History of the Discovery of the Deep Sky objects

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Since the earliest times, humans could view stars at night whenever it happened not to be cloudy. As in prehistoric times, there was barely no light polution in most regions of Earth, our ancestors could view stars of very faint light, and thus some of those objects we now summarize as Deep Sky Objects. This way, some of these objects are known as long as anything is known.

The most remarkable such "object" is certainly a galaxy, our own Milky Way; however we will not count this one here. Essentially the same is true for the most remarkable "moving" star cluster, the Ursa Major group, which consists of most of the stars in the famous "Big Dipper" asterism and makes up the more conspicous part of Ursa Major. These omissions are justified first because most people nowadays don't view them as "Deep Sky Objects", and second because their nature, i.e. that the Milky Way is a galaxy, and that the Ursa Major stars are a physical cluster, did not become apparent before modern times.

Some of the bright star clusters must also have been known very early, even before the time covered by any ancient records; these certainly include the Pleiades (M45) and the Hyades clusters in Taurus, which are conspicuous to the naked eye, and recorded early (i.e., the first certain document on the Pleiades is Hesiod, about 1000 BC). In the Southern Hemisphere, the two Magellanic Clouds (LMC -- the Large Magellanic Cloud, and SMC -- the Small Magellanic Cloud) were certainly known since earliest times, but not much recordings are preserved from the ancient Southerners.

It may be that Aristotle has recorded ancient observations of the open star cluster M41 in Canis Major around 325 BC; this would make this cluster the faintes object reported in ancient times. According to Burnham, based on the quote by P. Doig in 1925 of a statement made by J.E. Gore, it could be possible that Aristotle also observed M39 in Cygnus about that time, as a "cometary appearing object".

Hipparchus, the famous ancient Greek astronomer, did his observations from Rhodes between 146 and 127 BC. He was the first astronomer who compiled a catalog af stars; this work was perhaps triggered by the observation of a "New Star" (Nova) in the constellation Scorpius in 134 BC. He included two "nebulous objects" in his catalog, the Praesepe star cluster (M44) and the Double Star Cluster in Perseus, now called h+chi Persei (NGC 869+884, not in Messier's catalog).

Ptolemy, in his Great Syntaxas compiled 127--151 AD (better known as the Almagest), lists 7 objects, 3 of which are asterisms of little interest and not physical objects, two are those taken from Hipparchos (M44 and the Double Cluster in Perseus), but two are new: "A Nebula behind the Sting of Scorpius" which has now been identified as the conspicuous open cluster M7, which the present author has proposed to name "Ptolemy's Cluster", and the Coma Berenices Star Cluster, now cataloged as Melotte 111 (but not in Messier's catalog).

The first really "nebulous" object to be discovered and documented was the Andromeda Galaxy (M31), observed around 905 AD and documented 964 AD by the Persian astronomer Al Sufi in his Book of Fixed Stars. He also mentions a "nebulous star" little more than 2 degrees north of delta Velorum, which is most certainly the open cluster IC 2391, o Velorum. He also includes 6 of Ptolemy's objects, and a new "asterism" in Vulpecula (actually Brocchi's Cluster, Collinder 399, also nicknamed the "Coathanger Cluster"), so a total of 9 entries.

While not a deep sky discovery as the others mentioned here, the occurance of a supernova on July 4, 1054, was observed and recorded by Chinese and (very probably) by ancient North American astronomers; this supernova produced the Crab Nebula (M1), one of the most interesting deep sky objects.

No more new deep sky objects were discovered until Magellan, in 1519, reported the sighting of the Large and Small Magellanic Clouds. This brought the number of reported deep-sky objects to 11, although Al Sufi's work was not generally known at that time, before Galileo introduced the telescope into astronomy in 1609. At this event, Galileo revealed that Praesepe (M44) was not a nebula but a star cluster.

Nicholas-Claude Fabri de Peiresc (1580-1637) was the first to discover a true gaseous nebula, the Orion Nebula M42, in 1610, also the first deep sky discovery with a telescope. Jesuit astronomer J.-B. Cysatus (1588-1657) independently found M42 in 1611, but both discoveries of this object didn't get publicly known for a long time. Shortly after this, in 1612, Simon Marius (1570-1624) found (independently re-discovered) the Andromeda Galaxy (then Andromeda Nebula, M31).

