibrate stellar evolution models.
Fun Facts
NGC 752 is old enough that its most massive stars have already evolved off the main sequence, leaving a characteristic red giant branch that helps astronomers test stellar evolution theories.
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
6Where this cluster sits in time
Open clusters span more than four orders of magnitude in age — from newborn OB associations to ancient, metal-rich survivors.
7
Colour-Magnitude Diagram
A cluster's colour-magnitude diagram reveals its age: the bluer the turn-off point where the main sequence bends into red giants, the younger the cluster.
Each point is a Gaia-DR3 member. Colour encodes spectral type; size reflects membership probability.
Explore
8
Classification Decoder
Discover
9
Light Travel Time Machine
10
Relativistic Travel
Community Photos (1)
Credit: Roberto Mura. License: CC BY-SA 3.0. (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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