Changes

As scientific knowledge progressed, understanding of the term "planet" changed from something that moved across the sky (in relation to the [[fixed star|starfield]]), to a body that orbited the Earth (or that were believed to do so at the time). When the [[heliocentric model]] gained sway in the 16th century, it became accepted that a planet was actually something that directly orbited the [[Sun]]. Thus the Earth was itself a planet, http://galileo.rice.edu/sci/theories/copernican_system.html, Copernican The Galileo Project while the Sun and [[Moon]] were not.  Since they do not directly "orbit the Sun". At the end of the 17th century, when the first satellites of Saturn were discovered, the terms "planet" and "satellite" were at first used interchangeably, although "satellite" would gradually become more prevalent in the following century. "A Discovery of two'' New Planets ''about'' Saturn, ''made in the Royal Parisian Observatory by Signor'' Cassini, ''Fellow of both the Royal Societys, of'' England ''and'' France; ''English't out of French.''

As scientific knowledge progressed, understanding of the term "planet" changed from something that moved across the sky (in relation to the [[fixed star|starfield]]), to a body that orbited the Earth (or that were believed to do so at the time). When the [[heliocentric model]] gained sway in the 16th century, it became accepted that a planet was actually something that directly orbited the [[Sun]]. Thus the Earth was itself a planet, http://galileo.rice.edu/sci/theories/copernican_system.html, Copernican The Galileo Project while the Sun and [[Moon]] were not.  Since they do not directly "orbit the Sun". At the end of the 17th century, when the first satellites of Saturn were discovered, the terms "planet" and "satellite" were at first used interchangeably, although "satellite" would gradually become more prevalent in the following century. "A Discovery of two'' New Planets ''about'' Saturn, ''made in the Royal Parisian Observatory by Signor'' Cassini, ''Fellow of both the Royal Societys, of'' England ''and'' France; ''English't out of French.''

http://links.jstor.org/sici?sici=0370-2316%281673%298%3C5178%3AADOTNP%3E2.0.CO%3B2-Z . This journal became the Philosophical Transactions of the Royal Society of London in 1775. There may just be earlier publications within the '' Until the mid-19th century, any newly discovered object orbiting the Sun was listed with the planets by the scientific community, and the number of "planets" swelled rapidly towards the end of that period.

[http://links.jstor.org/sici?sici=0370-2316%281673%298%3C5178%3AADOTNP%3E2.0.CO%3B2-Z] . This journal became the Philosophical Transactions of the Royal Society of London in 1775. There may just be earlier publications within the '' Until the mid-19th century, any newly discovered object orbiting the Sun was listed with the planets by the scientific community, and the number of "planets" swelled rapidly towards the end of that period.

During the 1800s, astronomers began to realize most recent discoveries were unlike the traditional planets. They shared the same [[asteroid belt|region of space]], between [[Mars]] and [[Jupiter]], and had a far smaller mass. Bodies such as [[Ceres (dwarf planet)|Ceres]], [[2 Pallas|Pallas]], and [[4 Vesta|Vesta]], which had been classed as planets for almost half a century, became classified with the new designation "[[asteroid]]." From this point, a "planet" came to be understood, in the absence of any formal definition, as any "large" body that orbited the Sun. There was no apparent need to create a set limit, as  there was a dramatic size gap between the asteroids and the planets, and the spate of new discoveries seemed to have ended after the discovery of [[Neptune]] in 1846.<ref> http://aa.usno.navy.mil/hilton/AsteroidHistory/minorplanets.html. When Did the Asteroids Become Minor Planets? U.S. Naval Observatory  

During the 1800s, astronomers began to realize most recent discoveries were unlike the traditional planets. They shared the same [[asteroid belt|region of space]], between [[Mars]] and [[Jupiter]], and had a far smaller mass. Bodies such as [[Ceres (dwarf planet)|Ceres]], [[2 Pallas|Pallas]], and [[4 Vesta|Vesta]], which had been classed as planets for almost half a century, became classified with the new designation "[[asteroid]]." From this point, a "planet" came to be understood, in the absence of any formal definition, as any "large" body that orbited the Sun. There was no apparent need to create a set limit, as  there was a dramatic size gap between the asteroids and the planets, and the spate of new discoveries seemed to have ended after the discovery of [[Neptune]] in 1846.<ref> http://aa.usno.navy.mil/hilton/AsteroidHistory/minorplanets.html. When Did the Asteroids Become Minor Planets? U.S. Naval Observatory