Longly forgotten and rediscovered only in the early 1980s (published by Serio, Indorato, and Nastasi in the Journal of the History of Astronomy, No. 45 (February 1985) and No. 50 (August 1986)), Giovanni Batista Hodierna (1597-1660), astronomer at the court of the Duke of Montechiaro, compiled a catalog of some 40 entries, including 19 real nebulous objects, found with a simple Galilean refractor of magnification 20, and printed in Palermo in 1654. Included is an independent rediscovery of the Andromeda Nebula (M31), of the Orion Nebula (M42), and one of Brocchi's cluster, a first description of the Alpha Persei Moving Cluster, and at least 9 (probably 13 and perhaps 15) own true discoveries: M6, M36, M37, M38, M41, M47, NGC 2362, NGC 6231, and NGC 6530 (the cluster associated with the Lagoon Nebula M8), as well as probably M33, M34, NGC 752, and NGC 2451, and perhaps NGC 2169 and NGC 2175.

Christiaan Huygens' independent rediscovery of the Orion Nebula M42 eventually became widely known; he discovered three of the stars in the Trapezium Cluster which is embedded in this nebula.

Johan Hevel or Hevelke (known as Hevelius, 1611-87) from Dantzig compiled a catalogue of 1564 stars, Prodomus Astronomiae, published posthumously together with his star atlas, Uranographia. He included a list of 16 entries, 2 of which are objects (the Andromeda Galaxy M31 and the Praesepe star cluster M44), while the other 14 are asterisms or non-existent. Derham and Messier spent a lot of observing time to find these "nebulae"; among them is a double star in Ursa Major, which Messier believed to have been identified (it is M40) -- we now know that he probably he took another double star than Hevelius. Hevelius is also thought to have first seen M22, but the discovery of this first known globular cluster was generally assigned to Abraham Ihle in 1665.

In his star catalog Historia Coelestis Britannica, published in 1712 and revised in 1725, John Flamsteed (1646-1719) refers to several "nebulae" and "nebulous stars". This includes many of the then-known objects (Coma Cluster Mel 111, h+chi Persei, M31, M42) plus three independent discoveries, including re-discoveries of unknown Hodierna objects NGC 6530 (associated with M8) and M41 and his own true original discovery of NGC 2244 around the star 12 Monocerotis (associated with the Rosette Nebula NGC 2237-9, neither the cluster nor the nebula in Messier's catalog).

Gottfried Kirch (1639-1710), who was observing from Berlin, and known for his observations of stars and comets, discovered M11 in 1681 and M5 in 1702.

Edmond Halley (1656-1742) published a list of six "luminous spots or patches" in the Philosophical Transactions of the Royal Society for 1715, including his own discoveries of globular clusters Omega Centauri (on a journey 1677 at St. Helena) and M13 (1714), and the previously known objects M42, M31, M22, and M11.

Jean-Jacques Dortous de Mairan (1678-1771), before 1731, found a nebulosity around a star north of the Great Orion Nebula, which became known as M43 (this was published 1733). Shortly after this, John Bevis (1695-1771) discovered the Crab Nebula M1. He created a star atlas, which he called Uranographia Britannica, which was completed in 1750, but due to the bankrupt of the publisher, only one or two printings were produced, and the complimentary catalog was never published. Messier must have had access to a copy of this atlas, as he refers to the "English Atlas" several times, e.g. in the descriptions for the objects M1, M11, M13, M22, M31, and M35. Oddly, the discovery of M35 is ascribed to de Cheseaux in 1746 by Kenneth Glyn Jones, although it seems that Bevis might have seen it earlier, as it was in his atlas.

William Derham (1657-1735) published a list of 16 nebulous objects in the Philosophical Transactions of the Royal Society for 1733, 14 of them being from Hevelius' catalog, and the other two from Halley's list. Only two of the objects were real, M31 and M7, all others were nonexistent, or uninteresting asterisms, fooling other observers (including Messier) using this widespread compilation; it was reprinted in the Memoirs of the French Academy of Sciences in 1734, and included in de Maupertuis' book Discours sur la Figure des Astres in 1742.

