“Sunrise in Greece” is a previously unpublished article from Dr. Gordon H. Clark’s papers. It is presented to the public for the first time here on the Gordon H Clark Foundation website. Both the original scan of the document and a typed version for search ability are here presented. If you notice any typos on the typed document please email the administrator at email@example.com
**Items from the unpublished papers of Dr. Gordon H. Clark should not be considered his definitive statement on the particular topic addressed. These papers are being provided for educational value. For Dr. Clark’s official positions consult his published writings.**
Sunrise in Greece1
By Gordon H. Clark2
In antiquity the study of astronomy was motivated by a desire to answer four questions. And the progress of astronomical theory was directed by the attempt to make the four answers consistent.
The first question is: What makes day and night? To say that the sun revolves about the earth in a regular period of twenty-four hours is simple enough. But a second question complicates the situation. Why do the stars return to their position in less than twenty-four hours? Of course they may revolve in complete independence of the sun in a shorter time. Complete independence, however, is the least desirable hypothesis. A third question is: Why do not the planets and the sun return to their positions as the stars do? And, lastly, why does not the sun rise at the same place everyday?
It is to be observed that these questions are simple and obvious to nearly anyone. Their answers, however, are not so quickly forthcoming.
In Greek philosophy the first to answer these questions was Anaximander, who lived and wrote about 550 B.C. His theory posits a vortex about the earth as a center. The earth itself rotates slowly and the heavenly bodies revolve quickly. That the heavenly bodies are conceived as rings of fire, hidden from view except at one aperture, does not affect the general result for astronomy. It is rather to be noted that the earth is at the center of the system and that it rotates. This combination, necessary in a vortex theory, is somewhat peculiar in antiquity since those philosophers who made the earth move, generally denied that it was at the center, and those who insisted that it was at the center ordinarily denied it motion.
There are at least two objections which rendered the vortex theory unsatisfactory. In the first place, it does not well explain the regular retrogressions of the planets. To be sure, the universal fluid may contain eddies which affect only the planets, but this is a complication which if possible should be avoided in the interests of simplicity. A second difficulty was Anaximander’s own discovery of the obliquity of the ecliptic. If you should stir vigorously the tea and tea leaves in your cup, you would soon discover how difficult it is to get some leaves revolving on a plane inclined 23º to the plane of the other orbits. But although the discovery of this obliquity is attributed to Anaximander, our fragments give us no evidence that he changed his vortex theory to accommodate his discovery.
The next important development in astronomy was made by the Pythagoreans. They assumed that the earth revolved about a central fire. This central fire was not the sun, for the sun, like the earth and other planets, also revolved about the central fire and reflected its light. To explain why we on earth never see the central fire, they assumed the equality of the earth’s periods of rotation and anti-rotation. Night and day, then, could be explained by the much greater velocity of the sun, though as a matter of fact Aristotle reports that night and day are accounted for by the earth’s revolution about the central fire. The awkwardness of Aristotle’s expression here must be attributed either to incomplete statement, to a mistake, to differences within the Pythagorean school, or to the inaccuracy of other source materials. The central fire theory, however, allows an explanation of the greater frequency of lunar eclipses over solar eclipses by assuming between the fire and the earth other unseen bodies which could cast a shadow on the moon but not on the more distant sun. This theory also saves the motion of the moon, simply by giving it a lesser velocity than that of the sun; but the retrogression of the planets, that is, the fact that sometimes they travel faster and sometimes slower than the sun, receives no explanation. The obliquity of the ecliptic may not be made impossible on this scheme, but there is no apparent simplicity possible. And simplicity is highly desirable. In fact, so highly desirable that the problem of ancient astronomy can be formulated as follows: What circular and perfectly regular motions must one assume to save the planetary appearances? This formulation of the problem is so eloquent that it could be expected only after considerable reflection on astronomical phenomena. It is therefore necessary next to turn to Plato who both offered several theories himself and who also stimulated speculation on the part of capable students.
Now the interpretation of Plato is difficult because when he was not certain of his theories, he often put them in the form of myth. The astronomical myth in the Phaedo is so vague that virtually the only conclusion to be drawn from it is that Plato was dissatisfied with previous theories. Apparently referring to previous attempts to use the diameter of the earth as the astronomical unit, he writes: “The earth is itself neither in size nor in other respects such as it is supposed to be by those who habitually discourse about it.”3 He does, however, place his stamp of approval on Anaximander’s locating the earth at the center and on the reason for the earth’s remaining there: “If the earth is round and in the middle of the heavens, it needs neither air nor any other force to keep it from falling… for a body which is in equipoise and is placed in the center of something homogeneous cannot change its inclination in any direction.”4 More than this in the way of positive astronomical statement the myth does not supply.
Some years later, Plato appends another myth to the Republic in which he ventures a little further. A straight pillar of light is stretched across the whole heaven and earth. Its extremities are fastened by chains to the sky, and this light binds the sky together. What Plato means by the pillar of light is not certain; but in spite of its being pulled straight the most plausible suggestion is that it represents the Milky Way. Although difficulties of interpretation remain, it may be thought that the observer is completely outside the universe looking down in the plane of the Milky Way and, therefore, seeing it only as a straight line.
1 Read before ΣΠΣ, Honorary Physics Society, May 19th, 1937.
2 Transcribed and edited by Hiram R. Diaz III. Editorial changes are explained in the Editorial Appendix (p.8).
3 Phaedo, 108c.
4 Phaedo, 109a.