BEYOND MESSIER
Key Facts: The Major Catalogs
NGC / IC
13,226 Objects (The Universal Standard)
Sharpless (Sh2)
313 Objects (H II Emission Nebulae)
Melotte (Mel)
245 Objects (Star Clusters)
Abell
86 Planetary Nebulae / 4,000+ Galaxy Clusters
Caldwell (C)
109 Objects (Modern Amateur List)
1. The NGC & IC Catalogs (The Gold Standard)
New General Catalogue (NGC): Compiled by John Louis Emil Dreyer in 1888. It was primarily based on the extensive sweeping observations of William Herschel and his sister Caroline, who discovered thousands of objects using their giant speculum-metal reflecting telescopes in England. The NGC contains 7,840 objects spanning the entire sky. Today, if a deep-sky object isn't an "M" (Messier) object, it is almost universally referred to by its NGC number.
Index Catalogues (IC): As astrophotography was born in the late 1800s, cameras began detecting objects too faint for human eyes. Dreyer published two supplements—the Index Catalogues (in 1895 and 1908)—adding 5,386 new objects.
Interesting Fact: Because early astronomers manually recorded coordinates using visual micrometers, the original NGC contained hundreds of errors, typos, and non-existent objects (often just reflections or faint stars mistaken for nebulae). The modern "NGC/IC Project" is an ongoing effort by astronomers to track down the original handwritten notes to correct these historical coordinate errors.
Visit the NGC/IC Project2. Apparent Size & The Field of View Simulator
A common misconception is that deep-sky objects are highly magnified through telescopes because they are incredibly small. In reality, many nebulae and galaxies are physically massive and appear huge in our sky—they are just too faint to see with the naked eye! For example, the California Nebula (NGC 1499) spans nearly 5 times the width of the Full Moon. Select an object below to compare its true apparent size against a standard 5-degree telescope Field of View (FOV).
Field of View (FOV) Simulator
Interact with the controls to load different catalog objects into a standard 5° circular FOV canvas. You can also visualize the framing of common telescopes using a standard APS-C sensor.
The Full Moon
A standard reference. The Moon is roughly 30 arcminutes across. Many deep sky objects are surprisingly much larger.
3. The Sharpless Catalog (Sh2)
Mapping Hydrogen: Published by Stewart Sharpless of the United States Naval Observatory in two editions (1953 and 1959). Sharpless examined images from the Palomar Observatory Sky Survey (POSS) specifically searching for H II regions—massive interstellar clouds of ionized hydrogen gas where new stars are born.
The List: The final "Sh2" catalog contains 313 objects located north of declination −27°. Because these clouds primarily emit light at the very specific red wavelength of 656.3 nm (H-alpha), they are incredibly difficult to see visually but are spectacular targets for modern astrophotographers using narrowband filters.
Famous Targets: Many of the most iconic astrophotography targets belong here, including the Cave Nebula (Sh2-155), the Tulip Nebula (Sh2-101) or The Lobster Claw Nebula (Sh2-157), and the sprawling complex of the Heart and Soul Nebulae.
Browse the Sharpless Catalog
4. Melotte & Abell (Clusters and Ancient Remnants)
The Melotte Catalog
Compiled by British astronomer Philibert Jacques Melotte in 1915. He examined photographic plates spanning the entire sky to systematically identify 245 star clusters. This catalog is beloved by amateur astronomers because it includes many large, loose, beautiful open clusters that Messier missed, such as the Alpha Persei Cluster (Melotte 20) and the cluster at the core of the Heart Nebula (Melotte 15).
The Abell Catalog of PNs
In 1966, George O. Abell published a list of 86 planetary nebulae. Unlike the bright, compact Ring Nebula (M57), Abell's nebulae are ancient, highly expanded, and incredibly faint shells of gas from dying stars. Abell 39 is famous for being an almost mathematically perfect giant bubble of gas.
The Abell Galaxy Clusters
Not to be confused with his planetary nebulae, Abell's most massive contribution to science is the Abell Catalog of Rich Clusters of Galaxies (1958). Containing over 4,000 massive galaxy clusters up to redshift z=0.2, this catalog mapped the large-scale structure of the universe. Famous targets include the Hercules Cluster (Abell 2151), where hundreds of galaxies can be seen interacting in a single frame.
5. The Caldwell Catalog (The Modern Supplement)
Filling the Gaps: The Messier catalog has a major flaw: Charles Messier observed from Paris, meaning he completely missed the Southern Hemisphere. Furthermore, he simply ignored several breathtaking northern objects (like the Double Cluster in Perseus) because they were obviously not comets.
A New List for Amateurs: In December 1995, famous British astronomer Sir Patrick Caldwell-Moore published the Caldwell Catalog. It contains exactly 109 deep-sky objects (to mirror Messier's roughly 110). Unlike the NGC, which is ordered by right ascension, the Caldwell list is ordered by declination, from C1 in the far north to C109 in the deep south.
Highlights: The catalog is packed with true showpieces of the night sky that Messier missed, including the Eta Carinae Nebula (C92), the Omega Centauri globular cluster (C80), and the spectacular Centaurus A galaxy (C77).
Caldwell Catalogue6. Specialized & Modern Catalogs (DWB, LDN, Ou, vdB)
As astrophysics branched into specialized fields and amateur imaging technology caught up with professional observatories, new catalogs emerged. These lists target specific astrophysical phenomena, from pitch-black dust clouds to ultra-faint oxygen emissions discovered only in the 21st century.
The DWB Catalog
Published in 1969 by Dickel, Wendker, and Bieritz, this highly specialized catalog focuses entirely on 193 H-alpha emission nodes within the Cygnus X complex. Astrophotographers often reference this catalog for targets like the iconic Propeller Nebula (DWB 111).
LDN & Barnard
While most catalogs list things that glow, these list things that hide. E.E. Barnard cataloged 349 dark nebulae in 1927. Later, Beverly Lynds published the Lynds' Catalog of Dark Nebulae (LDN) in 1962, mapping thousands of dense, opaque dust clouds blocking background starlight.
The vdB Catalog
Compiled by Sidney van den Bergh in 1966, this catalog contains 158 reflection nebulae. Unlike emission nebulae that create their own light, vdB objects are clouds of interstellar dust shining by reflecting the light of nearby, usually bright blue, stars.
The Ou Catalog
A testament to the modern era, the "Ou" designations belong to Nicolas Outters, a French amateur astrophotographer. Using extremely long exposures and narrowband filters, amateurs are now discovering massive, ultra-faint structures like the Giant Squid Nebula (Ou4), completely missed by historical surveys.
References & Credits
- Дрейер Джон Людвиг Эмиль Русский: Дрейер Джон Людвиг Эмиль, Wikimedia Commons.
- Sir Patrick Moore at the opening of the South Downs Planetarium. Sir Patrick Moore at the opening of the South Downs Planetarium, Wikimedia Commons.