---
title: "NGC 2121"
url: "https://spacecatalog.org/object/ngc-2121"
release: "DR1"
licence: "CC-BY-SA-4.0"
citation: "SpaceCatalog. NGC 2121 [catalogue entry]. Data release DR1 (2026-08-21). https://spacecatalog.org/object/ngc-2121"
---

# NGC 2121

NGC 2121 is a globular [cluster](https://spacecatalog.org/clusters) in the constellation [Mensa](https://spacecatalog.org/constellation/mensa), shining at apparent magnitude 12.37 (V). Other catalogues list it as ESO 057-040 and ESO 57-40. It was discovered in 1836.

## At a glance

- **WHAT IT IS:** Globular cluster
- **HOW BIG ON THE SKY:** 2.7′ — Small enough that the full Moon would cover it several times over.
- **HOW BRIGHT (V):** 12.37 — A small telescope reaches it.
- **WHERE TO LOOK:** [Mensa](https://spacecatalog.org/constellation/mensa) — The patch of sky it sits in, as seen from Earth.

## Properties

| Quantity | Value |
| --- | --- |
| CLASS | Globular cluster |
| APPARENT MAGNITUDE (V) | 12.37 |
| CONSTELLATION | Mensa |
| RIGHT ASCENSION (J2000) | 05h 48m 12.8s |
| DECLINATION (J2000) | −71° 28′ 47.2″ |
| DISCOVERED | 1836 |

## Catalogue data

### HOW BRIGHT IT IS

What the light adds up to, measured through one filter at a time. A magnitude is a brightness on a backwards scale — the smaller the number, the brighter the object.

| Field | Value |
| --- | --- |
| Apparent magnitude (B) | 13.21 |
| Apparent magnitude (V) | 12.37 |

### WHERE IT IS AND HOW IT MOVES

Position, motion across the sky and the size it covers on it. These are measurements of the object as seen from here, so every one of them depends on where here is.

| Field | Value |
| --- | --- |
| Radial velocity | 232 km/s |
| Redshift (z) | 0.000776 |
| Major axis | 2.7′ |
| Minor axis | 2.2′ |
| Position angle | 30° |

### WHEN IT WAS FOUND

Who first saw it, from where, and by what method.

| Field | Value |
| --- | --- |
| Discovered by | John Frederick William Herschel |

### OTHER NAMES AND NUMBERS

The identifiers other catalogues file this object under, for anyone joining this data to theirs.

| Field | Value |
| --- | --- |
| OpenNGC type code | GCl |
| Wikidata item | Q1047015 |

## Also known as

- ESO: ESO 057-040
- ESO: ESO 57-40
- NGC: NGC 2121

## Source

[OpenNGC](https://github.com/mattiaverga/OpenNGC) — CC-BY-SA-4.0

The producer asks: OpenNGC, Mattia Verga (github.com/mattiaverga/OpenNGC). Fields derived from it stay under CC BY-SA 4.0.

How this was made: https://spacecatalog.org/methods#source-openngc

## Cite this page

SpaceCatalog. NGC 2121 \[catalogue entry\]. Data release DR1 (2026-08-21). https://spacecatalog.org/object/ngc-2121

```bibtex
@misc{spacecatalog_ngc-2121,
  author       = {{SpaceCatalog}},
  title        = {{NGC 2121}},
  howpublished = {SpaceCatalog, data release DR1 (2026-08-21)},
  year         = {2026},
  url          = {https://spacecatalog.org/object/ngc-2121},
  note         = {Catalogue entry, data release DR1 (2026-08-21). Values from OpenNGC.}
}
```

OpenNGC — CC-BY-SA-4.0

Acknowledgement the producer asks for: OpenNGC, Mattia Verga (github.com/mattiaverga/OpenNGC). Fields derived from it stay under CC BY-SA 4.0.

The page itself, with its pictures, the sky map and the observing tools: https://spacecatalog.org/object/ngc-2121