About in 1746, Philippe Loys de Cheseaux (1718-51) observed several clusters and "nebulous stars", and compiled a catalog of their positions. According to Kenneth Glyn Jones and the Webb Society Deep-Sky Observer's Handbook, Vol. 3 (Open and Globular Star Clusters), 8 of them were original discoveries: IC 4665 (No. 2, maybe doubty), NGC 6633 (No. 3), M16 (No. 4), M25 (No. 5), M35 (No. 12, but see the remark at John Bevis), M71 (No. 13), M4 (No. 19), and M17 (No. 20). Moreover, he independently re-discovered M6 (No. 1), NGC 6231 (No. 9) and M22 (No. 17). De Cheseaux's list was given to Reaumur, who presented it to the French Academy of Sciences on August 6, 1746, but it was not otherwise published. It was investigated by Bigourdan in 1884 and became more wellknown only then. Besides observing nebulous patches in the sky, de Cheseaux was probably the first to formulate Olbers' paradox.

Jean-Dominique Maraldi (1709-88), also known as Maraldi II, discovered two globular clusters: M15 on September 7, 1746, and M2 on September 11, 1746.

Le Gentil (with his full name Guillaume-Joseph-Hyacinthe-Jean-Baptiste Le Gentil de la Galaziere, 1725-92) discovered M32, the Andromeda Galaxy's companion, on October 29, 1749. He also discovered the gaseous nebula M8, the Lagoon Nebula, in the same year (the cluster had been found previously by Flamsteed, see above). He independently found Hodierna's objects M36 and M38.

Abbe Nicholas Louis de la Caille (Lacaille, 1713-62) observed stars and Deep Sky objects in the Southern sky from South Africa during his 1751-52 journey, invented several southern constellations (many of which are still in use), and compiled a catalog of Southern Deep-Sky objects with 42 entries, 33 of which are real. Among them are 25 original and at least two independent rediscoveries. Lacaille's major original discoveries include the Eta Carinae Nebula NGC 3372, globular cluster 47 Tucanae (NGC 104), the Tarantula Nebula NGC 2070 in the Large Magellanic Cloud, and spiral galaxy M83, the first discovered galaxy beyond the Local Group.

This was the last discovery in the deep sky before Charles Messier (1730-1817) started to compile his catalog, and made his first original discovery of M3 in 1764. For more than a decade, Charles Messier was alone in looking for clusters and nebulous objects. During that time, he discovered 27 objects of which 25 are actually deepsky objects (the other two are the Sagittarius star cloud M24 and the double star M40).

Messier himself originally discovered 15 more nebulous objects (14 deepsky plus the star quartett M73) in the subsequent years until 1781.

In late 1774, Johan Elert Bode (1747-1826) joined those who looked for new nebulous objects with success: He discovered M81 and M82 on the last day of that year (December 31), and 3 more objects are subsequently quoted to him (M53 in 1775, M92 in 1777, and M64 in 1779). Bode compiled a deepsky catalog of 75 entries published 1777 in the Astronomisches Jahrbuch for 1779, and entitled "A Complete Catalogue of hitherto observed Nebulous Stars and Star Clusters". However, according to Kenneth Glyn Jones, this list was inflated by a lot of non-existent objects and asterisms gathered from Hevelius and elsewhere; it contains at most 50 real objects. The second edition, which was extended by his two latest original discoveries of M92 and M64, was published in 1780.

