Sh2-170 — Little Rosette
HII Region in Cassiopeia
About
A faint ring of glowing hydrogen in Cassiopeia, on the Perseus Arm at about 7,500 light-years. It is named for the far larger Rosette Nebula. It holds the cluster Stock 18 and lies close to NGC 7822 in the sky, though the two are unrelated.
Imaging tips
- Sources give about 56′ by 50′, wider than a typical 44′ frame, so plan a mosaic or a wide lens.
- Ionised hydrogen dominates, so narrowband suits it. One imager took 38 Hα, 29 OIII and 17 SII frames of 300 s each, about 7 hours in all.
- In that run the strong Hα signal was visible while shooting, and the OIII and SII data came out noisier and needed heavy noise reduction.
- The same imager wanted at least double the time: faint dust in the field looked smeared after about 7 hours.
- Best in September and October; it peaks near 75° altitude from 50°N.
Facts
- Size
- 20′
- Magnitude
- —
- Coordinates
- RA 0h 1.7m, Dec +64° 38′
- Framing, APS-C
- 1210–2020 mm
- Framing, full frame
- 1860–3090 mm
- Best months
- Sep, Oct
- Peak altitude
- 75° from 50°N, 60° from 35°N