Each catalog was made for a different purpose, so the same objects were numbered again and again
An astronomical catalog is a numbered list of objects with their positions. Each one below set out to list a different kind of object, or the whole sky down to a new limit, and the bright showpieces landed in nearly all of them.
- Star names, from antiquity to 1801: some clusters were first listed as stars. Omega Centauri and 47 Tucanae carry star designations, from Johann Bayer in 1603 and Johann Bode in 1801, given before telescopes showed them to be globular clusters.
- Messier, 1774 to 1781: Charles Messier listed fuzzy objects that a comet hunter might mistake for a comet. 110 objects today.
- Herschel, 1786 to 1802: William and Caroline Herschel swept the northern sky with large reflectors and found about 2,500 nebulae and clusters.
- NGC, 1888, and IC, 1895 and 1908: J. L. E. Dreyer's New General Catalogue merged the Herschels' lists and others into 7,840 entries; the two Index Catalogues added 5,386 more, many found by photography.
- Cluster and nebula catalogs, 1915 to 1960: Melotte and Collinder (open clusters), Barnard and Lynds (dark nebulae), Sharpless, Gum and RCW (glowing hydrogen clouds).
- Galaxy catalogs, 1966 to 1973: Arp's Atlas of Peculiar Galaxies and the Uppsala General Catalogue (UGC) of northern galaxies.
- Star cluster catalogs, 2013: the Milky Way Star Clusters catalog (MWSC), which gave a new number to every known cluster in the galaxy, including the Messier clusters.
- Observing lists, 1976 and 1995: the Herschel 400, picked from the Herschels' discoveries for 6-inch telescopes, and the Caldwell list, Patrick Moore's 109 bright objects that Messier missed.
106 of the 110 Messier objects are also NGC objects
Counted from this site's catalog datasets:
| Catalog | Entries | Also listed as |
|---|---|---|
| Messier | 110 | 106 NGC; 2 IC (M24 and M25); M40 is the double star Winnecke 4; M45, the Pleiades, is Melotte 22 |
| Caldwell | 109 | 99 NGC; 7 IC; the Cave Nebula is Sh2-155, the Hyades are Melotte 25 and Collinder 50, and the Coalsack has no catalog number |
| Herschel 400 | 400 | All 400 NGC; 44 also Caldwell; 17 also Messier, including M82, M104 and M51's companion NGC 5195 |
| NGC | 8,373 | 274 entries repeat another NGC object; 212 have a common name |
| IC | 5,586 | 297 entries cross-reference an NGC object; 377 are flagged as duplicates |
| Arp | 338 | 189 include at least one NGC galaxy |
The NGC and IC counts here include the entries in this site's datasets, which list some multiple and duplicate objects separately.
The Omega Nebula carries nine names
Names and catalog numbers for famous objects, as listed in this site's datasets:
| Object | Names and catalog numbers |
|---|---|
| Omega Nebula | Omega Nebula, Swan Nebula, Checkmark Nebula, Lobster Nebula, Horseshoe Nebula, M17, NGC 6618, LBN 60, MWSC 2896 |
| Pleiades | Pleiades, Seven Sisters, Subaru, M45, Mel 22, Cr 42, MWSC 0305 |
| Little Dumbbell Nebula | Little Dumbbell Nebula, Barbell Nebula, Cork Nebula, Butterfly Nebula, M76, NGC 650, PN G130.9-10.5 |
| Eagle Nebula | Eagle Nebula, Star Queen Nebula, M16, NGC 6611, LBN 67, MWSC 2886; the nebula itself is also IC 4703 |
| Orion Nebula | Orion Nebula, Great Orion Nebula, M42, NGC 1976, LBN 974, MWSC 0582 |
| Crab Nebula | Crab Nebula, Taurus A, M1, NGC 1952, LBN 833 |
| Whirlpool Galaxy | Whirlpool Galaxy, Question Mark Galaxy, M51, NGC 5194, Arp 85, UGC 08493 |
| Andromeda Galaxy | Andromeda Galaxy, Great Andromeda Nebula, M31, NGC 224, UGC 00454 |
| Carina Nebula | C92, Carina Nebula, Eta Carinae Nebula, Great Nebula in Carina, NGC 3372 |
| Double Cluster | C14, Double Cluster, h and Chi Persei, NGC 869, NGC 884 |
| Hyades | C41, Hyades, Mel 25, Cr 50 |
| Horsehead Nebula | Barnard 33, part of LDN 1630, seen against the glow of IC 434 |
Catalog abbreviations: NGC and IC, New General Catalogue and Index Catalogue; LBN and LDN, Lynds' catalogs of bright and dark nebulae; MWSC, Milky Way Star Clusters; Mel and Cr, Melotte and Collinder; UGC, Uppsala General Catalogue; Arp, Atlas of Peculiar Galaxies; PN G, the Strasbourg-ESO catalog of planetary nebulae, numbered by galactic position.
One common name can belong to two different objects
Common names are informal, so they repeat. Catalog numbers do not.
- Pinwheel: the Pinwheel Galaxy is M101, but M33 is also the Triangulum Pinwheel, M99 is the Coma Pinwheel, and the Pinwheel Cluster is M36.
- Butterfly: the Butterfly Nebula is NGC 6302, C69, also called the Bug Nebula, and it is also an old name for the Little Dumbbell, M76. The Butterfly Cluster is M6.
- Cat's Eye: the Cat's Eye Nebula is NGC 6543, C6, a planetary nebula; the Cat's Eye Galaxy is M94.
- Owl: the Owl Nebula is M97; the Owl Cluster is NGC 457, C13.
- Spindle: the Spindle Galaxy is M102 to some and NGC 3115, C53, to others, because Messier's own position for M102 is unclear.
Use the catalog number to search and the common name to talk
A catalog number names exactly one object, so it is the safe way to search an atlas, a planetarium app or the SIMBAD database at the Strasbourg astronomical data center. The convention is to use the oldest well-known number: the Messier number if there is one, then the Caldwell or NGC number, then IC and the specialist catalogs. Every object page on this site lists all the names it knows. See the catalogs for what each one covers.