Cave Nebula (Caldwell 9)
A glowing cloud in Cepheus lit by HD 217086, a hot young star. A dark lane of dust along one side makes the cave its name comes from.
Emission nebula in Cepheus.
Can you see it from Guyana?
From Georgetown (6.8° N) it climbs to 34° above the northern horizon at its highest; from Lethem (3.4° N), to 31° above the northern horizon. It is highest at midnight on the night of 3 Sep, in the middle of its season. The page works out tonight's rise, highest point and set for both towns in Guyana time (UTC-4), and where the Moon is.
What you'll see
- Your eyes: Not visible to the eye. It lies 9.3° north-west of Caph.
- 10x50 binoculars: Not visible in binoculars.
- A small telescope (80 to 100 mm): Very faint: a dark site, low power and a UHC or OIII filter show its bright edge.
- A camera: Spans about 40% of an APS-C frame at 600 mm (field 2.2° × 1.5°); needs a tracking mount. An H-alpha-sensitive (modified) camera brings out its red glow. The photo above covers about two thirds of its outline.
How big, how bright, how far
- Size on the sky: 50′ × 30′, 1.6 Moons across (the Moon is about 31′ wide).
- Distance: 2,760 light-years. The light reaching your eye left it about 2,760 years ago.
- True size: 40 light-years across its catalogued outline; light crosses it in 40 years.
Apparent size from OpenNGC (Mattia Verga), CC-BY-SA-4.0.
What it is made of
- Type
- Emission nebula
What is in it, not measured:
- Ionised hydrogen: glows red where hot stars light it
- Helium and heavier gases: with traces of oxygen, nitrogen and sulphur
- Dust: in dark lanes
- Young hot stars: that light it
How we know: Distance from the Gaia parallax of HD 217086, the hot star that lights it: Gaia EDR3 parallax via SIMBAD (basic.plx_value, 2020yCat.1350....0G), distance = 1/parallax, retrieved 2026-10-21 (HD 217086: 1.1825 +/- 0.0126 mas). True size: the apparent size times the distance (apparent size: OpenNGC (Mattia Verga, CC BY-SA 4.0), commit 4e2398a2).
More deep-sky objects: Bubble Nebula (NGC 7635) · Pacman Nebula (NGC 281) · Blue Snowball Nebula (NGC 7662) · Little Dumbbell Nebula (M76) · Cat's Eye Nebula (NGC 6543) · Crescent Nebula (NGC 6888)