A module on Nicholas Copernicus and his view of the universe.
Copernicus The first speculations about the possibility of the Sun being
the center of the cosmos and the Earth being one of the planetsgoing around it go back to the third century BCE. In his
Sand-Reckoner , Archimedes (d. 212 BCE), discusses
how to express very large numbers. As an example he chooses thequestion as to how many grains of sand there are in the
cosmos. And in order to make the problem more difficult, hechooses not the geocentric cosmos generally accepted at the
time, but the heliocentric cosmos proposed by Aristarchus ofSamos (ca. 310-230 BCE), which would have to be many times
larger because of the lack of observable stellar parallax. Weknow, therefore, that already in Hellenistic times thinkers were
at least toying with this notion, and because of its mention inArchimedes's book Aristarchus's speculation was well-known in
Europe beginning in the High Middle Ages but not seriouslyentertained until Copernicus.
Copernicus European learning was based on the Greek sources that had been
passed down, and cosmological and astronomical thought werebased on Aristotle and
Ptolemy .
Aristotle's cosmology of a central Earth surrounded byconcentric spherical shells carrying the planets and fixed stars
was the basis of European thought from the 12th century CEonward. Technical astronomy, also geocentric, was based on the
constructions of excentric circles and epicycles codified inPtolemy's
Almagest (2d. century CE).
In the fifteenth century, the reform of European astronomy was
begun by the astronomer/humanist Georg Peurbach (1423-1461) andhis student Johannes Regiomontanus (1436-1476). Their efforts
(like those of their colleagues in other fields) wereconcentrated on ridding astronomical texts, especially
Ptolemy's, from errors by going back to the original Greek textsand providing deeper insight into the thoughts of the original
authors. With their new textbook and a guide to the
Almagest , Peurbach and Regiomontanus raised the
level of theoretical astronomy in Europe.
Several problems were facing astronomers at the beginning of the
sixteenth century. First, the tables (by means of which topredict astronomical events such as eclipses and conjunctions)
were deemed not to be sufficiently accurate. Second, Portugueseand Spanish expeditions to the Far East and America sailed out
of sight of land for weeks on end, and only astronomical methodscould help them in finding their locations on the high
seas. Third, the calendar, instituted by Julius Caesar in 44 BCEwas no longer accurate. The equinox, which at the time of the
Council of Nicea (325 CE) had fallen on the 21st, had nowslipped to the 11th. Since the date of Easter (the celebration
of the defining event in Christianity) was determined withreference to the equinox, and since most of the other religious
holidays through the year were counted forward or backward fromEaster, the slippage of the calendar with regard to celestial
events was a very serious problem. For the solution to all threeproblems, Europeans looked to the astronomers.
OpenStax, Galileo project. OpenStax CNX. Jul 07, 2004 Download for free at http://cnx.org/content/col10234/1.1
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