The Role of Images in Astronomical Discovery
Page 36
galaxies look very similar in the two very different wavelength regimes. Drastic differences
are found only for the most dusty galaxies.” The advantage of infrared imaging is that it is
less prone to the “hiding” effect of obscuring dust, an issue that Heber Curtis had already
addressed in 1918 (Chapter 3).
And what about the Galaxy Zoo project? This is a citizen science project that was started
in order to classify the millions of galaxies imaged by the Sloan Digital Sky Survey.56
Classifying this multitude of objects by the naked eye appeared impossible. There is no
computer algorithm that can reproduce the human ability to tell galaxy classes apart. Also,
powerful new telescopes and techniques have enabled galaxies to be observed further back
in time. Very deep images reveal a world of galaxies, which seems different from those in
54 M. J. S. Rudwick, The Emergence of a Visual Language for Geological Science 1760–1840, History of Science, 1976, Vol. XIV, pp. 149–195.
55 R. Buta et al. present a detailed discussion of recent developments in galaxy classification in the introductory part of The de Vaucouleurs Atlas of Galaxies, op. cit., pp. 27–80.
56 To learn more on the Galaxy Zoo project and the Sloan Digital Sky Survey, see www.galaxyzoo.org and www.sdss.com.
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Part III – Organizing the World of Galaxies
the nearby universe, even taking into account the reduced spatial resolution on the objects.
Despite present obstacles, it is clear that large data sets and artificial-intelligence tools will
advance galaxy classification in ways we cannot predict.
It is important to reiterate that galaxy classification systems are empirical; they are not
based on theory. Nevertheless, enormous effort has been devoted to linking the shapes of
galaxies to the physical processes taking place through the aeons of galaxy history.57 Allan
Sandage has summarized some key points for understanding how galaxies appear to us:
“The difference in time variation of the star formation rate for galaxies of different Hubble
type seems capable of explaining the five principal facts of observation concerning the
Hubble sequence. These are (1) the bulge-to-disk ratio is a function of Hubble type, (2) the
disk surface brightness varies systematically along the sequence, (3) the integrated colour
also changes progressively as a monotone function of the type, (4) the mean age of the disk
also varies in the same progression, and (5) the present star formation rate per unit mass for
Sc galaxies is much larger than for S0 and Sa galaxies.”58
What is astonishing is how successful morphology has been as a classification criterion.
In his book on the topic of discovery and classification, the American astronomer Steven
Dick commented that it was remarkable that galaxy classification systems proved to be as
good as they were, given the difficulties in correlating galaxy morphology with physical
significance.59 The simple property of galaxy shape is what runs through all the atlases
I have presented and discussed. Now as we probe the distant universe and try to classify
young galaxies, it is astonishing that we are using the simple criteria developed in the 1920s
by Reynolds, Lundmark and Hubble. Halton Arp would be very pleased by the multitude
of “peculiar” objects observed in the young universe . . . Galaxy atlases have been an out-
standing manifestation of the power of images within scientific discovery. Let us see how
they have been used.
57 Recent development in galaxy classification includes theoretical aspects and insights. See R. Buta, Galaxy Morphology, in Secular Evolution of Galaxies, J. Falcón-Barroso and J. H. Knapen (editors), Cambridge: Cambridge University Press, 2013, pp. 155–258.
58 A. R. Sandage, Star Formation Rates, Galaxy Morphology, and the Hubble Sequence, Astronomy & Astrophysics, 1986, Vol. 16, pp. 89–101 (quote from p. 89).
59 S. J. Dick, Discovery and Classification in Astronomy, Controversy and Consensus, Cambridge: Cambridge University press, 2013, p. 260.
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11
Atlases of Galaxies, Viewed by Their Users
The atlases drill the eye of the beginner and refresh the eye of the old
hand.
Lorraine Daston and Peter Galison 1
An artistic achievement, this volume is also a scholarly work of major
proportions.
George Field 2
For amateurs, this is a marvelous photographic atlas that includes almost
all the galaxies they usually look at.
Walter Scott Houston 3
Who Have Used Galaxy Atlases and What Have They Used Them For?
The atlases of galaxies published during the last 60 years or so have been scholarly cre-
ations. They have reflected our rapidly increasing knowledge and understanding of galax-
ies. These special publications were also driven by progress in our ability to image the sky
with larger, more powerful telescopes and cameras of increasing sensitivity and larger fields
of view. It is well worth quoting again Daston and Galison: “Not only do images make the
atlas; atlas images make the science.” Atlases are the repositories of recorded images for
the observational sciences. Let us explore the following question: beyond being displays
and repositories of current knowledge, do they also generate new knowledge?
