Liber astronomicus served as the leading textbook of the
early Renaissance. It was in fact Bonatti who was chosen
by DANTEto represent astrology in the eighth circle of the
Inferno, where he was depicted with his head on back-
wards and no ability to see ahead.
Interest in astrology continued to grow and was well
served by the newly developed printing press. Almanacs
had appeared before GUTENBERGbut after he issued the
first printed copy in 1448 they emerged with much greater
frequency, variety, and number. However, they often pro-
voked the hostility of an officialdom prone to suspect par-
tisan motives behind political predictions. For this reason
Pope Sixtus V issued a bull in 1586 condemning judicial
astrology. In England the lucrative trade of almanac pub-
lishing was made the monopoly of the Stationers’ Com-
pany, through which the state was able to exercise control
over the content of the publications.
Scientific opinion appeared divided: such early Re-
naissance scholars as Nicholas CUSANUSand PICO DELLA
MIRANDOLAwere critical, but astronomers of the standing
of RHETICUS, KEPLER, and BRAHEopenly practiced as as-
trologers. It may have been, however, that in some cases
their intellectual commitment was less urgent than their
need to subsidize their astronomical researches. Astrology
as a scientific discipline barely outlived the Renaissance.
By the time of Isaac Newton, at the end of the 17th cen-
tury, astronomers had begun already to rewrite their his-
tory and to dismiss much of their past, although Newton
himself had an interest in the occult, including astrology.
Further reading: Anthony Grafton, Cardano’s Cosmos:
The Worlds and Works of a Renaissance Astrologer (Cam-
bridge, Mass.: Harvard University Press, 2000).
astronomy The scientific study of celestial bodies (com-
pare ASTROLOGY). At the beginning of the Renaissance,
scholars accepted unquestioningly the COSMOLOGY of
Aristotle and the astronomy of Ptolemy (see PTOLEMAIC
SYSTEM). These views formed the background to DANTE’s
Divine Comedy and, more prosaically, were found ex-
pressed in the numerous editions of the popular 13th-
century text, the De sphaera of Sacrobosco.
The first tasks facing the astronomers of the Renais-
sance were to acquaint themselves with the details of an-
cient astronomy and to develop new mathematical
techniques to describe better the complexities of planetary
motion. To this end such scholars as PEURBACH, RE-
GIOMONTANUS, and RHETICUSsought to establish accurate
texts of Ptolemy’s Almagest and related works, and to mas-
ter and deploy the new language of TRIGONOMETRY, to as-
tronomical observations. There followed developments
which, by the time of the death of GALILEO(1642), had
completely transformed man’s view of the heavens. The
traditional view that they were immutable and incorrupt-
ible was called into question by the discovery in 1572 by
Tycho BRAHEof a NEW STAR. Even more damaging were the
observations in 1610 by Galileo of the formerly unsus-
pected satellites of Jupiter, and the presence of mountains
and craters on the moon. Further evidence of celestial cor-
ruptibility came in 1611 with Christoph SCHEINER’s o b -
servations of sunspots. Additional difficulties were
presented by the comet of 1577. Careful observation by
Brahe revealed it to be a genuine feature of the heavens
and not, as Aristotle had supposed, a transitory atmos-
pheric phenomenon.
Behind much of this success there lay an enormous
improvement in the instruments available to astronomers.
Brahe at his Uraniborg observatory developed such tradi-
tional instruments as ARMILLARY SPHERESand QUADRANTS
to the limits inherent in naked-eye observation. The great-
est advance, however, came with the invention of the
TELESCOPEearly in the 17th century. First applied to the
heavens in 1610 by Galileo, it rapidly became the most
fundamental tool of astronomy. Equally significant was
the increasing accuracy of astronomical observations.
Early Renaissance astronomers had relied upon the Alfon-
sine Tables (1252). When COPERNICUScame to apply them
in 1504 to an expected conjunction of Mars and Saturn he
found the tables to be as much as 10 days adrift. They con-
tinued in use, however, until 1551 when they were re-
placed by the Prutenic Tables compiled by Erasmus
REINHOLD, the first tables to be based on the Copernican
hypothesis. These, in turn, were superseded by the
Rudolfine Tables (1627) which were prepared by Brahe
and KEPLERand were to remain in use for the rest of the
17th century.
The period also saw an advance in the system of stel-
lar nomenclature. Copernicus and his colleagues had, in
the manner of Ptolemy, referred to stars as being located in
the head, tail, or foot of a particular constellation. The
modern system of identifying stars alphabetically by their
brightness was introduced by Johann BAYERin Uranome-
tria (1603) and found quick support.
Equally significant were the more theoretical innova-
tions associated with Copernicus and his successors. Since
antiquity planetary orbits were taken as unquestionably
circular, with the planets themselves, and all other heav-
enly bodies, moving with a pleasingly simple uniform
motion around a central, stationary earth. In 1543
Copernicus initiated the first great astronomical revolu-
tion of modern science by replacing the central earth of
antiquity with an equally stationary sun. The resulting he-
liocentric system remained dependent upon the tradi-
tional circular orbits of antiquity. Nor were they
questioned by Brahe or Galileo. The break eventually
came with Kepler. After spending several years trying to
establish the orbit of Mars he finally saw that by assuming
planets to move in elliptical orbits he would finally be able
to make sense of the available data. He went on to propose
in 1609 his first law: planets move in elliptical orbits, with
the sun occupying one focus. Two other laws were formu-aassttrroonnoommyy 3355