Editing Galaxy (section)

=== Milky Way ===
{{Main|Milky Way}}

[[Greek philosophy|Greek]] philosopher [[Democritus]] (450–370 BCE) proposed that the bright band on the night sky known as the Milky Way might consist of distant stars.<ref name="Plutarch"/>
[[Aristotle]] (384–322 BCE), however, believed the Milky Way was caused by "the ignition of the fiery exhalation of some stars that were large, numerous and close together" and that the "ignition takes place in the upper part of the [[atmosphere]], in the [[Sublunary sphere|region of the World that is continuous with the heavenly motions]]."<ref name=Montada/> [[Neoplatonism|Neoplatonist]] philosopher [[Olympiodorus the Younger]] ({{circa|495}}–570 CE) was critical of this view, arguing that if the Milky Way was [[sublunary]] (situated between Earth and the Moon) it should appear different at different times and places on Earth, and that it should have [[parallax]], which it did not. In his view, the Milky Way was celestial.<ref name=heidarzadeh23 />

According to Mohani Mohamed, [[Astronomy in the medieval Islamic world|Arabian]] astronomer [[Ibn al-Haytham]] (965–1037) made the first attempt at observing and measuring the Milky Way's parallax,<ref name=Mohamed /> and he thus "determined that because the Milky Way had no parallax, it must be remote from the Earth, not belonging to the atmosphere."<ref name=Bouali_et_al_2008/> [[Persian people|Persian]] astronomer [[al-Biruni]] (973–1048) proposed the Milky Way galaxy was "a collection of countless fragments of the nature of nebulous stars."<ref name=al-Biruni/> [[Al-Andalus|Andalusian]] astronomer [[Avempace]] ({{abbr|d.|died}} 1138) proposed that it was composed of many stars that almost touched one another, and appeared to be a continuous image due to the effect of [[refraction]] from sublunary material,<ref name=Montada /><ref name="heidarzadeh25" /> citing his observation of the [[Conjunction (astronomy and astrology)|conjunction]] of Jupiter and Mars as evidence of this occurring when two objects were near.<ref name=Montada /> In the 14th century, Syrian-born [[Ibn Qayyim al-Jawziyya]] proposed the Milky Way galaxy was "a myriad of tiny stars packed together in the sphere of the fixed stars."<ref name=Livingston/>

Actual proof of the Milky Way consisting of many stars came in 1610 when the Italian astronomer [[Galileo Galilei]] used a [[optical telescope|telescope]] to study it and discovered it was composed of a huge number of faint stars.<ref name=Galilei/><ref name="O'Connor_Robertson_2002"/> In 1750, English astronomer [[Thomas Wright (astronomer)|Thomas Wright]], in his ''An Original Theory or New Hypothesis of the Universe'', correctly speculated that it might be a rotating body of a huge number of stars held together by [[gravitation]]al forces, akin to the [[Solar System]] but on a much larger scale, and that the resulting disk of stars could be seen as a band on the sky from a perspective inside it.{{efn|Wright called the Milky Way the ''Vortex Magnus'' (Great Whirlpool) and estimated its diameter to be 8.64×10<sup>12</sup> miles (13.9×10<sup>12</sup> km).{{sfn|Wright|1750|p=73}}}}{{sfn|Wright|1750|pp=48–}}<ref name="our_galaxy" /> In his 1755 treatise, [[Immanuel Kant]] elaborated on Wright's idea about the Milky Way's structure.<ref name=Kant_1755/> [[File:Herschel-Galaxy.png|thumb|The shape of the Milky Way as estimated from star counts by [[William Herschel]] in 1785; the Solar System was assumed to be near the center.]]

The first project to describe the shape of the Milky Way and the position of the Sun was undertaken by [[William Herschel]] in 1785 by counting the number of stars in different regions of the sky. He produced a diagram of the shape of the galaxy with [[Galactocentrism|the Solar System close to the center]].<ref name=Herschel_1785/><ref name=paul1993 /> Using a refined approach, [[Jacobus Kapteyn|Kapteyn]] in 1920 arrived at the picture of a small (diameter about 15&nbsp;kiloparsecs) ellipsoid galaxy with the Sun close to the center. A different method by [[Harlow Shapley]] based on the cataloguing of [[globular cluster]]s led to a radically different picture: a flat disk with diameter approximately 70&nbsp;kiloparsecs and the Sun far from the centre.<ref name="our_galaxy" /> Both analyses failed to take into account the [[extinction (astronomy)|absorption of light]] by [[cosmic dust|interstellar dust]] present in the [[galactic plane]]; but after [[Robert Julius Trumpler]] quantified this effect in 1930 by studying [[open cluster]]s, the present picture of the Milky Way galaxy emerged.<ref name=Trimble_1999/>