Scientific atlases are considered to be specialized products, aimed at the experts. Hence,
galaxy atlases were produced primarily to fulfil specific needs of researchers in the disci-
pline, and to inform the practitioners in adjacent research fields. Nonetheless, a few of the
galaxy atlases discussed in the previous chapter (and in the appendix) have reached a wider
audience. Astronomy is not that exclusive a discipline. Like ornithology, entomology and
other natural sciences, it sustains cohorts of amateur astronomers around the world. Many
1 L. Daston and P. Galison, Objectivity, New York: Zone Books, 2007, p. 23.
2 G. Field, Book Review: The Hubble Atlas of Galaxies, American Scientist, 1962, Vol. 50, p. 212A.
3 S. H. Walter, Book Review: Atlas of Galaxies Useful for Measuring the Cosmological Distance Scale, Sky and Telescope, 1989, Vol. 78, p. 40.
233
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Part III – Organizing the World of Galaxies
of them are curious and inquisitive, and several are skillful astrophotographers. Over the
years, passionate aficionados have equipped themselves with the latest technology to make
their telescopes and imagers more powerful, to satisfy their quest for more knowledge.
With their ability to observe and photograph thousands of galaxies, even with relatively
small telescopes, amateur astronomers have been keen users of galaxy atlases.
This increasing audience for fine astronomical images and atlases has resulted in the
recent publication of a few atlases aimed at a wider readership.4 For the dedicated amateur,
Jeff Kanipe and Dennis Webb, with a team of amateur astronomers, have put together the
unique The Arp Atlas of Peculiar Galaxies.5 For the general public, a fine example is Chris-
tensen et al.’s Cosmic Collisions: The Hubble Atlas of Merging Galaxies.6 And Wray’s The
Color Atlas of Galaxies and, more recently, The Multiwavelength Atlas of Galaxies by
Glen
Mackie (see appendix) have a strong pedagogical approach.7
Several scientific atlases have been used for purposes beyond the original intent of their
designers and authors. This has been in great part due to the high quality of the publications
and to the beauty of the images presented in these works. Some of the galaxy atlases proved
to be no exception to this broader usage. By carefully browsing through The Hubble Atlas
of Galaxies, even a newcomer can quickly learn about the major classes of galaxies and
recognize the basic morphologies, after a brief initiation. Ultimately, the majority of the
galaxy atlases are pleasing to the eye and rewarding for the inquisitive mind; the fact that
the images are black-and-white reproductions has not diminished the aesthetic value of the
books. Finally, in the fine tradition of atlases, size counts. The designers and producers of
galaxy atlases took care to include several full-page reproductions of good quality, some
awe-inspiring.
Consequently, atlases have served for training and teaching, and to initiate the neophyte
researcher. In teaching, atlases have been used to define the standards of how galaxies are to
be seen and depicted. Teachers have used the objects illustrated to select a galaxy or a set of
galaxies they wish to present to students of an astronomy course; or to highlight a distinct
category of objects or a single object that deviates from the “standards” of the atlases; or
even point out objects (e.g. “peculiar” galaxies) that are blatantly omitted from the atlas.
Canadian astronomer Marshall McCall writes: “I have used The Hubble Atlas of Galaxies
in pretty much every course I teach, because it is a foundation for classifications. However,
I use it to illustrate the Revised Hubble System of de Vaucouleurs, not the Hubble System
of Sandage. Another book I use for teaching is this giant Atlas of Galaxies produced by
NASA.”8 On many occasions, atlases have been the source of material to define a sample
of objects for a thesis project and to initiate a new research program.
4 Not an atlas, but a highly popular large book of galaxy images, is T. Ferris’s Galaxies, New York: Random House Publishing, 1988.
5 J. Kanipe and D. Webb, The Arp Atlas of Peculiar Galaxies, A Chronicle and Observer’s Guide, Richmond: Willman Bell, Inc., 2006.
6 L. L. Christensen, D. de Martin and R. Y. Shida, Cosmic Collisions: The Hubble Atlas of Merging Galaxies, New York: Springer, 2009.
7 J. Wray, Color Atlas of Galaxies, Cambridge: Cambridge University Press, 1988; G. Mackie, The Multiwavelength Atlas of Galaxies, Cambridge: Cambridge University Press, 2011.
8 E-mail exchange with the author.
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11. Atlases of Galaxies, Viewed by Their Users
235
Citations of Atlases and Their Usage
An accepted measure of the use, success and importance of a scientific work is the cumula-
tive number of citations it has received over the years, especially in the specialized articles
published. There may be various reasons for citing a galaxy atlas: authors may simply wish
to refer to an image in the atlas or give a description of a chosen sample of galaxies for
observing or study; they may be comparing an object with the archetypes in the atlases; or
they may also be discussing classification schemes, with respect to their success, limitation
or failure.
