H-NGC6633
Open Cluster in Ophiuchus
About
A bright open cluster in Ophiuchus, about 1,040 light-years away and around 550 million years old. It spans about 27′, close to the width of the full Moon, and counts 38 known stars. It goes by Captain Hook Cluster and, paired with IC 4756, Tweedledum.
Imaging tips
- At 900–1500 mm on APS-C (1380–2290 mm full frame) the cluster fills a third to half of the frame.
- IC 4756 lies about 3° away. One imager framed both with a 300 mm lens on a 5.2° × 3.8° field, 25 minutes in total.
- Another imager used a 135 mm lens with a light-pollution filter, 11 × 6 minutes with a one-shot colour camera.
- One LRGB example at about 1,200 mm gathered roughly 2 hours in total.
- Best around June and July; it peaks near 47° altitude from 50°N.
Facts
- Size
- 27′
- Magnitude
- 4.6
- Coordinates
- RA 18h 27.4m, Dec +6° 37′
- Framing, APS-C
- 900–1500 mm
- Framing, full frame
- 1380–2290 mm
- Best months
- Jun, Jul
- Peak altitude
- 47° from 50°N, 62° from 35°N