M75
Globular Cluster in Sagittarius
About
NGC 6864, a globular cluster in Sagittarius about 67,500 light-years away, found by Pierre Méchain in 1780. Its stars are packed toward the centre more tightly than in most globulars (Shapley-Sawyer class I), and it holds 38 RR Lyrae variable stars.
Imaging tips
- About 6′ across, so it is too small to frame: use a long focal length and a fine pixel scale.
- One imager treated it as a plain broadband target: an hour of 30-second subs with a one-shot colour camera at f/2 was enough, with no nebulosity or dust around it to process.
- The same write-up warns the cluster looks smaller in the frame than its size suggests, so expect to crop and plan enough focal length.
- Low from northern sites: it stays below 18° altitude from 50°N. Best around July and August.
Facts
- Size
- 6′
- Magnitude
- 8.5
- Coordinates
- RA 20h 6.1m, Dec −21° 55′
- Framing, APS-C
- longer than 4000 mm
- Framing, full frame
- longer than 4000 mm
- Best months
- Jul, Aug
- Peak altitude
- 18° from 50°N, 33° from 35°N