Astronomical Catalogues

Astronomical objects are generally identified by their catalogue names, like Messier 1, NGC 1952, SH2-244 oder LBN 833. In this case these identifiers all point to the same object, the Crab Nebula in constellation Taurus.

But why there are so many different catalogues and where do these originate from?

I'll try to provide a rough tour through the history of astronomical catalogues of deep sky objects. I do not claim completeness, in fact all star catalogues are omitted. For a more complete overview please check out the List of astronomical catalogues at Wikipedia.

The Messier Catalogue

The probably most popular catalogue in astronomy was compiled back in the 18th century by french astronomer Charles Messier. His intention was not to obtain a collection of interesting objects in the sky, but exactly the opposite. As a passionate comet "hunter" he continuously spotted some similar looking diffuse objects, which do not move in relation to the stars. To not waste observation time on these "annoying" things, he added their coordinates to his catalogue of nebulae and star clusters. With telescopes available in that timeframe it was not possible to classify these objects any further.

Along with own discoveries Charles Messier added objects from several other contemporary astronomers as well. The third and last version of his catalogue containing 103 objects was published in 1784. This was later expanded to 110 objects based on notes found on Messier's documents.

You'll find images of all 110 Objects in my Normalized Messier Catalogue.

The Messier Catalogue is still relevant today, since it contains primarily bright objects, observable even with smaller telescopes. But since several objects are quite small, for example distant galaxies, a larger focal length is beneficial.

Herschel Family

Frederick Wilhelm Herschel, his sister Caroline Herschel and later his son John Herschel were passionate astronomers and their collections of deep sky objects set the foundation of the modern New General Catalogue.

One of Wilhelm Herschel's greater discoveries was planet Uranus in 1781 and the associated ring system in 1797. Additionally he discovered several moons orbiting Uranus and Saturn and tried to find a correlation between sun spot activity and the terrestial weather.

After studying Messier's catalogue he gained interest on these nebulous objects and using his powerful telescopes he could resolve several into stars. Conforming the former assumtion, these could be star clusters. Classification of galaxies and nebulae was still not possible.

Herschel discovered about 2500 of these objects and finally released his Catalogue of Nebulae and Clusters of Stars in 1802.

His son John Herschel continued his father's work and discovered, for example, that the Magellanic Clouds in fact consists of countless stars. In addition to smaller astronomical catalogues created at his residences (Slough Katalog 1833, Cape Katalog 1847), he published the General Catalogue of Nebulae and Clusters with more than 5000 entries in 1864. This was essentially the base of the New General Catalogue.

New General Catalogue and Index Catalogue

The danish astronomer John Louis Emil Dreyer, also known as Johan Ludvig Emil Dreyer, studied these diffuse objects for years until he finally consolidated his own discoveries with collections and catalogues of other astronomers and released the New General Catalogue of Nebulae and Clusters of Stars in 1888.

Containing 7840 entries this catalogue is still a main reference nowadays with the omnipresent prefix NGC. In direct comparison with Messier's catalog, the NGC contains a large quantity of smaller objects, primarily distant galaxies, which could not have been observed hundred years before.

After release of the NGC, Johan Dreyer published another two supplemental collections containing additional 5000+ objects and called these Index Catalogues. Their entries use the prefix IC.

Barnard's Catalogue

Around 1900 the US american astronomer Edward Emerson Barnard studied areas of non glowing matter within the Milkyway using photographic methods. The Barnard Catalogue counts a total of 349 dark nebulae.

Most of these are located in front of starfields. More obvious ones are located within or in front of emission nebulae, like the distinctive Horsehead Nebula B33 in constellation Orion.

Sky Surveys or "Durchmusterungen"

Already during the 19th century several systematic visual surveys of the night sky were performed. The "Bonner Durchmusterung" took 17 years, mapped about 300.000 stars of the nothern sky and was released in 1863. The "Córdoba Duchmusterung" taken between 1892 and 1914 added nearly 600.000 stars of the southern sky. I do have a great respect for the effords mapping out about a million stars visually.

With enhancements in photography and availability to mechanically compensate telescope orientation for the rotation of earth, astro photography started and Henry Draper took the first photographic image of the Orion Nebula in 1880.

During the years 1948 to 1956 the first Palomar Observatory Sky Survey (POSS-I) was performed and imaged a large patch of the sky in both red and blue wavelengths which allows a rough estimate on the spectral distribution. During the 1980s the sky survey was repeated (POSS-II) with a more powerful telescope and additionally imaged infrared wavelengths.

The photographic plates were digitized in the 1990s and provided to the public by the Space Telescope Science Institute through their portal The STScI Digitized Sky Survey. The image above this section was generated from the POSS-II data, consequently the source data is copyright by MAST.

While these sky surveys do not directy represent a catalogue, several current catalogs are based on the images from the POSS-I.

Sharpless Catalogues

Based on the first Palomar Observatory Sky Survey (POSS-I) the US-american astronomer Stewart Sharpless in 1953 published a first list of areas, where he expected strong emissions in H-Alpha. Entries in this catalogue are prefixed with SH1 and use the coordinate system of epoch 1855, since the star reference used was the Bonner and Córdobaer Durchmusterung.

The second release of the Sharpless Catalog was released in 1959 and contains 312 objects. The entries now use prefix SH2 and relate to the coordinate system of epoch 1900.

The image above shows the Tadpole Nebula SH2-236 on the left and a larger patch of H-Alpha towards the right, named SH2-230.

Lynds' Catalogues of Dark/Bright Nebulae

Around 1960 rhe US american astronomer Beverly Lynds (sadly there is no bio available on Wikipedia) created two catalogues based on the POSS-I images, one focusing on bright, the other on dark nebulae. But the meaning of "bright" and "dark" probably differs from the expected.

Lynds' Catalogue of Dark Nebulae (LDN) is similar to Barnard's intend and contains dense patches obscuring the background, like the brownish patch in the image above, named LDN 1295. Another example would be LDN 1064 in the image from the Palomar Observatory above.

In contrast Lynds' Catalogue of Bright Nebulae (LBN) lists patches in the sky which are brighter than the background. The luminosity of these objects are kind of dynamic. Some of them may be visually observed even with smaller telescopes, like LBN 974, the Orion Nebula. Others are quite faint and barely perceptible on the photographic plates, like patches of dust illuminated by the whole galaxy, the Integrated Flux Nebulae. An example is LBN 691.

Van den Bergh Catalogue

Another astronomer using the plates from the Palomar Observatory Sky Survey (POSS-I) was Sidney van den Bergh. In 1966  he published a cataloge containing 159 reflection nebulae.

The image above shows VdB 139 the core of the Iris Nebula. The title image of Barnard's catalogue contains VdB 51 on the left.

Abell Catalogue

Using a magnifying glass the US american astronomer George Ogden Abell searches the red photographic plates of the POSS-I for galaxy clusters. The initial release of the Abell catalog of rich clusters of galaxies in 1958 contains about 2700 such clusters containing at least 50 galaxies. After adding clusters from the southern sky in 1989, the catalogue now contains more than 4000 entries.

The image shows Abell 1656, the Coma Cluster in constellation Coma Berenices. It contains over 1000 galaxies and most of the dots in this image are indeed galaxies not stars.

Caldwell Catalogue

The english astronomer Sir Patrick Caldwell-Moore assembled a list of interesting objects which could be observed from smaller telescopes. The Caldwell Catalogue does not contain new objects but serves as a guide to 109 objects of interest.

Released in 1995 this is the youngest catalogue containing deep sky objects.

The image shows C34, the western part of the Veil Nebula, a supernova remainder.