M70
Globular Cluster in Sagittarius
About
NGC 6681, a globular cluster in southern Sagittarius about 29,400 light-years away. It has undergone core collapse, which leaves its stars heavily concentrated toward the centre. Comet Hale-Bopp was discovered near it in 1995.
Imaging tips
- About 8′ across, so 3,030–5,050 mm on APS-C; too small for full frame, so use a long focal length and a fine pixel scale.
- One remote-telescope image used a 20-inch f/6.8 reflector and 5 h 40 min in total: 2 h 10 min of luminance plus 3 h 30 min of colour.
- Globular clusters need broadband filters; narrowband adds nothing for a cluster of stars.
- It stays below 8° altitude from 50°N and reaches 23° from 35°N, so low altitude is the main obstacle for northern imagers.
- Best around June and July.
Facts
- Size
- 8′
- Magnitude
- 7.8
- Coordinates
- RA 18h 43.2m, Dec −32° 18′
- Framing, APS-C
- 3030–5050 mm
- Framing, full frame
- longer than 4000 mm
- Best months
- Jun, Jul
- Peak altitude
- 8° from 50°N, 23° from 35°N