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In this Section, I discuss the contexts into which Galaxy Zoo emerged, describing the major challenge that the project set out to address and explaining why this challenge was so critical for cosmology (the subdiscipline of astronomy concerned with the origin, evolution and the ultimate face of the universe and in which Galaxy Zoo is located) as a whole. I first present an overview of the history of astronomy, explaining how cosmology has had a lowlier status than other astronomical subdisciplines because statistical confirmation of most of its basic conjectures has been lacking and how cosmologists therefore have been concerned with raising the status of cosmology. This has driven the development of methods over the past fifty years to gather much greater quantities of cosmological data (in this case, images of galaxies) to provide a firmer empirical foundation for cosmological theory. I will explain how the two approaches that had been available for processing this data (professional astronomers classifying the images by hand, and automated image recognition software) have so far been inadequate for the task: thus, the challenge facing cosmologists was the question of how to handle this data deluge. This leads into the subsequent Section, where I will describe how a team of cosmologists at the University of Oxford set out to respond to this challenge through the development of Galaxy Zoo.

4.2.1 Cosmology and the history of astronomy

Cosmology is a subdiscipline of astronomy, a discipline that sets out to answer questions that have fascinated people for millennia. Public, financial and material support for the study of the universe has relied on a number of different factors over time. The cosmos was an object of study for the Ancient Greeks, and was strongly related to their religious practices, and transcendental reasons have usually underpinned subsequent public and institutional support for the study of the universe (Bowler & Morus 2005). For instance, in the Middle Ages, the Catholic Church supported the study of the planets and stars as holding the key to unlocking some of the mysteries of God’s creation (although the study of the solar system was repressed during and after the life of Nicholas Copernicus after he suggested that the Earth, and thus Man, was not at the centre of the universe). In more recent decades, despite a decline in belief in organized religions in western society, there has been a strong continuation of support of the study of astronomy as humans seek to understand their place in the universe (Smith et al. 2010). Astronomy has also received support for more political or utilitarian reasons, such as its usefulness to navigation (Portolano 2000), military applications (Devorkin 1980) or practical spin-offs from the space programme (Goldin 2004). It has also played an important role in nation-building, and in international relations: projects such as building observatories or the space race provide a great deal of symbolism and status for nations. For instance,

71 Portolano (2000) describes how the building of an observatory in the early United States was presented as an opportunity for the USA to raise its status compared with European nations. In order to study these various questions of interest, a number of subdisciplines of astronomy developed over time, each studying different regions of the universe, or different objects in space. Along with cosmology, these sub-disciplines include: solar astronomy (the study of the Sun), planetary astronomy (planets in our Solar System), lunar astronomy (the Moon), and stellar astronomy (which studies the life cycle and properties of stars).

During much of the twentieth century, the central question cosmology sought to answer was whether the universe was steady-state (in the sense that it had no origin, no end-point and remained the same size throughout time) or did it originate with a Big Bang and, if so, will it continue to expand forever or will it begin to contract (and thus end in a Big Crunch)? In the closing decades of the twentieth century, the scientific consensus has come down firmly against the steady-state theory and in favour of the Big Bang. However, a number of major questions of interest remain unanswered, for instance relating to the underlying structure of the universe and the rate at which it is expanding and at what point it might begin to contract.

The astronomer Edwin Hubble, in the 1920s, established that the key to answering the questions about the universe lay in understanding the evolution and structure of galaxies (Hubble 1926). Hubble devised a classification scheme for galaxies, and this has underpinned work on galaxy morphology since. In this scheme, galaxies are classified according first to whether they were elliptical or spiral galaxies. In the case of elliptical galaxies, they were then further divided depending on whether they appeared circular or more elliptical in the sky. Spiral galaxies are classified according to how tightly their spiral arms are woven around their centre, and also whether (and how large) is a bulge at the centre of the galaxy. This classification scheme is known as ‘Hubble’s tuning fork’ (Figure 4.1).

4.2.2 The lowlier status of cosmology in astronomy

Answering these questions in the terms laid down by Hubble, however, has not been a straightforward task. The result of this is that compared with other sub-disciplines of astronomy, cosmology has often been regarded as having a somewhat lowlier status: for most of the twentieth century, cosmologists were not able to provide solid quantitative evidence to support its assertions and conjectures.

