Editing Nebula (section)

==Observational history==

[[File:Hs-2009-25-e-full.jpg|thumb|right|Portion of the [[Carina Nebula]]]]

Around 150 AD, [[Ptolemy]] recorded, in books VII–VIII of his ''[[Almagest]]'', five stars that appeared nebulous. He also noted a region of nebulosity between the [[constellation]]s [[Ursa Major]] and [[Leo (constellation)|Leo]] that was not associated with any [[star]].<ref>{{citation
  | first=P. | last=Kunitzsch | date=1987
  | title=A Medieval Reference to the Andromeda Nebula
  | journal=[[ESO Messenger]]
  | volume=49 | pages=42–43
  | url=http://www.eso.org/sci/publications/messenger/archive/no.49-sep87/messenger-no49-42-43.pdf
  | bibcode=1987Msngr..49...42K | access-date=2009-10-31 }}</ref> The first true nebula, as distinct from a [[star cluster]], was mentioned by the [[Astronomy in the medieval Islamic world|Muslim Persian astronomer]] [[Abd al-Rahman al-Sufi]] in his ''[[Book of Fixed Stars]]'' (964).<ref name=Jones>{{Cite book|title=Messier's nebulae and star clusters|author=Jones, Kenneth Glyn |publisher=Cambridge University Press|date=1991|isbn=0-521-37079-5|page=1}}</ref> He noted "a little cloud" where the [[Andromeda Galaxy]] is located.<ref name="rasqj25">{{cite journal
  | last=Harrison | first=T. G. |date=March 1984
  | title=The Orion Nebula&nbsp;– where in History is it
  | journal=[[Quarterly Journal of the Royal Astronomical Society]]
  | volume=25 | issue=1 | pages=70–73
  | bibcode=1984QJRAS..25...65H }}</ref> He also cataloged the [[Omicron Velorum Cluster|Omicron Velorum]] star cluster as a "nebulous star" and other nebulous objects, such as [[Brocchi's Cluster]].<ref name=Jones/> The [[supernovas]] that created the [[Crab Nebula]], [[SN 1054]], was observed by Arabic and [[Chinese astronomy|Chinese astronomers]] in 1054.<ref name="Lundmark">{{cite journal | last1 = Lundmark | first1 = K | year = 1921 | title = Suspected New Stars Recorded in the Old Chronicles and Among Recent Meridian Observations | journal = Publications of the Astronomical Society of the Pacific | volume = 33 | issue = 195 | page = 225 | bibcode = 1921PASP...33..225L | doi = 10.1086/123101 | doi-access = free }}</ref><ref name="Mayall">{{cite journal | last1 = Mayall | first1 = N.U. | year = 1939 | title = The Crab Nebula, a Probable Supernova | url = http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1939ASPL....3..145M&link_type=ARTICLE&db_key=AST| journal = Astronomical Society of the Pacific Leaflets | volume = 3 | issue = 119 | page = 145 | bibcode = 1939ASPL....3..145M }}</ref>

In 1610, [[Nicolas-Claude Fabri de Peiresc]] discovered the [[Orion Nebula]] using a telescope. This nebula was also observed by [[Johann Baptist Cysat]] in 1618. However, the first detailed study of the Orion Nebula was not performed until 1659 by [[Christiaan Huygens]], who also believed he was the first person to discover this nebulosity.<ref name="rasqj25" />

In 1715, [[Edmond Halley]] published a list of six nebulae.<ref> {{cite journal
  | last=Halley | first=E. | date=1714–1716
  | volume=XXXIX | journal= [[Philosophical Transactions]]
  | pages=390–92 | title=An account of several nebulae or lucid spots like clouds, lately discovered among the fixed stars by help of the telescope}} </ref> This number steadily increased during the century, with [[Jean-Philippe de Cheseaux]] compiling a list of 20 (including eight not previously known) in 1746. From 1751 to 1753, [[Nicolas-Louis de Lacaille]] cataloged 42 nebulae from the [[Cape of Good Hope]], most of which were previously unknown. [[Charles Messier]] then compiled a catalog of 103 "nebulae" (now called [[Messier object]]s, which included what are now known to be galaxies) by 1781; his interest was detecting [[comet]]s, and these were objects that might be mistaken for them.<ref name="hoskin2005">{{cite journal| last=Hoskin | first=Michael | date=2005| title=Unfinished Business: William Herschel's Sweeps for Nebulae | journal=[[British Journal for the History of Science]] | volume=43 | issue=3 | pages=305–320 | bibcode=2005HisSc..43..305H | doi=10.1177/007327530504300303 | s2cid=161558679 }}</ref>

