The present work deals with the discovery, visual observation, description and cataloguing of nebulae and star clusters in the 19th century. Central is the question, why they were searched and what resulted from the numerous studies and catalogues for the development of astronomy. Involved are astronomers, instruments, sites and a large number of objects.
The matter, which starts with William and John Herschel, climaxed
with the "New General Catalogue" (NGC) of John Louis Emil Dreyer.
Its history shows, what could be achieved with the methods of the time, to realize
the spatial arrangement, nature and evolution of nebulae and clusters. The moment
of its publication in 1888 roughly coincides with the transition from classical
astronomy, focused on visual observations and position measurements, to modern
astrophysics, represented by spectroscopy, photography and photometry.
With the NGC the Danish descending Dreyer has compiled the last comprehensive "visual" catalogue, containing all types of non-stellar objects in the whole sky. It has kept its importance over the years and NGC-numbers are still essential elements of professional astronomy. The objects are among the primary research targets: Their moderate magnitudes and sizes allow astrophysical studies even with small telescopes - and with the largest, extreme details appear.
The immense scale of the theme has - opposite to the popular Messier catalogue with its just 103 entries - obviously inhibited a comprehensive historic approach; only a few limited aspects were investigated. The work is focused on the 7840 NGC-objects (from which over 2000 are presented in tables and figures). The history of their discovery was reconstructed from the original observations. Many can already be found in earlier catalogues and listings, published by Messier, William Herschel, John Herschel, Auwers, Dreyer and others. To obtain a chronologically consistent picture, not only the NGC, but also its various forerunners were critically analysed. Modern object data, representing the real sky, were used as reference. The basic source is the "Revised New General and Index Catalogue", compiled by the author.
Concerning the discoverers, around 100 persons are involved, spread over many countries. Their biographies, observations, sites, instruments publications and success rates are presented in detail. Unfortunately Dreyer has given only sparse information. Thus revealing backgrounds and sources, required extensive research; numerous original sites and libraries were looked up. Apart from a few cases, all relevant data could be collected. It is to be regretted, that despite of all efforts, the author was unable to localize Dreyer's estate (which might have been considerable).
Other subjects of this study are the development of telescopes and observing methods as well as the scientific status of observatories and astronomers. Most interesting is their communication, often enriched with mutual criticism. Controversial discussions arose particularly on identification, cataloguing and description (drawing) of nebulae; the letter being a very subjective issue. Central were the problems of existence, resolution, structure and variability. Different site conditions, apertures and the observers abilities to perceive and sketch an object, clearly demonstrate the limitations of visual observing. Disputed cases are the Orion nebula, the spiral galaxy M 51 in Canes Venatici, the Merope nebula in the Pleiades and Hind's Variable Nebula in Taurus. These stories of these popular objects are presented in detail.
The work provides a comprehensive review about the problems and achievements in the study of nebulae and clusters during the 19th century. It particularly shows, how strong the issue was still confined in the narrow scheme of classic position astronomy, thus inhibiting major progress. Only a few persons, among them both Herschel and Lamont, took time reflecting about the physical condition of the non-stellar objects. But visual observations could give no more than a mere qualitative (and thus assailable) picture. Due to the lack of knowledge, substantial results had to wait for the new astrophysical methods. Fortunately the large number of catalogued nebulae offered a sufficient sample for such advanced studies.
Finally the further development is treated in this work. Concerning the NGC, this yielded many corrections and supplements: starting with Dreyer's Index Catalogues, published in 1895 and 1908, till modern revisions of various quality. The appendix presents data for over 200 telescopes as well as extensive indices on literature, persons, sites and objects.
Table of Content
2 William Herschel's Catalogues
3 John Herschel's Slough Observations
4 Discoveries Made in Parallel to John Herschel's Slough Observations
5 John Herschel at the Cape of Good Hope
6 The Time After Herschel's Observations Till Auwers' List of New Nebulae
7 Compilation of the General Catalogue
8 Dreyer's First Catalogue: the Supplement to Herschel's General Catalogue
9 Compilation of the New General Catalogue
10 The New General Catalogue: Publication, Analysis, and Impact
11 Special Themes
- Position Measurements of Nebulae
- Nebula Drawings: Facts or Fiction?
- M 51 and the Spiral Structure
- Hind's Variable Nebula (NGC 1555) and Its Vicinity
- D'Arrest, Dreyer and the Variable Nebulae
- Pleiades Nebulae
- Telescope Data
- Literature, Internet Sources
- Index of Persons
- Index of Sites
- Index of Figured Objects