Nebulas carry some of the most evocative names in astronomy: the Crab, the Eagle, the Horsehead, the Pillars of Creation. These names arrive through a mix of visual resemblance, historical accident, catalog numbering systems, and occasionally pure whimsy, and the story behind them reveals quite a bit about how astronomy itself has changed over the centuries. The word “nebula” alone has shifted meaning dramatically since it first entered the astronomer’s vocabulary, and some of the names we use today are flat-out misnomers that stuck around because tradition proved stronger than accuracy.
Where the Word Itself Comes From
Nebula is Latin for “mist” or “cloud,” and early astronomers used it to describe anything in the night sky that looked fuzzy rather than point-like. Before telescopes became powerful enough to resolve fine detail, a huge range of objects fell under this umbrella: actual clouds of gas and dust, star clusters too distant to pick apart, and even entire galaxies millions of light-years away. For centuries, “nebula” was less a scientific classification than a confession of ignorance. If it was blurry, it was a nebula.
That broad usage persisted far longer than most people realize. Even after Edwin Hubble demonstrated in the 1920s that spiral nebulae were actually independent galaxies far beyond the Milky Way, astronomers continued calling them “extragalactic nebulae” for decades. The word “galaxy” only became the standard term around 1960, roughly forty years after the discovery that should have retired the old label.1Journal for the History of Astronomy. Nebulae or galaxies? The history of a change in astronomical terminology This kind of terminological drag is a recurring theme in how nebulas get named: once a label takes hold, it sticks.
Why So Many Nebulas Are Named After Animals and Objects
The popular names that most people know, the ones that show up on posters and in documentaries, almost always come from visual resemblance. Someone looks at a photograph or a telescope eyepiece view, sees a shape that reminds them of something familiar, and the name catches on. The Horsehead Nebula genuinely looks like a chess knight silhouetted against a glowing backdrop. The Cat’s Eye Nebula has concentric rings that evoke a feline pupil. The Crab Nebula earned its name in the 1840s when an observer thought its filamentary structure resembled crab legs, though later photographs make it look less crab-like and more like an explosion frozen in time, which is essentially what it is.
These nicknames are informal. They have no official standing with the International Astronomical Union (IAU), the body that governs celestial nomenclature. But they endure because they are memorable and because they serve a real function: they let people talk about specific objects without rattling off a string of numbers. Nobody at a star party says “let’s look at NGC 7293.” They say “let’s find the Helix Nebula.”
Some popular names reference mythology or cultural imagery rather than direct visual similarity. The Orion Nebula sits in the sword of the hunter constellation, so the association is positional rather than shape-based. The Veil Nebula suggests a delicate, draped fabric, which is a fair description of its wispy supernova remnant structure. The Ring Nebula looks like a ring. Sometimes the naming process really is that straightforward.
The Catalog Systems That Give Nebulas Their Official Labels
Underneath every charming nickname is at least one catalog number, and understanding those catalogs explains a lot about how astronomers actually identify and communicate about nebulas.
The oldest widely used catalog is the Messier catalog, compiled by French astronomer Charles Messier starting in the 1770s. Messier was hunting comets, and he kept getting distracted by fuzzy objects that were not comets. So he cataloged them as nuisances to avoid, essentially creating a “do not confuse with a comet” list. The Messier numbers, M1 through M110, now include some of the most famous deep-sky objects in the Northern Hemisphere. M1 is the Crab Nebula. M42 is the Orion Nebula. M57 is the Ring Nebula. The irony is that Messier’s catalog of things he did not care about became one of the most celebrated lists in amateur astronomy.
The New General Catalogue (NGC), published by J.L.E. Dreyer in 1888, is far larger, containing nearly 8,000 objects. Its sequel, the Index Catalogue (IC), adds thousands more. NGC numbers are the workhorse designations that professionals rely on. When you see an object labeled NGC 6543, that is the Cat’s Eye Nebula. NGC 2392 is the Eskimo Nebula (a name that the astronomical community has been moving away from in recent years out of cultural sensitivity). IC 5070 is the Pelican Nebula.
Modern survey telescopes and space missions generate their own catalogs with their own naming conventions. Objects discovered by the Spitzer Space Telescope, the Hubble Space Telescope, or ground-based surveys like the Sloan Digital Sky Survey get alphanumeric designations that follow each survey’s system. These names are practical and machine-readable but entirely unromantic. A newly identified planetary nebula might be cataloged as something like PN G342.0+27.7, where the numbers encode its galactic coordinates. Nobody is writing poetry about that.