The number of nebulae was then greatly increased by the efforts of [[William Herschel]] and his sister, [[Caroline Herschel]]. Their ''Catalogue of One Thousand New Nebulae and Clusters of Stars''<ref>{{cite book|title=Philosophical Transactions|url=https://archive.org/details/philosophicaltr04unkngoog|year=1786|publisher=T.N.|page=[https://archive.org/details/philosophicaltr04unkngoog/page/n479 457]}}</ref> was published in 1786. A second catalog of a thousand was published in 1789, and the third and final catalog of 510 appeared in 1802. During much of their work, William Herschel believed that these nebulae were merely unresolved clusters of stars. In 1790, however, he discovered a star surrounded by nebulosity and concluded that this was a true nebulosity rather than a more distant cluster.<ref name="hoskin2005" />

Beginning in 1864, [[William Huggins]] examined the spectra of about 70 nebulae. He found that roughly a third of them had the [[emission spectrum]] of a [[gas]]. The rest showed a continuous spectrum and were thus thought to consist of a mass of stars.<ref>{{cite book
  | author=Watts, William Marshall
  | author2=Huggins, Sir William
  | author3=Lady Huggins | title=An introduction to the study of spectrum analysis
  | publisher=Longmans, Green, and Co.
  | date=1904
  | pages=[https://archive.org/details/anintroductiont00hugggoog/page/n106 84]–85 | access-date=2009-10-31
  | url=https://archive.org/details/anintroductiont00hugggoog
}}</ref><ref name="struve37">{{cite journal
  | last=Struve | first=Otto | date=1937
  | title=Recent Progress in the Study of Reflection Nebulae | journal=Popular Astronomy | volume=45
  | pages=9–22 | bibcode=1937PA.....45....9S }}</ref> A third category was added in 1912 when [[Vesto Slipher]] showed that the spectrum of the nebula that surrounded the star [[Merope (star)|Merope]] matched the spectra of the [[Pleiades]] [[open cluster]]. Thus, the nebula radiates by reflected star light.<ref>{{cite journal
  | last=Slipher | first=V. M. | date=1912
  | title=On the spectrum of the nebula in the Pleiades
  | journal=Lowell Observatory Bulletin | volume=1
  | pages=26–27 | bibcode=1912LowOB...2...26S }}</ref>

In 1923, following the [[Great Debate (astronomy)|Great Debate]], it became clear that many "nebulae" were in fact galaxies far from the [[Milky Way]].

Slipher and [[Edwin Hubble]] continued to collect the spectra from many different nebulae, finding 29 that showed emission spectra and 33 that had the continuous spectra of star light.<ref name="struve37" /> In 1922, Hubble announced that nearly all nebulae are associated with stars and that their illumination comes from star light. He also discovered that the emission spectrum nebulae are nearly always associated with stars having spectral classifications of B or hotter (including all [[O-type main sequence star]]s), while nebulae with continuous spectra appear with cooler stars.<ref>{{cite journal
  | last=Hubble | first=E. P. |date=December 1922
  | title=The source of luminosity in galactic nebulae.
  | journal=Astrophysical Journal | volume=56
  | pages=400–438 
  | doi=10.1086/142713 | bibcode=1922ApJ....56..400H
| doi-access=free}}</ref> Both Hubble and [[Henry Norris Russell]] concluded that the nebulae surrounding the hotter stars are transformed in some manner.<ref name="struve37" />