The Sun a Star, and Every Star a Sun

7 December 2016


The Thomas Digges chart of a Copernican solar system from 1576.

The Thomas Digges chart of a Copernican solar system from 1576.

The full awareness of our sun being a star, and the stars being suns in their own right, was a development nearly coextensive with the entire history of science, from its earliest stirrings in ancient Greece to its modern form at the present time. During the Enlightenment there was already a growing realization of this, as can be seen in a number of scientific works of the period, but scientific proof had to wait for a few generations more until new technologies made available by the industrial revolution produced scientific instruments equal to the task.


The scientific confirmation of this understanding of cosmology, which is, in a sense, the affirmation of Copernicanism (as distinct from heliocentrism) came with two scientific discoveries of the nineteenth century: the parallax of 61 Cygni, measured by Friedrich Wilhelm Bessel and published in 1838, which was the first accurate distance measured to a star other than the sun, and the spectroscopy work of several scientists — Fraunhofer, Bunsen, Kirchhoff, Huggins, and Secchi, inter alia (cf. Spectroscopy and the Birth of Astrophysics) — which demonstrated the precise chemical composition of the stars, and therefore showed them to be made of the same chemical elements found on Earth. The stars were no longer immeasurable or unknowable; they were now open to scientific study.

Joseph von Fraunhofer invented the spectroscope, and first observed what are now called Fraunhofer lines.

Joseph von Fraunhofer invented the spectroscope, and first observed what are now called Fraunhofer lines.

The Ptolemaic conception of the universe that preceded this Copernican conception painted a very different picture of the universe, and of the place of human beings within that universe. According to the Ptolemaic cosmology, the heavens were made of a different material than the Earth and its denizens (viz. quintessence — the fifth element, i.e., the element other than earth, air, fire, and water). Everything below the sphere of the moon — sublunary — was ephemeral and subject to decay. Everything beyond the sphere of the moon — superlunary — was imperishable and perfect. Astronomical bodies were perfectly spherical, and moved in perfectly circular lines (except for the epicycles). Comets were a problem (i.e., an anomaly), because their elliptical orbits ought to send them crashing through the perfect celestial spheres.

Geocentric Ptolemaic cosmology by Orance Fine (1494-1555)

Geocentric Ptolemaic cosmology by Orance Fine (1494-1555)

This Ptolemaic cosmology largely satisfied the scientific, philosophical, moral, and spiritual needs of western thought from classical antiquity to the end of the Middle Ages, and this satisfaction presumably follows from a deep consonance between this conception of the cosmos and a metaphysical vision of what the world ought to be. Ptolemaic cosmology is the intellectual fulfillment of a certain kind of heart’s desire. But this was not the only metaphysical vision of the world having its origins (or, at least, its initial expression) in classical antiquity. Another intellectual tradition that pointed in a different direction was mathematics.

The imaginative background of Ptolemaic cosmology; an image of God as architect from a Moralized Bible, folio 1 verso, Österreichische Nationalbibliothek, Vienna.

The imaginative background of Ptolemaic cosmology; an image of God as architect from a Moralized Bible, folio 1 verso, Österreichische Nationalbibliothek, Vienna.

Mathematics was the first science to attain anything like the rigor that we demand of science today. It remains an open question to this day — an open philosophical question — whether mathematics is a science, one of the sciences (a science among sciences), or whether it is something else entirely, which happens to be useful in the sciences, as, for example, the formal propaedeutic to the empirical sciences, in need of formal structure in order to organize their empirical content. The sciences, in fact, get their rigor from mathematics, so that if there were no mathematical rigor, there would be no possibility of scientific rigor.

Euclid provided the model of formal thought with his axiomatization of geometry. Legend has it that there was a sign over the door of Plato's Academy stating, 'Let no one enter here who has not studied geometry.'

Euclid provided the model of formal thought with his axiomatization of geometry. Legend has it that there was a sign over the door of Plato’s Academy stating, ‘Let no one enter here who has not studied geometry.’

Mathematics has been known since antiquity as the paradigm of exact thought, of precision, the model for all sciences to follow (remembering what science meant to the ancients, which is not what it means today: a demonstrative science based on first principles), and this precision has been seen as a function of its formalism, which is to say its definiteness, it boundedness, its participation in the peras. Despite this there was yet a recognition of the infinite (apeiron) in mathematics. I would go further, and assert that, while mathematics as a rigorous science has its origins in the peras, it has its telos in the apeiron. This is a dialectical development, as we will see below in Proclus.

An early copy of Euclid's Elements, which axiomatically systematized geometry.

An early copy of Euclid’s Elements, which axiomatically systematized geometry.

Proclus expresses the negative character of the infinite in his commentary on Euclid’s Elements:

“…the infinite is altogether incomprehensible to knowledge; rather it takes it hypothetically and uses only the finite for demonstration; that is, it assumes the infinite not for the sake of the infinite, but for the sake the infinite.”

Proclus, A Commentary on the First Book of Euclid’s Elements, translated, with an introduction and notes, by Glenn R. Morrow, Princeton: Princeton University Press, 1992, Propositions: Part One, XII, p. 223. This whole section is relevant, but I have quoted only a brief portion.