Why “Planetary Nebula” Is One of Astronomy’s Worst Misnomers
Planetary nebulae have nothing to do with planets. The name dates to William Herschel in the late 1700s, who noticed that some nebulae appeared as small, round, greenish discs through his telescope, vaguely resembling the planet Uranus (which he had discovered a few years earlier). The name stuck, and astronomers have been explaining the mistake ever since.
A planetary nebula is actually a shell of glowing gas ejected by a dying star, typically a star roughly the mass of our Sun that has exhausted its fuel and shed its outer layers. The exposed core, which becomes a white dwarf, floods the expanding shell with ultraviolet radiation, causing the gas to glow. These objects are temporary by cosmic standards, lasting only tens of thousands of years before the gas disperses and fades. The shapes they produce are strikingly varied. A Hubble Space Telescope study of 119 young planetary nebulae developed a comprehensive morphological classification system to organize this diversity, identifying features such as ansae (handle-like projections caused by jets punching through slower-moving gas), equatorial waists indicating concentrated rings of matter, and point-symmetric structures suggesting the central source is precessing over time.2The Astronomical Journal. Young Planetary Nebulae: Hubble Space Telescope Imaging and a New Morphological Classification System
The popular names for planetary nebulae tend to emphasize their visual appeal: the Butterfly Nebula, the Dumbbell Nebula, the Little Ghost Nebula. These names map onto the morphological variety that classification systems try to formalize, but they do so through poetic impression rather than physical description. A “butterfly” shape in popular parlance corresponds to what an astronomer would call a bipolar structure with an equatorial waist. Both labels describe the same thing; one just sounds better at a dinner party.
Names That Changed or Fell Out of Favor
Nebula names are not set in stone. The shift from “spiral nebulae” to “spiral galaxies” is the most dramatic historical example, but smaller renamings happen regularly. The Eskimo Nebula (NGC 2392) was referred to by that name in astronomical literature for decades, but in 2020 NASA announced it would stop using the term, citing its harmful connotations for Indigenous Arctic peoples. The agency also dropped the name “Siamese Twins Galaxy” around the same time. These objects still carry their catalog numbers, which serve as stable identifiers regardless of which popular name is in or out of fashion.
The IAU itself does not officially assign popular names to nebulae in the way it does for stars (through its Working Group on Star Names) or planetary surface features. This means nebula nicknames live in a gray zone: widely recognized, used in professional papers, printed on merchandise, but not formally sanctioned. The lack of official oversight is partly why so many objects accumulate multiple names. The Omega Nebula is also called the Swan Nebula, the Horseshoe Nebula, and the Lobster Nebula, depending on who you ask and which part of it they are looking at. M17 is the only designation everyone agrees on.
How Modern Discoveries Get Named
The era of large-scale sky surveys and citizen science has changed how nebulae are found and, by extension, how they get labeled. Projects like the Milky Way Project enlisted over 35,000 volunteers to scan images from the Spitzer Space Telescope, identifying bubble-like structures in the interstellar medium. A machine-learning algorithm trained on those citizen identifications proved as capable as expert astronomers at spotting bubbles, though it also revealed that roughly ten to thirty percent of objects in the citizen-generated catalog were non-bubble interlopers.3The Astrophysical Journal Supplement Series. The Milky Way Project: Leveraging Citizen Science and Machine Learning to Detect Interstellar Bubbles Objects found through these pipelines typically receive catalog designations tied to the survey, not poetic nicknames.
Amateur astronomers still occasionally discover new planetary nebulae, and a handful of these carry their discoverers’ names informally. But the sheer volume of objects being cataloged by automated surveys means most new nebulae will never get a popular name. They will exist as entries in a database, interesting to specialists and invisible to the public. The named nebulae, the ones with evocative monikers and gorgeous images, represent a tiny fraction of the total. They are the ones that somebody bothered to look at closely enough to see a shape in.