A major feature of the professionalization of science in general at the start of the twentieth century was a greater focus on mathematical methods (Porter 1996), and astronomy was no different, as it helped professional astronomers to differentiate themselves from the mass of amateurs. One reason is that quantitative methods helped

72 to endow their science with a greater sense of objectivity. Another was that it was a form of discourse available only to those who had received mathematical training as part of a university education, and thus served to exclude amateurs from contributing (Lankford 1981). Cosmologists’ struggles to deal in such terms mean that their field, in turn, struggled to attain the same status as other sub-disciplines of astronomy: for instance, one leading astronomer dismissed cosmology thus: ‘there are only two and a half facts in cosmology’, implying that the rest is merely speculative (quoted in Kragh (1996, p. 320). See also Bowler & Morus (2005)).

Figure 4.1: Hubble’s Tuning Fork. Hubble classified galaxies according to whether they were elliptical in shape (E0 through to E7, with the galaxy getting flatter in shape moving from left to right), spiral with a bar through the centre (SBa, SBb and SBc), or spiral without a bar (Sa, Sb and Sc). Hubble’s classification diagram

takes the shape of a tuning fork because he believed that galaxies evolved over time, from left (E0) to right (Sc or SBc): this is now known to be false. (Image taken from Sloan Digital Sky Survey website,

http://skyserver.sdss.org/dr1/en/proj/advanced/galaxies/tuningfork.asp (accessed: 28 November 2011)).

Throughout most of the 20th _{century, cosmology was hampered because there were insufficient records} of individual galaxies to provide robust statistical evidence for its conjectures. Sky surveys, which record the existence of astronomical phenomena, had been conducted since the late 1700s, but even by the mid-to-late twentieth century, the most advanced surveys comprised only thousands of images which were not of a high enough quality to detect the physical features of galaxies necessary for classification, and simply not of a scale to provide answers to cosmological conjectures to a high degree of statistical certainty. Furthermore, because they were expensive for research institutions to procure, many scientists hoping to conduct analysis found them difficult to access, thus slowing down research (Finkbeiner 2010).

73 In the 1980s, new methods of telescopy were developed which promised the opportunity for sky surveys to expand far beyond thousands of images, to produce images of much higher resolution, and to make them more readily available to researchers. Cosmologists saw this as offering the prospect for providing robust quantitative evidence to support their work (National Research Council 1991), and thus of raising the professional status of their sub-discipline relative to other astronomical sub-disciplines.

One such sky survey was the Sloan Digital Sky Survey (SDSS) (Gunn et al. 2006). In 2000, it began operation at the Apache Point Observatory in New Mexico, and recorded spectra for over one million objects. However, despite the public release of the SDSS data, one major barrier remained: how to proceed with the task of classifying such a large number of images.

Prior to Galaxy Zoo, the two alternatives for classifying galaxies were: 1) classifications by professional astronomers; and 2) automated image recognition. However, both of these approaches were found to be lacking in crucial respects as methods for classifying the images produced by the SDSS.

In the case of classifications by professional astronomers, this is a very time-consuming approach. Thus, catalogues of classifications by this method usually number thousands or tens of thousands of galaxies (for instance, see de Vaucouleurs et al. 1991; Schawinski et al. 2007). A sample of galaxies of this size is not large enough to provide sufficiently robust statistical confirmation of theories about galaxy morphology.

By contrast, the idea behind automated image recognition is that algorithms could classify a very large volume of galaxies in a short timescale. However, developers of algorithms have struggled to devise methods that can accurately classify galaxies in the terms set out in Hubble’s tuning fork. The methods devised as of 2007 were deficient in a number of ways: some were heavily dependent on the quality, colour and size of the image used (requiring better quality images that have been produced by sky surveys to date), some were too computationally- intensive , whilst others relied on proxies being used for galaxy classes (e.g. an algorithm classifying spirals and ellipticals according to whether they are blue or red, which results in many spirals being classified as ellipticals and vice versa). Finally, other algorithms have been devised that are more reliable at classification, but they sort according to criteria such as ‘asymmetry’, ‘clumpiness’ and ‘concentration’ (Conselice 2006, p. 1390), and thus have not been able to provide results that are comprehensible in terms of Hubble’s tuning fork, in turn meaning the results of these algorithms are not able to provide statistical evidence for or against proposed cosmological theories (Fortson et al. 2011).

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