There is no question that the apeiron appeared on the inferior side of the Pythagorean table of opposites, but it is also interesting to note what Proclus says earlier on:

“The objects of Nous, by virtue of their inherent simplicity, are the first partakers of the Limit (περας) and the Unlimited (ἄπειρον). Their unity, their identity, and their stable and abiding existence they derive from the Limit; but for their variety, their generative fertility, and their divine otherness and progression they draw upon the Unlimited. Mathematicals are the offspring of the Limit and the Unlimited…”

Proclus, Commentary on the First Book of Euclid, Prologue: Part One, Chap. II

Here the apeiron appears on an equal footing with the peras, both being necessary to mathematical being. “Mathematicals” are born of the dialectic of the finite and the infinite. Both of these elements are also found (hundreds of years earlier) in the foundations of geometry. As the philosophers produced proofs that there could be no infinite number or infinite space, Euclid spoke of lines and planes extended “indefinitely” (as “apeiron” is usually translated in Euclid). Even later when the Stoics held that the material world was surrounded by an infinite void, this void had special properties which distinguished it from the material world, and indeed which kept the material world from having any relation with the void. The use of infinities in geometry, however, even though in an abstract context, force one to maintain that space locally, directly before one, is essentially of the same kind as space anywhere else along the infinite extent of a line, and indeed the same as space infinitely distant. All spaces are of the same kind, and all are related to each other. This constitutes a purely formal conception of the uniformity and continuity of nature. One might interpret the subsequent history of science as redeeming, through empirical evidence, this formal insight.


The infinite is the “internal horizon” (to use a Husserlian phrase) and the telos of mathematical objects. Given this conception of mathematics, the question that I find myself asking is this: what was the mathematical horizon of the Greeks? Did the idea of a line or a plane immediately suggest to them an infinite extension, and did the idea of number immediately suggest the infinite progression of the series, or were the Greeks able to contain these conceptions within the peras, using them not unlike we use them, but allowing them to remain limited? Did ancient mathematical imagination encompass the infinite, or must such a conception of mathematical objects (as embedded in the infinite) wait for the infinite to be disassociated from the apeiron?


The wait was not long. While the explicit formulation of the mathematical infinite had to wait until Cantor in the nineteenth century, Greek thought was dialectical, so regardless of the nature of mathematical concepts as initially conceived, these concepts inevitably passed into their opposite numbers and grew in depth and comprehensiveness as a result of the development of this dialectic. Greek thought may have begun with an intellectual commitment to the peras, and a desire to contain mathematics within the peras, consequently an almost ideological effort to avoid the mathematical infinite, but a commitment to dialectic confounds the demand for limitation. It is, then, this dialectical character of Greek thought that gives us the transition from purely local concepts to a formal concept of the uniformity of nature, and then the transition from a formal conception of uniformity to an empirical conception of uniformity, and this latter is the cosmological principle that is central to contemporary cosmology.

Geometry as represented by Raphael in The School of Athens.

Geometry as represented by Raphael in The School of Athens.

The cosmological principle brings us back to where we started: To say that the sun is a star, and every star a sun, is to say that the sun is a star among stars. Earth is a planet among planets. The Milky Way is a galaxy among galaxies. This is not only a Copernican idea, it is also a formal idea, like the formal conception of the uniformity of nature. (In A Being Among Beings I made a similar about biological beings.) To be one among others of the same kind is to be a member of a class, and to be a member of a class is to be the value of a variable. Quine, we recall, said that to be is to be the value of a variable. This is a highly abstract and formal conception of ontology, and that is precisely the importance of the formulation. This is the point beyond which we can begin to reason rigorously about our place in the universe.

The sun in its local stellar neighborhood as a star among stars.

The sun in its local stellar neighborhood as a star among stars.

We require a class of instances before we can draw inductive inferences, generalize from all members of this class, or formalize the concept represented by any individual member of that class. This is one of the formal presuppositions of scientific thought never made explicit in the methodology of science. We could not formulate the cosmological principle if we did not have a concept of “essentially the same,” because the “same” view that we see looking in any direction in the universe is not identically the same, but rather essentially the same. Of any two views of the universe, every detail is different, but the overview is the same. The cosmological principle is not a generalization, not an inductive inference from empirical evidence; it is a formal idea, a regulative idea that makes a certain kind of cosmological thought possible.


Formal principles like this are present throughout the sciences, though not often recognized for what they are. Bessel’s observations of 61 Cygni not only required industrialized technology to produce the appropriate scientific instruments, these observations also presupposed the mathematics originating in classical antiquity, so that the nineteenth century scientific work that proved the stars to be like our sun (and vice versa) was predicated upon parallel formal conceptions of universality structured into mathematical thought since its inception as a theoretical discipline (in contradistinction to the practical use of mathematics as a tool of engineering). Formal Copernicanism preceded empirical Copernicanism. Without that formal component of scientific knowledge, that scientific knowledge would never have come into being.

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One Response to “The Sun a Star, and Every Star a Sun”

  1. xcalibur said

    It’s true – details differ everywhere, but principles remain the same. This is an important axiom, but one that takes discipline to accept. I’ve noticed that it is part of human nature to assign the self (or in-group) a central role, while relegating everything else to the periphery. We can see this in psychology, in the pre-copernican view of earth at the center of the universe, in China referring to itself as the “Central Kingdom” as opposed to the “exotic far east”, Greeks vs barbarians, and so on. People everywhere have seen the world revolving around them, with everything outside of their sphere either considered inferior or assigned some fantastic imaginative form.

    It takes intellectual discipline to come to terms with the fact that one’s self is just one out of 7 billion+ humans, that one’s tribe/country/etc. is just one out of many, and that the same applies to our planet, sun, and galaxy. However, if we are going to reason about the world, it is important to embrace this axiom, and correct for the egocentric bias.

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