Ptolemy's Cluster
open cluster · Scorpius · 3.3ᵐ
Ptolemy’s Cluster has been known since antiquity — Claudius Ptolemy described it around AD 130 as a nebula following the sting of Scorpius.
Notable facts
About 2.6 times the width of the full Moon in the sky.
In brief
Which constellation is Ptolemy's Cluster in?
Ptolemy's Cluster lies in Scorpius.
Is Ptolemy's Cluster visible to the naked eye?
3.3ᵐ — visible to the naked eye (under dark skies).
When is the best time to observe Ptolemy's Cluster?
Best observed in June.
Data
- RA / Dec (J2000)
- 17h 54m · −34° 49′
- Type
- open cluster
- Constellation
- Scorpius
- How to observe
- 3.3ᵐ — visible to the naked eye (under dark skies)
- Angular size
- 80′
- Designation
- M7 · NGC 6475 · Ptolemy's Cluster
Observing tip
Best in binoculars or a telescope at low power, so the whole cluster fits in the field of view.
Altitude above the horizon by latitude
| Latitude | Maximum altitude | Rise azimuth |
|---|---|---|
| +60° | never rises | — |
| +55° | 0° | 175° |
| +45° | 10° | 144° |
| +30° | 25° | 131° |
| 0° | 55° | 125° |
| −35° | 90° | 134° |
Geometric altitude at upper culmination, atmospheric refraction not included. Positive latitudes are in the northern hemisphere.
Culmination time by month
| Month | Culmination |
|---|---|
| January | 10:08 |
| February | 08:01 |
| March | 06:16 |
| April | 04:22 |
| May | 02:28 |
| June | 00:22 |
| July | 22:18 |
| August | 20:17 |
| September | 18:24 |
| October | 16:35 |
| November | 14:35 |
| December | 12:26 |
Upper culmination in local solar time — no time-zone or daylight-saving correction applied.