Two and a half centuries ago a French comet hunter named Charles Messier began compiling a catalogue of nebulous sky objects. He explained his motivation in the French almanac Connaissance des Temps for 1801:

Messier died long before twentieth-century astronomers realized the profound nature of these hauntingly diffuse glows. The 110 “Messier objects,” it turns out, are an eclectic collection of celestial treasures: 39 galaxies, 57 star clusters, 9 nebulae, a supernova remnant, a swath of Milky Way, a tiny grouping of stars, a double star, and even a duplication. The list includes the most massive and luminous galaxy known, the ghostly remains of a cataclysmic stellar explosion, and an immense cosmic cloudscape that cradles newborn stars in dense cocoons of hydrogen gas.

Every Messier object is within reach of a small telescope, and many are visible with binoculars and the naked eye, especially under clear, dark skies far away from city lights. Amateur astronomers of all ages enjoy tackling the Messier catalogue members, because they represent a good sampling of what’s “out there,” and because finding them helps to hone observing skills. In a sense, the Messier objects are the testing grounds for budding skywatchers.

This book is your companion under the stars. Similar to a field guide to birds, insects, or flowers, this book will help you locate and identify the Messier objects – the most famous deep-sky splendors visible from the Northern Hemisphere. It contains, among other things, finder charts to help you locate them, photographs, pencil drawings of their telescopic appearance, detailed descriptions, and descriptions of other interesting celestial sights near them. I have also included a lineup of some of my favorite non-Messier objects.

Each Messier object section opens with a photograph and some essential data, including the object’s coordinates, magnitude, apparent size, and distance. Descriptions of the object from a translation of Charles Messier’s original catalogue and from the New General Catalogue of Nebulae and Clusters of Stars (1888) or the two subsequent Index Catalogues (1895 and 1908) follow. These data and descriptions should help you realize what to expect when you first glance at a Messier object through the eyepiece.

The objects are ordered as Messier catalogued them. However, you can view them in any order you wish, as long as a particular object is above the horizon when you plan to observe it. Use a star wheel or an astronomy app to determine which constellations, and therefore which Messier objects, are visible on the date and time of night you want to look.

Cambridge University Press first published Deep-Sky Companions: The Messier Objects 15 or so years ago. It was the first in what is now a series of five Deep-Sky Companions volumes. The other books in the series are subtitled The Caldwell Objects, Hidden Treasures, The Secret Deep, and Southern Gems. Not only was The Messier Objects the first book in this series, but it was also the first deep-sky book I had ever written. As such it stands apart from the other volumes for several reasons.

First, many observers already had in their possession one or more books on the Messier objects, most notably The Messier Album by the late John H. Mallas and Evered Kreimer (Sky Publishing, Cambridge, MA, 1978), segments of which first appeared in Sky & Telescope magazine in the late 1960s, and Messier’s Nebulae and Star Clusters, 2nd edition, by the late Kenneth Glyn Jones (Cambridge University Press, 1991). Thus, I realized, my book would need a fresh approach.

For instance, to me, the most outstanding aspects of Glyn Jones’s book are the rich histories he presents on Messier and his contemporaries, as well as his summaries of historical observations of the “M” objects. Not wanting to duplicate this ef ort, I decided to minimize those aspects in my own book. I saw the Mallas and Kreimer book as having three strengths: (1) Kreimer’s beautiful photographs of the Messier objects taken through his 12 1/2-inch Cave rel ector from Prescott, Arizona; (2) Mallas’s pencil drawings of each M object as seen through a 4-inch f/15 Unitron refractor from his backyard in Covina, California; and (3) Harvard historian Owen Gingerich’s scholarly biography of Messier and his contemporary Pierre Méchain.

One mystery that still haunts the halls of astronomy is why the eighteenth-century French comet hunter Charles Messier did not include the Double Cluster in his famous catalogue. “This splendid object … was certainly known in his day,” Robert Burnham Jr. comments in his Celestial Handbook, “and he included other bright clusters such as the Praesepe and the Pleiades.” So why not the Double Cluster? It’s possible that Messier had a very logical reason to omit it. But first a powerful myth must be dispelled.

The Messier catalogue is not a list of the best or the brightest deep-sky objects in the heavens – a common misconception that is the astronomical equivalent of saying a bat is blind. Just as bats are not blind, Messier’s catalogue is not a manifest of celestial superlatives. But who hasn’t loosely described the Messier objects as the finest in the heavens? In his jacket copy for The Messier Album, for instance, Professor Owen Gingerich encourages readers to “find a telescope and a clear night, and begin the chase of the most spectacular sidereal objects of the northern skies.”

