Types of Nebulae, Explained

The word "nebula" just means a cloud of gas and dust in space — but it covers a handful of different things, and the difference is exactly what decides whether it glows red, blue, blocks the light of the stars behind it entirely, or does all three.

Emission nebulae - the ionised cloud

An emission nebula is lit from within. A nearby young, hot star blasts the surrounding hydrogen gas with enough energy to ionise it, causing the gas to glow— mostly a deep red from hydrogen-alpha light. The Orion Nebula (M42) is the best-known example of this type, but here is one of my own shots of the North America Nebula, another prime example. Once Orion is higher within the East Devon skies, I’ll add my own shot here too.

See the North America Nebula in the gallery →

Reflection nebulae - lit by a star within

A reflection nebula doesn't produce any light of its own — it's dust, reflecting the light of a star located nearby, the way a torch beam lights up smoke or fog. Dust scatters blue light more easily than red (which is also why our own sky is blue during the day), so these tend to look blue rather than red.

See the Iris Nebula in the gallery →

Dark nebulae - the cosmic light shields

A dark nebula consists of dust thick enough to block light rather than scatter or emit it — you only ever see it as a silhouette against something bright behind it. The Horsehead Nebula is the classic example: not a glowing horse-shaped cloud, but a dense dust cloud shaped like a horse's head, blocking the glowing emission nebula sitting directly behind it. I’m waiting for the Winter months to shoot this target, so keep an eye on the gallery and my Instagram page.

Planetary nebulae - a dying star's outer layers

Despite the name confusingly, a planetary nebula has nothing to do with planets — 18th-century astronomers thought that the small round glow looked planet-like through a small telescope, like Jupiter or Saturn. It's actually the outer layers of a dying, sun-like star, ejected off into space and lit up by the hot stellar core left behind at the centre.

See the Dumbbell Nebula in the gallery →

Supernova remnants - the aftermath of a stellar explosion

A supernova remnant is what's left after a massive star explodes — the shockwave and expelled gas, still glowing and expanding years, even thousands of years, later. The Crab Nebula (M1) is the remnant of a supernova recorded by astronomers in 1054 AD; the Veil Nebula is the remains of a star that exploded tens of thousands of years ago, its shockwave still visibly expanding across a huge patch of sky. This is one of my personal favourites to photography, due to it’s structure, size and colour range.

See the East Veil Nebula in the gallery →

Next time you're using the sky map on the Calendar page, switch on its deep-sky layer — it'll point out real examples of several of these currently up in the sky over your location.

The different types of nebula above provide a fantastic check list if you’re just starting out in astrophotography. Cross each of them off and more as the skies change through the year. If you’ve captured any of these targets yourself, please send them over on my Instagram page, I’d love to see them!