About five years later, in 1779, when Messier and Bode were still active in compiling their lists, four more astronomers entered the "club" of successful deepsky discoverers: Antoine Darquier de Pellepoix (Darquier, 1718-1802) of Toulouse discovered the Ring Nebula M57 in January, shortly before Messier; both found it when tracing a comet. Johann Gottfried Koehler (or Köhler, 1745-1801), who had independently found M81 and M82 in the time between 1772 and 1778 (so maybe he did it before Bode), had discovered M67 this year or perhaps earlier, and found M59 and M60 on April 11, 1779, when tracing comet Bode 1779. While Messier found, in addition, M58 on that occasion, it was Barnabus Oriani (1752-1832) who first discovered M61. Koehler published a catalog of 20 entries in 1780. Finally, Messier's friend Pierre Mechain (1744-1804) began his astronomical observing career, and made his first original discovery of M63 on June 14, 1779. Subsequently, Mechain discovered originally about 29 objects most of which he contributed to Messier's catalog, as he was observing in close cooperation with Charles Messier. As he surely has communicated all his discoveries to Messier, Helen Sawyer-Hogg, in 1947, decided to add three more of them to the Messier catalog (M105 to M107).

As a major milestone in deepsky discovery, the Messier Catalog was published in its final version of 103 objects in 1781 in the Connaissance des Temps for 1784. More recent additions from Messier's personal notes and Mechain's discoveries brought it to 110 entries, which all belong to real objects (though four of them were missed for over a century, and there is still some controversy about M102). It contains the majority of all clusters, nebulae, and galaxies known up to April, 1782, when M107 was the last Messier object to be discovered (by Pierre Mechain).

The Messier catalog did in particular impress the great German-British astronomer Friedrich Wilhelm (William) Herschel (1738-1822), who by that time had become famous especially because of his discovery of planet Uranus in 1781. Herschel received his copy of Messier's catalog from a friend, William Watson, on December 7, 1781. At that time, he was still working as organist at Bath (which he gave up in May, 1782), and a skilled telescope maker. He started an extensive scan of the skies he could observe from England (i.e., the northern sky), with large telescopes of up to a 48-inch aperture, 40-foot focal length giant which he set up himself on August 28, 1789 (on that first day he discovered Saturn's moon Enceladus with this new scope). Published in 3 steps, Herschel cataloged over 2500 discoveries, most of which are real deepsky objects. As he had the best telescope of that time, he was without competition. He was assisted by his sister Caroline Lucretia Herschel (1750-1848) who was an avid observer herself; she discovered a lot of the clusters and nebulae in Herschel's catalog (among them is an independent discovery of M110 = H V.18, which Messier had discovered but not cataloged 10 years earlier, and an independent rediscovery of the missing Messier open cluster M48 = H VI.22), and discovered 8 comets.

William Herschel classified the nebulous objects in eight groups:

  1. Bright Nebulae
  2. Faint Nebulae
  3. Very faint Nebulae
  4. Planetary Nebulae
  5. Very large Nebulae
  6. Very compressed and rich star clusters
  7. Compressed clusters of small and large (i.e., faint and bright) stars
  8. Coarsely scattered clusters of stars
As the true nature of the objects was still unknown at that time, this classification is more of historical importance today.

William (and Caroline) Herschel had virtually exhausted the northern skies with object discoveries around 1800. But the southern sky was still waiting to be explored, and it was James Dunlop (1795-1848) who made the first major observations there after Lacaille. He went to New South Wales, Australia, in 1821, accompanying a Sir Thomas Makdougall Brisbane, He was keeper of the Brisbane observatory at Paramatta, 1823-1827, and compiled a star catalog (the Brisbane Catalogue of over 7000 southern stars). His observations of deepsky objects from that time were compiled to "A Catalogue of Nebulae and Clusters of Stars in the Southern Hemisphere observed in New South Wales" of about 600 discovery entries. This catalog was sent to William Herschel's son, John Herschel, who presented it to the Royal Society in 1827. Dunlop was awarded for this work with the Gold Medal of the Royal Astronomical Society, and with Lalande Medal of the French Academy. However, this did not prevent a lot of his "objects" to be nonexistent, or so badly described that they couldn't be safely identified later: Only about half his entries can be related to real objects.

John Frederick William (John) Herschel (1792-1871) had continued his father's work, and added 525 new entries (northern objects) in a catalog published in 1833. But John Herschel also wanted to catalog the southern skies. On November 13, 1833, he and his family went on ship to sail to the Cape of Good Hope, South Africa, where they arrived on March 4, 1834. He intensively studied the southern skies in the subsequent years. His observations of southern nebulous objects were published in 1847 as a catalog with 1713 entries. Evidently, he summarized his and his father's, as well as others' deepsky discoveries in his great General Catalogue of over 5000 entries.

