M17 — Omega Nebula
Emission Nebula in Sagittarius
About
The Omega Nebula (NGC 6618) in Sagittarius, a glowing hydrogen cloud about 5,000–6,000 light-years away and roughly 15 light-years across. Few star-forming regions in the Milky Way are as bright or as massive.
Imaging tips
- At 400–670 mm on APS-C the nebula fits comfortably, with M18 about 56′ away: nearby, in a wider field rather than the same frame.
- Narrowband suits this emission nebula: one imager used a dual-band H/O filter with 10-minute subs, and another used a light-pollution-cutting narrowband filter from a backyard.
- Depth is the cost: 2.5 hours of 10-minute subs was a modest backyard result, while a two-panel mosaic reached 50 hours per panel to bring out faint OIII structure.
- One imager notes that OIII regions get swamped by hydrogen red in colour data, so a slight boost to OIII balances the palette.
- Surface brightness is 23.5 mag/arcsec², faint for its size. Best around June and July, below 24° altitude from 50°N.
Facts
- Size
- 60′ × 60′
- Magnitude
- 6.0
- Coordinates
- RA 18h 20.8m, Dec −16° 11′
- Framing, APS-C
- 400–670 mm
- Framing, full frame
- 620–1030 mm
- Best months
- Jun, Jul
- Peak altitude
- 24° from 50°N, 39° from 35°N