Cleomedes was a Greek astronomer who wrote an influential work: On the Circular Motions of the Celestial Bodies.
Mathematical Profile (Excerpt):
- We should first discuss the perplexing question of the period in which Cleomedes lived.
- It is hard to estimate from these words how long after Posidonius the author, Cleomedes, is writing.
- Neugebauer, however, disagrees with these conclusions of Heath and proposes that Cleomedes wrote his text around 370 AD.
- His argument is based on a comment by Cleomedes in the text where he remarks than there are two bright stars (Aldebaran and Antares) such that the rising of one and the setting of the other take place at the same time.
- These stars Cleomedes claims lie at 15° of their sign.
- Using Ptolemy's positions for the stars at the time the Almagest Ⓣ(The major thesis: from the Arabic 'al-majisti' -- the Arabic translation of the Greek 'Mathematike Syntaxis' later translated into Latin as 'Magna Syntaxis') was written and Ptolemy's value of 1° per 100 years for precession, Neugebauer gets his date of 371 AD for Cleomedes writings, to which Neugebauer estimates a maximum error of 50 years on either side.
- Firstly the data in "On the Circular Motions of the Celestial Bodies" does not seem to be due to Cleomedes but to a variety of sources.
- Of course accepting this argument would make Cleomedes dates later still.
- Secondly the data in Cleomedes is of widely differing degrees of accuracy.
- Heath's comment that Cleomedes knows nothing of the works of Ptolemy is also less certain than it might at first appear.
- Cleomedes is writing an elementary textbook and it is certainly not always the case that one mentions recent research in a low level textbook.
- Not least of these is the fact that this was a period when many second rate textbooks of this nature were written and the style is not unlike that of other fourth century AD texts, some of which give the same astronomical data as Cleomedes.
- But this is not Cleomedes' main aim in writing the text.
- Cleomedes spends much time in his text showing that this is false, but it does seem as if he is going to extremes when he compares Epicureans unfavourably with rats, reptiles and worms.
- Cleomedes' own philosophical views show that he is a Stoic.
- Whenever a piece of text is thought to be due to Cleomedes himself, there is much evidence that his understanding of the topic was very limited and, but for the quality of his sources, one feels that Cleomedes would not fare any better than the Epicureans for naiveté.
- Lunar eclipses are described well in the text, and the conical shape of the earth's shadow shows an interesting depth of understanding (at least of Cleomedes' source).
- One further interest in Cleomedes' work is that it is in On the Circular Motions of the Celestial Bodies that we learn of Eratosthenes method of measuring the circumference of the earth.
- This is one of the best known of the achievements of early mathematical astronomy and we are indebted to Cleomedes for relating the method.
- Finally we should remark that Neugebauer suggests from a study of certain astronomical data given in On the Circular Motions of the Celestial Bodies that Cleomedes lived in the Hellespont on the Black Sea, suggesting the city of Lysimachia.
- Neugebauer admits that the city of Lysimachia was destroyed in 144 BC which seems at odds with his own date of 370 AD for Cleomedes but he is able to show that despite the disaster of 144 BC records of the city certainly extend up to the fourth century AD.
- The weakness of Neugebauer's argument must surely be that almost all of Cleomedes' text and data is taken from the works of others so Neugebauer's arguments seem only to give strong evidence for one of Cleomedes' sources having written in Lysimachia.
Born about 10 AD possibly Lysimachia, Hellespont, Greece (now Turkey). Died about 70 AD.
View full biography at MacTutor
Tags relevant for this person:
Ancient Greek, Astronomy, Origin Turkey
Adapted from other CC BY-SA 4.0 Sources:
- O’Connor, John J; Robertson, Edmund F: MacTutor History of Mathematics Archive