Ptolemy's Cluster
M7, NGC 6475 · Open cluster in Scorpius
- Magnitude
- 3.3
- Size
- 80′
- Effective surface brightness
- 20.0 mag/arcsec²
- Best months
- May, Jun, Jul
- Declination
- -35°
- Filter
- None (broadband target)
A huge naked-eye cluster in the tail of Scorpius, known since antiquity. Fills a smart-scope field.
Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.
How long with each smart telescope
| Telescope | In frame | Bortle 3 (rural) | Bortle 5 (suburban) | Bortle 7 (urban edge) |
|---|---|---|---|---|
| ZWO Seestar S5010 s subs | 1.9× frame | 5 min30 subs | 5 min30 subs | 5 min30 subs |
| ZWO Seestar S50 Pro10 s subs | Only just | 5 min30 subs | 5 min30 subs | 5 min30 subs |
| ZWO Seestar S3010 s subs | 1.1× frame | 5 min30 subs | 5 min30 subs | 5 min30 subs |
| ZWO Seestar S30 Pro10 s subs | 59% | 5 min30 subs | 5 min30 subs | 5 min30 subs |
| DwarfLab DWARF 315 s subs | 81% | 8 min30 subs | 8 min30 subs | 8 min30 subs |
| DwarfLab DWARF mini15 s subs | 1.1× frame | 8 min30 subs | 8 min30 subs | 8 min30 subs |
| DwarfLab Draco30 s subs | 1.1× frame | 15 min30 subs | 15 min30 subs | 15 min30 subs |
| DwarfLab DWARF II15 s subs | 74% | 8 min30 subs | 8 min30 subs | 11 min46 subs |
| Vaonis Vespera II10 s subs | Only just | 5 min30 subs | 5 min30 subs | 5 min30 subs |
| Vaonis Vespera Pro10 s subs | 82% | 5 min30 subs | 5 min30 subs | 8 min49 subs |
| Vaonis Vespera 310 s subs | Only just | 5 min30 subs | 5 min30 subs | 5 min30 subs |
| Vaonis Vespera Pro 210 s subs | 81% | 5 min30 subs | 5 min30 subs | 8 min47 subs |
| Unistellar eQuinox 24 s subs | 2.3× frame | 2 min30 subs | 2 min30 subs | 3 min43 subs |
| Unistellar Odyssey4 s subs | 2.4× frame | 7 min102 subs | 8 min115 subs | 12 min176 subs |
| Celestron Origin10 s subs | 1.6× frame | 5 min30 subs | 5 min30 subs | 5 min30 subs |
| Celestron Origin Mark II10 s subs | 1.8× frame | 5 min30 subs | 5 min30 subs | 5 min30 subs |
Imaging the open cluster
Open clusters are the easiest targets in the sky. The stars are bright, so the aim is colour and tight stars rather than depth: short subs, no filter, and stop before the bright members saturate. The nominal time here gets you clean star colour; more integration only adds background stars.
Per-telescope pages
- How long to image the Ptolemy's Cluster with the ZWO Seestar S50
- How long to image the Ptolemy's Cluster with the ZWO Seestar S50 Pro
- How long to image the Ptolemy's Cluster with the ZWO Seestar S30
- How long to image the Ptolemy's Cluster with the ZWO Seestar S30 Pro
- How long to image the Ptolemy's Cluster with the DwarfLab DWARF 3
- How long to image the Ptolemy's Cluster with the DwarfLab DWARF mini
- How long to image the Ptolemy's Cluster with the DwarfLab Draco
- How long to image the Ptolemy's Cluster with the DwarfLab DWARF II
- How long to image the Ptolemy's Cluster with the Vaonis Vespera II
- How long to image the Ptolemy's Cluster with the Vaonis Vespera Pro
- How long to image the Ptolemy's Cluster with the Vaonis Vespera 3
- How long to image the Ptolemy's Cluster with the Vaonis Vespera Pro 2
- How long to image the Ptolemy's Cluster with the Unistellar eQuinox 2
- How long to image the Ptolemy's Cluster with the Unistellar Odyssey
- How long to image the Ptolemy's Cluster with the Celestron Origin
- How long to image the Ptolemy's Cluster with the Celestron Origin Mark II