The work of the Herschels finally brought the great "nebula" (and cluster) discovery time to a conclusion. Nevertheless, it took time and new research methods (especially photography and spectroscopy), until the nature of the various deepsky objects was uncovered: The gaseous nature of the "true" nebulae was discovered by the British amateur and pioneer of spectroscopy William Huggins (1824-1910) in the late 19th century, while only in the 1920s the true nature of galaxies as independent "island universes" like our Milky Way became apparent (due to the work of Edwin Hubble (1889-1953)).

Historic Deep Sky Catalogs

Listed are the historic catalogs in chronological order; the number of objects and, if different, the number of entries (including those which do not correspond real objects) is given in parentheses.
134--127 BC (2)
Hipparchos included two nebulous objects in his star catalog: M44 and h+chi Persei (NGC 869+884, not in Messier's catalog).
127--151 AD (4/7)
Ptolemy's Almagest contains a list of 7, 4 of which are real: M44 and h+chi Persei from Hipparchos, and M7 (proposed "Ptolemy's Cluster") and the Coma Berenices star cluster Melotte 111 (not in Messier's catalog). Ptolemy's Almagest is available online at Nasa's ADC.
964 AD (6/9)
Al Sufi lists two new objects in his Book of Fixed Stars: M31 and o Velorum = IC 2391 (not in Messier's catalog), in a list of totally 9 (including 6 entries from Ptolemy).
15th century (4/7)
Ulegh Begh from Samarkand compiled a new star catalog, containing the objects listed by Ptolemy.
1590 (1/7)
Tycho Brahe completed a catalog of 777 stars in 1590, which contained 7 nebulous objects, 6 of which are uninteresting asterisms, and M44.
1654 (19/~40)
Giovanni Batista Hodierna published a list of ~40 entries, 19 of which correspond to real objects, including an independent re-discovery of M31 and own true discoveries of M6, M36, M37, M38, M41, M47, and NGCs 2362, NGC 6231, NGC 6530 (associated with M8), as well as probably M33, M34, NGC 752, and NGC 2451, and perhaps NGC 2169 and NGC 2175. This list got lost until its rediscovery in the early 1980s.
1690 (2/16)
Johan Hevel (Hevelius) included, in his Prodomus Astronomiae, a list of 16 entries, including M31 and M44, plus 14 asterisms. Looking for one of those, Messier cataloged the double star M40.
1712, revised 1725 ("several")
John Flamsteed referred to several "nebulae" and "nebulous stars" in his star catalog Historia Coelestis Britannica. 3 independent discoveries, including re-discoveries of unknown Hodierna objects NGC 6530 (associated with M8) and M41 and his own true original discovery of NGC 2244 around the star 12 Monocerotis (associated with the Rosette Nebula NGC 2237-9, neither the cluster nor the nebula in Messier's catalog)
1715 (6)
Edmond Halley published a list of 6 "luminous spots or patches":
  1. in Orion: The Orion Nebula M42
  2. in Andromeda: The Andromeda Galaxy M31
  3. in Hercules: Globular Cluster M13 (Halley's own discovery 1714)
  4. in Sagittarius: Globular Cluster M22
  5. in Antinous (Scutum): Open Cluster M11
  6. in Centaurus: Globular Cluster Omega Centauri (NGC 5139; Halley's own discovery 1677)
1733 (2/16)
William Derham published a list of 16 entries, two of which are objects (M31 and M7). Published in the Philosophical Transactions of the Royal Society for 1733
1746 (18/20)
Philippe Loys de Cheseaux compiled a list of 21, 8 of which are original discoveries: No. 2 = IC 4665 (maybe doubty), No. 3 = NGC 6633, No. 4 = M16, No. 5 = M25, No. 12 = M35, No. 13 = M71, No. 19 = M4, and No. 20 = M17, and three are independent re-discoveries: No. 1 = M6, No. 9 = NGC 6231 and No. 17 = M22.
1755 (34/42)
