Editing Definition of planet (section)

=== Planets in antiquity ===
[[File:Apparent retrograde motion of Mars in 2003.gif|thumb|The motion of 'lights' moving across the background of stars is the basis of the classical definition of planets: wandering stars.]]
While knowledge of the planets predates history and is common to most civilizations, the word ''planet'' dates back to [[ancient Greece]]. Most Greeks believed the Earth to be stationary and at the center of the universe in accordance with the [[geocentric model]] and that the objects in the sky, and indeed the sky itself, revolved around it (an exception was [[Aristarchus of Samos]], who put forward an early version of [[heliocentrism]]). Greek astronomers employed the term {{lang|grc|ἀστέρες πλανῆται}} ({{Transliteration|grc|asteres planetai}}), 'wandering stars',<ref>{{cite web|url=http://www.m-w.com/dictionary/planet|title=Definition of planet|publisher=Merriam-Webster OnLine|access-date=July 23, 2007}}</ref><ref>{{cite web|url=http://www.wordsources.info/words-mod-planets.html|title=Words For Our Modern Age: Especially words derived from Latin and Greek sources|publisher=Wordsources.info|access-date=July 23, 2007}}</ref> to describe those starlike lights in the heavens that moved over the course of the year, in contrast to the {{lang|grc|ἀστέρες ἀπλανεῖς}} ({{Transliteration|grc|asteres aplaneis}}), the '[[fixed stars]]', which stayed motionless relative to one another. The five bodies currently called "planets" that were known to the Greeks were those visible to the naked eye (from [[apparent magnitude|brightest to dimmest]]): [[Venus]], [[Jupiter]], [[Mercury (planet)|Mercury]], [[Mars]], and [[Saturn]]. 
Graeco-Roman [[Timeline of cosmology|cosmology]] commonly considered seven planets, with the Sun and the Moon counted among them (as is the case in modern [[Planets in astrology|astrology]]); however, there is some ambiguity on that point, as many ancient astronomers distinguished the five star-like planets from the Sun and Moon. As the 19th-century German naturalist [[Alexander von Humboldt]] noted in his work ''[[Cosmos (Humboldt)|Cosmos]]'',

<blockquote>Of the seven cosmical bodies which, by their continually varying relative positions and distances apart, have ever since the remotest antiquity been distinguished from the "unwandering orbs" of the heaven of the "fixed stars", which to all sensible appearance preserve their relative positions and distances unchanged, five only—Mercury, Venus, Mars, Jupiter and Saturn—wear the appearance of stars—"''cinque stellas errantes''"—while the Sun and Moon, from the size of their disks, their importance to man, and the place assigned to them in mythological systems, were classed apart.<ref>{{cite book |title=Cosmos: A Sketch of a Physical Description of the Universe |author=Alexander von Humboldt |year=1849 |work=digitised 2006 |url=https://archive.org/details/cosmosasketchap00humbgoog |page=[https://archive.org/details/cosmosasketchap00humbgoog/page/n337 297] |access-date=2007-07-23 |publisher=H.G. Bohn |isbn=978-0-8018-5503-0}}</ref></blockquote>
In his ''[[Timaeus (dialogue)|Timaeus]]'', written in roughly 360&nbsp;[[BCE]], [[Plato]] mentions, "the Sun and Moon and five other stars, which are called the planets".<ref>{{cite web|title=Timaeus by Plato|work=The Internet Classics|url=http://classics.mit.edu/Plato/timaeus.html|access-date= February 22, 2007}}</ref> His student [[Aristotle]] makes a similar distinction in his ''[[On the Heavens]]'': "The movements of the sun and moon are fewer than those of some of the planets".<ref>{{cite web|title=On the Heavens by Aristotle, Translated by J. L. Stocks, volume II|work=University of Adelaide Library|url=https://ebooks.adelaide.edu.au/a/aristotle/heavens/book2.html|year=2004|access-date=February 24, 2007|archive-date=August 23, 2008|archive-url=https://web.archive.org/web/20080823061709/http://ebooks.adelaide.edu.au/a/aristotle/heavens/book2.html|url-status=dead}}</ref> In his ''Phaenomena'', which set to verse an astronomical treatise written by the philosopher [[Eudoxus of Cnidus|Eudoxus]] in roughly 350&nbsp;BCE,<ref>{{cite web|title=Phaenomena Book I&nbsp;— ARATUS of SOLI|url=http://www.geocities.com/astrologysources/classicalgreece/phaenomena/index.htm|access-date=June 16, 2007|archive-url = https://web.archive.org/web/20050901044449/http://www.geocities.com/astrologysources/classicalgreece/phaenomena/index.htm |archive-date = September 1, 2005|url-status=dead}}</ref> the poet [[Aratus]] describes "those five other orbs, that intermingle with [the constellations] and wheel wandering on every side of the twelve figures of the Zodiac."<ref>{{cite web|author=Aratus |title=Phaemonema|translator=A. W. & G. R. Mair |work=theoi.com|url=http://www.theoi.com/Text/AratusPhaenomena.html|access-date=June 16, 2007}}</ref>

In his ''[[Almagest]]'' written in the 2nd century, [[Claudius Ptolemy|Ptolemy]] refers to "the Sun, Moon and five planets."<ref>{{cite book|title=The Almagest |author=Ptolemy|translator=R. Gatesby Taliaterro|publisher= University of Chicago Press|year= 1952|page=270}}</ref> [[Gaius Julius Hyginus|Hyginus]] explicitly mentions "the five stars which many have called wandering, and which the Greeks call Planeta."<ref name=planeta>{{cite web|title=Astra Planeta|author=theoi.com|url=http://www.theoi.com/Titan/AstraPlaneta.html|access-date=February 25, 2007}}</ref> [[Marcus Manilius]], a Latin writer who lived during the time of [[Caesar Augustus]] and whose poem ''Astronomica'' is considered one of the principal texts for modern [[astrology]], says, "Now the [[dodecatemory]] is divided into five parts, for so many are the stars called wanderers which with passing brightness shine in heaven."<ref>{{cite book|author=Marcus Manilius |translator=G. P. Goold |title=Astronomica|publisher=Harvard University Press|year=1977|page=141}}</ref>

The single view of the seven planets is found in [[Cicero]]'s ''[[Dream of Scipio]]'', written sometime around 53&nbsp;BCE, where the spirit of [[Scipio Africanus]] proclaims, "Seven of these spheres contain the planets, one planet in each sphere, which all move contrary to the movement of heaven."<ref>{{cite web|title=The Dream of Scipio|author=Cicero|work=Roman Philosophy |translator=Richard Hooker|url=http://www.wsu.edu/~dee/ROME/SCIPIO.HTM|year=1996|access-date=June 16, 2007|archive-url=https://web.archive.org/web/20070703203835/http://www.wsu.edu/~dee/ROME/SCIPIO.HTM |archive-date=July 3, 2007}}</ref> In his ''[[Natural History (Pliny)|Natural History]]'', written in 77&nbsp;CE, [[Pliny the Elder]] refers to "the seven stars, which owing to their motion we call planets, though no stars wander less than they do."<ref>{{cite book|title=Natural History vol 1|author=IH Rackham|publisher=William Heinemann Ltd.|year=1938|page= 177, viii}}</ref> [[Nonnus]], the 5th century Greek poet, says in his ''[[Dionysiaca]]'', "I have oracles of history on seven tablets, and the tablets bear the names of the seven planets."<ref name=planeta />