NGC 6818 — Planetary Nebula in Sagittarius
About NGC 6818
Description
NGC 6818, the Little Gem Nebula, is a small bright planetary nebula in northern Sagittarius, about 6,000 light-years away. Its compact disc — only about 22 arcseconds across — has a strong blue-green tint and a high enough surface brightness to be obvious in even modest telescopes. Hubble imaging revealed a beautiful double-shell structure with a bright inner ring and a fainter, almost spherical outer envelope, marked by faint radial filaments threading from the central star outward. NGC 6818 sits less than a degree north of the much larger and fainter dwarf galaxy NGC 6822 — a popular telescopic pairing.
Observing Tips
A 4-inch at 200x shows a small, bright disc with a clear blue-green tint. An 8-inch at 300x resolves the disc cleanly and brings out the slightly ring-like structure when seeing is steady. NGC 6818 takes magnification very well; experienced observers push to 400x and beyond on good nights. After observing the Little Gem, sweep south just under a degree to find Barnard's Galaxy NGC 6822 — a stark contrast between high and low surface brightness. Best observed June through September.
History
Discovered by William Herschel on 8 August 1787. The 'Little Gem' nickname is a 19th-century coinage that captures the nebula's bright, jewel-like appearance at the eyepiece.
Fun Facts
NGC 6818 is one of the very few planetary nebulae that can be confidently observed in the same field as a galaxy of comparable apparent brightness — Barnard's Galaxy — though the nebula's compactness makes it visually far more striking. The two together provide a memorable demonstration of how surface brightness rather than total magnitude determines what is easy to see at the eyepiece.
Observe
1Properties
Position & Identifiers
2How easy to spot?
| Telescope | Bortle 3 | Bortle 4 | Bortle 5 |
|---|---|---|---|
| 80 mm refractor 80mm refr. | Hard | V. hard+ | V. hard |
| 150 mm Newton 150mm Newt. | Hard+ | Hard | Hard |
| Celestron C8 (203 mm SCT) C8 203mm | Hard+ | Hard+ | Hard |
Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs
With O-III filter
| Telescope | Bortle 3 | Bortle 4 | Bortle 5 |
|---|---|---|---|
| 80 mm refractor 80mm refr. | Hard+ | Hard+ | Hard |
| 150 mm Newton 150mm Newt. | Medium | Medium | Medium |
| Celestron C8 (203 mm SCT) C8 203mm | Medium | Medium | Medium |
3Visibility
Set a location in User Settings to see visibility data.
4
Filter Response Guide
5
Eyepiece View
6
Best Magnification
Explore
7
Central Star
8
Surface Brightness
Nearby in the Sky
Other targets within a few degrees — pan your scope a little and keep exploring.
Visibility scores assume a 150 mm Newton at Bortle 4.
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