Abbe Nicholas Louis de la Caille (Lacaille) published his catalog of Southern Deep-Sky objects of 42 entries, 9 of which are errata and asterisms, but 33 are real objects, in the Memoirs of the French Royal Academy. Lacaille classified these objects according to their appearance in his scope in three classes: I, Nebulae; II, Nebulous Star Clusters; III, Nebulous Stars. This classification is hardly anyhow related to physical object classes though.
1771 (45)
Charles Messier publishes the first version of his catalog in the Memoirs of the Royal Academy of France.
1777 (<~50/75)
Johann Elert Bode publishes a catalog of 75 entries
1780 (<~52/77)
Johann Elert Bode's catalog's second edition was extended by two to 77 entries.
1780 (20)
Johann Gottfried Koehler
1780 (68)
Charles Messier publishes an updated version of his catalog, extended to 68 objects.
1781 (103)
Charles Messier publishes the final version of his catalog in the Connaissance des Temps for 1784. Later additions were finally added to this catalog in the 20th century, and bring this compilation to 110 entries. Contrary to most other compilations, there is a real object for each entry, perhaps with one exception only (M102).
1786, 1789, and 1802 (2397/2514 [2520])
Friedrich Wilhelm (William) Herschel, in an extensive scan with the best available instruments, compiled his comprehensive catalog of 2500 deep sky objects published in three steps, in the Philosophical Transactions of the Royal Society of England. Similar to Lacaille, William Herschel divided his entries in object classes, I--VIII, so that numbers are given by, e.g., 215 H I, H I.215, H 215-1, or in a similar way. His classes are much more descriptive and more useful, although, as the nature of most objects still had to be uncovered, his classification is merely of historical importance.
1827 (<~290/629)
James Dunlop publishes his compilation, "A Catalogue of Nebulae and Clusters of Stars in the Southern Hemisphere observed in New South Wales" (printed in the Philosophical Transactions of the Royal Society for 1828). Unfortunately (especially for John Herschel) many of these objects were badly described and could not be verified, or were nonexistent. John Herschel, who could only identify 211 of them, quotes Dunlop's objects as Delta 1 -- Delta 629, some others as Dun 1 -- Dun 629.
1833 (/2307)
John Herschel publishes a catalog of nebulous objects he observed from England, containing about 525 newly discovered objects, and many of William Herschel's as well as all Messier objects recognized at that time. This catalog was printed in the in the Philosophical Transactions of the Royal Society for 1833. The entries in this catalog are usually quoted as h 1 -- h 2307.
1847 (/1713)
John Herschel publishes his Cape of Good Hope observations in the book: Results of Astronomical Observations made during the years 1834, 5, 6, 7, 8 at the Cape of Good Hope, being a completion of a telescopic survey of the whole surface of the visible heavens commenced in 1825. Smith, Elder & Co., London. The 1713 entries in this catalog were numbered in continuation of John Herschel's 1833 catalog, and are normally referred as h 2308 -- h 4021.
1864 (/5079)
John Herschel publishes his General Catalogue, as Catalogue of Nebulae and Clusters of Stars, in the Philosophical Transactions of the Royal Society (London), Vol. 154, p. 1-137 (1864). Objects are numbered GC 1 -- GC 5079, with GC 1 to 5063 ordered by right ascension, the rest added as supplement.
1867 (500)
Heinrich Louis d'Arrest
1887 (/7840)
John Louis Emile Dreyer, New General Catalogue
1895 (/1530)
John Louis Emile Dreyer, Index Catalogue, IC I
1907 (/5836; new: /4306)
John Louis Emile Dreyer, Index Catalogue, IC I+II (part II appeared as Second Index Catalog). This brought the number of entries in NGC and IC to 13676, of which some are erroneous though.


Thanks to Glen Cozens for communicating some acurate data on James Dunlop.


Hartmut Frommert (spider@seds.org)
Christine Kronberg (smil@lrz.uni-muenchen.de)

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Last Modification: 6 May 1999, 9:50 MET