The Role of Color in How We Perceive and Name Nebulas
The vivid colors in nebula photographs are real in the sense that they represent actual physical emission from atoms and molecules, but they are heavily processed. When astronomers image a nebula, they often use narrow-band filters tuned to specific wavelengths of light: hydrogen-alpha (red), oxygen III (blue-green), sulfur II (deep red). The resulting images are then assigned colors and combined into composites. The choices are partly scientific and partly aesthetic. Narrow-band data of nebular targets can render the various emission-line components in vivid, well-separated colors, but stars in the same image often lose their expected appearance because narrow-band filters do not adequately sample the continuous spectrum of starlight.4Publications of the Astronomical Society of the Pacific. The Aesthetics of Astrophysics: How to Make Appealing Color-composite Images that Convey the Science
This processing matters for naming because the colors strongly influence how people perceive a nebula’s shape and character. The Rosette Nebula looks unmistakably rose-like in images that emphasize hydrogen-alpha emission in warm reds and pinks. Process the same data with a different color palette and the floral resemblance weakens. The Blue Snowball Nebula (NGC 7662) gets its name from its appearance in visual-wavelength observations, where oxygen emission gives it a blue-green hue. Infrared or radio images of the same object would not suggest “snowball” at all. Names are often locked in by the first widely circulated image of an object, which means the color processing choices made by one photographer or one space agency press office can shape how an object is known for decades.
Famous Names and the Objects Behind Them
Some nebula names have become cultural touchstones that extend well beyond astronomy. The Pillars of Creation, a formation inside the Eagle Nebula (M16), became one of the most recognizable astronomical images ever taken when Hubble photographed it in 1995. The name was coined for that specific image release. Before 1995, nobody called those dust columns the Pillars of Creation. The name merged a dramatic visual with a poetic idea, the columns are star-forming regions where new stars are being born inside collapsing pockets of gas, and it resonated far beyond the scientific community.
The Crab Nebula (M1) is arguably the most historically significant nebula in terms of what it taught astronomers. It is the remnant of a supernova recorded by Chinese and Japanese observers in 1054 CE, making it one of the few nebulae with a known birthdate. The connection between the historical record and the modern object was not established until the twentieth century, but it provided one of the key pieces of evidence that supernova remnants are physically real expanding debris fields, not just pretty gas clouds.
The Tarantula Nebula (30 Doradus) in the Large Magellanic Cloud is the largest and most luminous star-forming region in the local group of galaxies. Its name reflects the spidery tendrils of gas visible in wide-field images. If it were as close to Earth as the Orion Nebula, it would cover a significant portion of the sky and cast shadows at night. Its scale makes it a favorite target for space telescopes, and the James Webb Space Telescope produced particularly striking images of its interior star-forming structures shortly after beginning science operations.
Dark Nebulas and Their Inverted Naming Logic
Not all nebulas glow. Dark nebulae are dense clouds of dust that block the light of stars and bright nebulae behind them, appearing as voids or silhouettes against a luminous background. Their names follow the same resemblance logic as emission nebulae but in reverse: instead of seeing a glowing shape, you see a dark shape cut out of a bright field. The Horsehead Nebula is technically a dark nebula, a column of dust silhouetted against the glow of IC 434 behind it. The Coal Sack, visible near the Southern Cross, is a large dark nebula that Aboriginal Australian astronomers incorporated into their sky lore long before European observers cataloged it.
Dark nebulae were systematically cataloged by Edward Emerson Barnard in the early twentieth century, and his Barnard catalog (B numbers) remains the standard reference. The Horsehead is Barnard 33. The Pipe Nebula is a combination of Barnard 59, 65, 66, 67, and 78. These catalog numbers coexist with the popular names, and neither system replaces the other. Professional papers use whichever designation is clearest in context, which usually means the catalog number in a data table and the popular name in the introduction.
When the Same Object Has Multiple Names Across Wavelengths
A single physical structure can earn different names depending on which part of the electromagnetic spectrum you observe it in. The Orion Molecular Cloud is a vast complex of gas and dust that includes the Orion Nebula (visible light), the Kleinmann-Low Nebula (infrared), and various radio-wavelength sources with their own designations. These are not separate objects. They are the same cloud seen through different windows. But because radio astronomy, infrared astronomy, and optical astronomy developed semi-independently through much of the twentieth century, each subfield cataloged what it found using its own system.
This multi-wavelength naming creates occasional confusion even among professionals. A paper discussing a radio source might use a designation unfamiliar to an optical astronomer studying the same region. Cross-matching catalogs, linking entries across wavelengths to confirm they refer to the same physical object, is an ongoing project in modern astronomy. Large databases like SIMBAD exist partly to solve this problem, serving as translators between naming systems. You can enter any of an object’s known names and retrieve all the others, along with its coordinates, physical properties, and bibliography. The messy, layered naming of nebulae is less a flaw in the system than a fossil record of how different branches of astronomy grew up looking at the sky through different instruments.