Without question, the Messier catalogue contains some of the most spectacular deep-sky objects visible in small telescopes. But their inclusion is largely circumstantial. Messier never intended to create a list of the most spectacular objects in the heavens. His was a catalogue of “comet masqueraders,” as the late comet discoverer Leslie Peltier called them.

At the end of his catalogue in the Connaissance des Temps for 1784, Messier included a list of objects reported by other astronomers that he had been unsuccessful in locating himself. The list, translated from French by Storm Dunlop, follows. As was his custom, Messier refers to himself in the third person.

Nebulae discovered by various astronomers, which M. Messier has searched for in vain.

Each spring, amateur astronomers around the world run a marathon – not the grueling 26-mile-long race but a visual race through the night sky to glimpse all 109 Messier objects in a single night. Messier marathons, as they are called, are held during late March and early April, the only time of the year when all the Messier objects are visible between dusk and dawn, and the only time of year when the Sun lies in a region of sky devoid of these celestial treasures. On the first clear, moonless night, marathoners start searching low in the western sky at dusk and then hop from one Messier object to the next until they’ve exhausted all the objects (or themselves) by dawn. Aside from clear skies, success requires a decent knowledge of the stars and constellations, efficient use of a telescope, and the ability to read star charts and confirm the appearance and position of each Messier object. These skills prove critical especially during twilight hours, when inevitably some targets must be found.

To the best of my knowledge, the Messier marathon originated in Spain, when a group of amateur astronomers set out to attempt the task in the 1960s. Several amateur astronomers across the globe independently conceived the notion a decade later. In the March 1979 issue of Sky & Telescope magazine, the late Deep-Sky Wonders columnist Walter Scott Houston described how, in the United States, Tom Hoffelder of Florida began marathoning with amateurs in the mid-1970s, while the Amateur Astronomers of Pittsburgh independently started the activity in 1977. On the West Coast, Donald Machholz, a leading comet discoverer, dreamed up the marathon idea in September 1978. Needless to say, serendipity struck like wildfire, and the activity spread worldwide. Today, astronomy clubs routinely sponsor Messier marathons, as well as variations on the theme, such as binocular marathons, CCD-imaging competitions, and CCD versus visual showdowns. One club even puts on a Messier event in which amateur astronomers compete in a cycling race, stopping occasionally to hunt down Messier objects with portable telescopes!

Charles Messier is best remembered for the objects he largely tried to avoid and help others avoid. Messier was first and foremost a comet hunter, and he dedicated clear, moonless nights to this pursuit. He was quite successful in his search, having found some 15 comets, though only 12 bear his name (with some exceptions, comet names were not officially used until the twentieth century). In his time, comet hunting was intensely competitive, and Messier was inspired not only by the search but also by the fame new comet discoveries would bring him. The fuzzy, noncometary objects he encountered intrigued him, in part, because they fooled him, if only briefly. Messier created his renowned catalogue largely to benefit comet hunters, so they would not confuse these nebulous glows with comets. But it’s also possible Messier knew he would reap fame by discovering new nebulae.

Messier’s first list of 45 objects, published in the Memoirs of the French Academy of Sciences for the year 1771, was well received by his friends and colleagues. In the introduction to the work, astronomer Jerome de Lalande praised Messier, saying the task could only have been undertaken by an indefatigable and experienced observer. William Herschel, in particular, regarded Messier’s catalogue as an excellent collection of clusters and nebulae, and it apparently prompted Herschel to undertake his own search for similar deep-sky objects. (Herschel employed much larger telescopes in his survey, which led to the additional discovery of more than 2,000 objects.) Nevertheless, legitimate questions can be raised about why certain objects made it into Messier’s catalogue and other seemingly obvious ones did not.

The purpose of this chapter is to help new observers get started. (If you’re a seasoned observer, you may want to skip to the next chapter, though you should read the section on “Observing Tips” before you do.) It contains enough essential information to help you find a few Messier objects. There is no avoiding the need to learn sky directions, recognize the major constellations and their brightest stars, know how to use a star map, and understand how the sky changes with the seasons. You can teach yourself just about all these things with a star wheel, or planisphere. These special sky maps are inexpensive, fun and easy to use, and very educational. (Star wheels can be purchased at any nature store or planetarium gift shop.) To purchase the proper star wheel, you will need to know your latitude on Earth so you can determine which stars are visible from your location. Consult a world atlas at your local library. You could also use one of the more popular Apps available online, such as Star WalkTM.

Although anyone can enjoy this book, the following section on sky orientation and many references to sky directions throughout the book are targeted primarily for observers at mid-northern latitudes. Observers in the far south will not be able to see several of the most northerly Messier objects. Chapter 6, however, describes many southerly objects either missed or ignored by Messier. A good supplementary guidebook for southern observers is my Deep-Sky Companions: Southern Gems. Otherwise, the material in this book, especially the descriptive notes on the Messier objects, can be used by all.