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Heliocentric tangents

SIR -- The heliocentric hypothesis, so able championed by
Copernicus and Galileo(1), is authoritatively said to have
originated with Aristarchus of Samos in the third century BC. 
Sand-Reckoner, written by Aristarchus's younger contemporary
Archimedes before 216 BC(2), attributed to Aristarchus a book
containing the hypotheses "that the fixed stars and the sun remain
unmoved, [and] that the earth revolves about the sun in the
circumference of a circle, the sun lying in the middle of the
orbit...".  Aristarchus's (lost) book is thought to have
"clearly...also included some kind of geometrical proof"(3).  
Aristarchus had also produced a treatise On the sizes and distances
of the Sun and Moon, which has survived intact.  Its "excellent"
methodology confirms that Aristarchus's (probably later)
heliocentric hypothesis was similarly "not irresponsible" but
rather the work of a conscientious astronomer"(2).
  Nicholas Copernicus's De Revolutionibus (1543) acknowledged
Aristarchus but not his heliocentric hypothesis(4); however, it
seems certain that Copernicus was also acquainted with the latter. 
For example, his original manuscript had referred to the opinion of
Aristarchus on the movement of the Earth, but this reference was
subsequently "suppressed" or "scored out"(4).  Moreover, in
relating the views of Philolaus, Heracleides and Ecphantus on the
question of movement of the Earth, Copernicus's Preface quoted from
De Placitis Philosophorum of pseudo-Plutarch, a work in which may
also be found: "Aristarchus places the Sun among the fixed stars,
and holds that the EArth moves around the Sun's circle"(4).  And De
Revolutionibus (IV, 32) cites Archimedes' Measurement of the
Circle, a treatise commonly found in the company of Sand-
Reckoner(5).
  Copernicus's unquestionably pivotal contribution to astronomy was
his grand revival of the heliocentric hypothesis as a systematic
planetary theory(4).  But in order to fit theory to observation,
Copernicus had retained the geometric devices used by Ptolemy (the
deferent, epicycle and excentric), and had referred details of
planetary movements not to the Sun but rather to the centre of the
Earth's orbit.  Because of technical and other difficulties with
the copernican system, the astronomer Tycho Brahe (1546-1601)
rejected it.  Brahe had compiled an unrivalled set of observations,
which he thought would demonstrate that the Sun and Moon travel
around the Earth while the other planets travel round the Sun(6). 
 After Brahe's death, Johannes Kepler (1571-1630) invested years in
the analysis of Brahe's data, culminating in the derivation of
Kepler's three laws of planetary motion.  These provided a precise
and enduring mathematical characterization of the heliocentric
hypothesis, thus serving to support the position of Copernicus
while ironically refuting that of Brahe.

STUART HALE SHAKMAN

1. Nature 337, 101 (1989).
2. Sarton, G. A History of Science: Hellenistic Science and Culture
in the Last Three Centuries BC, 54-57 (Harvard University,
Cambridge, 1959).
3. Heath, T. Aristarchus of Samos, 301-302 (Clarendon, Oxford,
1913).
4. Armitage, A. Copernicus (Allen & Unwin, London, 1938).
5. Heath, T., The Works of Archimedes xxiv-xxvi (Dover, N.Y.,
1912).
6. Armitage, A. Sun Thou Stand Still 149, 169-175 (Sigma, London,
1947).