Messier object

Lore & Background

A preliminary version of the catalogue first appeared in 1774 in the Memoirs of the French Academy of Sciences for the year 1771. The first version of Messier's catalogue contained 45 objects, which were not numbered. Eighteen of the objects were discovered by Messier; the rest had been previously observed by other astronomers. By 1780 the catalogue had increased to 70 objects. The final version of the catalogue containing 103 objects was published in 1781 in the Connaissance des Temps for the year 1784. However, due to what was thought for a long time to be the incorrect addition of Messier 102, the total number remained 102. Other astronomers, using side notes in Messier's texts, eventually expanded the list to 110 objects. The catalogue consists of a diverse range of astronomical objects, from star clusters and nebulae to galaxies. For example, Messier 1 is a supernova remnant, known as the Crab Nebula, and the great spiral Andromeda Galaxy is M31. Further inclusions followed. Messier lived and conducted his astronomical work at the Hôtel de Cluny (now the Musée national du Moyen Âge), in Paris, France. The list he compiled contains only objects found in the sky area he could observe from the north celestial pole to a celestial latitude of about −35.7°. He did not observe or list objects visible only from farther south, such as the Large and Small Magellanic Clouds.

Reader's Guide

The Messier catalogue comprises nearly all of the most spectacular examples of the five types of deep-sky object – diffuse nebulae, planetary nebulae, open clusters, globular clusters, and galaxies – visible from European latitudes. Furthermore, almost all of the Messier objects are among the closest to Earth in their respective classes, which makes them heavily studied with professional class instruments that today can resolve small and visually significant details in them. A summary of the astrophysics of each Messier object can be found in the Concise Catalog of Deep-sky Objects. Since these objects could be observed visually with the relatively small-aperture refracting telescope (approximately 100 mm ≈ 4 inches) used by Messier to study the sky from downtown Paris, they are among the brightest and thus most attractive astronomical objects (of the class popularly called deep-sky objects) observable from Earth, and are popular targets for visual study and astrophotography available to modern amateur astronomers using larger aperture equipment. In early spring, astronomers sometimes gather for 'Messier marathons', when all of the objects can be viewed over a single night.

Did You Know?

• The first edition of the catalogue in 1774 contained 45 objects, which were not numbered.
• M102 was observed by Méchain, who later concluded it was a re-observation of M101, though some sources identify it as NGC 5866.
• The catalogue was expanded to 110 objects through additions by Nicolas Camille Flammarion, Helen Sawyer Hogg, Owen Gingerich, and Kenneth Glyn Jones.

A Comet Hunter's Frustration

The Messier catalogue was born not from a desire to survey the heavens comprehensively, but from a very practical frustration. Charles Messier, a French astronomer working from the Hôtel de Cluny in Paris (the building that today houses the Musée national du Moyen Âge), was primarily a comet hunter. Each time he spotted a fuzzy patch of light through his modest refracting telescope—roughly 100 millimetres in aperture—he had to determine whether it was a new comet or merely a fixed object he had already catalogued. To spare himself and fellow observers that repeated confusion, he began compiling a list of non-comet objects that kept muddying his search. He carried out this work alongside his assistant Pierre Méchain, and the resulting document, titled Catalogue des Nébuleuses et des Amas d'Étoiles, was essentially a do-not-confuse register. Because Messier observed only from European latitudes, his sky stretched from the north celestial pole down to roughly −35.7° celestial latitude, meaning southern-only targets like the Magellanic Clouds never made the list.

From Forty-Five to One Hundred and Ten

What began as a modest 45-entry list in 1774 grew steadily into one of astronomy's most enduring references. The preliminary edition, published in the Memoirs of the French Academy of Sciences for 1771, contained 45 unnumbered objects—18 of them Messier's own discoveries, the rest drawn from earlier work by other astronomers. By 1780 the count had reached 70, and the definitive 103-object version appeared in 1781 within the Connaissance des Temps pour l'Année 1784, France's official yearly ephemeris publication. Marginal notes left by Messier and Méchain, however, hinted at additional objects they had known about but never formally listed. Nicolas Camille Flammarion was the first to act on such a clue, adding M104 in 1921 after spotting a note in a copy of the 1781 edition. Helen Sawyer Hogg contributed M105 through M107 in 1947, Owen Gingerich added M108 and M109 in 1960, and Kenneth Glyn Jones appended M110 in 1967, bringing the total to 110. The enigmatic M102, originally recorded by Méchain, was long dismissed as a duplicate of M101, though some scholars propose it may actually be the galaxy NGC 5866.

A Universe in One List

The catalogue's true strength lies in its remarkable diversity. Rather than focusing on a single class of object, it spans the full spectrum of deep-sky phenomena visible from European latitudes: diffuse nebulae, planetary nebulae, open star clusters, globular clusters, and galaxies. At one end of the range sits M1, the Crab Nebula, a supernova remnant tracing the aftermath of a stellar explosion. At the other, M31, the great spiral Andromeda Galaxy, looms as one of the most iconic targets in the night sky. What unites these vastly different targets is their proximity and brightness. Almost every Messier object ranks among the nearest examples of its particular class, which is precisely why they have become prime subjects for professional telescopes capable of resolving fine structural detail. The Concise Catalog of Deep-sky Objects compiles a summary of the astrophysics behind each entry, and the sheer variety—from glowing nebular gas to entire spiral galaxies—makes the list an almost perfect survey of the universe as seen from Earth's Northern Hemisphere.

A Living Guidebook for Stargazers

Few astronomical catalogues have achieved the cultural penetration of the Messier list. More than two and a half centuries after its creation, objects across the sky are still routinely identified by their M-numbers in both professional literature and casual conversation among stargazers. The reason for this enduring popularity is practical: because Messier selected objects bright enough to be seen through a roughly 100-millimetre refractor from downtown Paris, they remain among the most visually rewarding deep-sky targets available to anyone with a modest telescope. Modern amateur astronomers, armed with larger-aperture instruments, find them ideal for both visual observation and astrophotography. In early spring, a special tradition called the Messier marathon draws dedicated observers who attempt to locate all 110 objects within a single night, exploiting the seasonal geometry that places every entry above the horizon simultaneously. The catalogue thus functions not merely as a historical document but as a living guidebook, connecting today's backyard stargazer to the same patch of sky that Messier and Méchain scanned from the Hôtel de Cluny in the eighteenth century.