Stars, Peripheral Scientists, and Equations: The Case of M. N. Saha Deepanwita Dasgupta* Peripheral actors rarely make an appearance in the general story of scientific practice, and their work in science is usually viewed as somewhat derivative of the practices of the main community. Contrary to this received model, here I argue that the peripheral contexts of science can be quite important and reveal novel conduits to creative scientific thinking. Not only can such contexts offer us a new window into how contributory expertise in science could be born amid difficult circumstances, they also allow us to see how new scientific communities could be founded during such encounters. Using case studies of M. N. Saha and other physicists in early twentieth-century India, I argue that such modest practices begin when peripheral protagonists seek to initiate new trading zones with the established centers of science. The resulting exchanges can give rise to new breakthroughs and conceptual changes in scientific practice. Such peripheral breakthroughs can be studied cognitively, giving us newer models of scientific practice as well as creating a new kind of self-image for such scientists. Key words: M. N. Saha; trading zones; ionization; Saha equation; peripheral science. ‘‘Of necessity one has to begin by following the simplest path.’’ 1 —Fred Hoyle, ‘‘Motives and Aims of the Scientist’’ The Multiple Contexts of Scientific Practice In the decades following the publication of Thomas Kuhn’s The Structure of Sci- entific Revolutions, significant scholarly attention has focused on the different origins and contexts of scientific knowledge. Sociologists and historians have ex- amined how scientific claims have been evaluated and received in different cultures and in different disciplinary contexts. 2 Yet in spite of this close attention to the diversity of science, a rather important question about scientific practice has so far attracted little attention from either historians or philosophers of science. This is the question of how one enters a scientific practice and how one comes to acquire contributory expertise in it. What are the different pathways by which one * Deepanwita Dasgupta is a philosopher of science in the Department of Philosophy, East Tennessee State University. Phys. Perspect. 17 (2015) 83–106 Ó 2015 Springer Basel 1422-6944/15/020083-24 DOI 10.1007/s00016-015-0159-7 Physics in Perspective 83