Table 11.1 lists the galaxy atlases covered in this book, with the year in which they
appeared. The successive columns indicate whether photometric information (isophotal
maps, radial brightness profiles) is included; the type of audience that the atlas was mainly
aimed to reach, or has reached (research, training or public); the number of citations (from
SAO/NASA Astrophysics Data System) up to the beginning of 2017; and the number of
book reviews is given in the last column.
In the fields of astronomy and astrophysics, and the physical sciences in general, books
(including atlases) are not cited as systematically as research articles in peer-reviewed jour-
nals. Their relative importance for citation is less than that in the humanities or social sci-
ences. This is not because books are of lesser importance but reflects a cultural habit within
the natural sciences’ research communities. Here, books are thought to be compendia or
summaries of the research published in the scholarly journals, hence used in teaching or
researching fundamentals, e.g. in exploring a new avenue of research or for the better under-
standing of a problem being addressed. The original articles in the professional journals are
cited in preference because they contain more details, have the fully listed authorship and
institutional affiliations, and enjoy the prestige of the journal that published them. There-
fore, in terms of citations, atlases may be regarded more as books than original research
articles.
Since the majority of the galaxy atlases were published some time ago, the number of
citations is still a meaningful measure of their impact, especially for those that were pub-
lished before 2000. It is noticeable that Sérsic’s Atlas de galaxias australes, published in
the Spanish language and not a particularly flamboyant publication, had about 1,340 cita-
tions at the beginning of 2017; it is, together with Sandage’s The Hubble Atlas of Galaxies
(1,263 citations) the most cited atlas of galaxies, followed by Arp’s Atlas of Peculiar Galax-
ies (1,141 citations). The popularity of Sérsic’s work is very likely due to its inclusion of
photometric maps and data. However, the RSA mini-atlas/catalogue had the greatest number
of citations, 1,587.
Moreover, as it is well known that atlases of galaxies reach beyond the specialists, it
is a reasonable to assume that they have been used several times this number of citations.
Whilst being a quantitative measure the actual number of citations does not necessarily
give the full intellectual impact of a published work. For example, it is impossible to mea-
sure the educational input on a young kid who happens to open the pages of an atlas and
“gets hooked” by the images while visiting a friend. And how many Ph.D. students were
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Table 11.1 Atlases of galaxies, book reviews and citations
Book
Atlas title
Authors
Year
Isophotes B&w/colour
Research Training Public Citations reviews
“A Survey of the External Galaxies
Shapley and Ames 1932
No
Catalog only
✔
64
0
Brighter Than the Thirteenth
Magnitude”
The Hubble Atlas of Galaxies
Sandage
1961
No
B&W
✔
✔
✔
1,263
4
Atlas of Peculiar Galaxies
Arp
1966
No
B&W
✔
✔
1,141
0
Atlas de galaxias australes
Sérsic
1968
Yes
B&W
✔
✔
1,340
1<
br />
An Atlas of 21 cm HI Line Profiles of 61
Rots
1979
Yes
Profiles, maps
✔
5
Galaxies
The Revised Shapley–Ames Catalog of
Sandage and
1981, No
B&W
✔
✔
1,587
3
Bright Galaxies
Tammann
1987
An Atlas of Selected Galaxies
Takase, Kodaira
1984
Yes
B&W
✔
14
and Okamura
Color Atlas of Galaxies
Wray
1988
No
Colour
✔
✔
✔
67
4
Atlas of Galaxies Useful for Measuring
Sandage and
1988
No
B&W
✔
✔
139
4
the Cosmological Distance Scale
Bedke
.013
Photometric Atlas of Northern Bright
Kodaira, Okamura
1990
Yes
B&W
✔
42
Galaxies
and Ichikawa
Atlas of Compact Groups of Galaxies
Hickson
1993
?
B&W – CCD
✔
✔
109
7
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imaging
The Carnegie Atlas of Galaxies
Sandage and
1994
No
B&W
✔
✔
✔
310
4
, subject to the Cambridge Core
Bedke
The de Vaucouleurs Atlas of Galaxies
Buta, Corwin and
2007
No
B&W – CCD
✔
✔
60
3
Odewahn
imaging
11. Atlases of Galaxies, Viewed by Their Users
237
re-oriented in their research by flipping through the pages of one of these great galaxy
atlases? This is an impact we learn only by interviewing active researchers.
Inspiring Atlases
As has been mentioned several times already, the impact of Sandage’s The Hubble Atlas of
Galaxies has been huge; it has inspired many young researchers. Together with the Atlas