View source for Nebulium

{{Short description|Proposed element found in astronomical observation of a nebula}}
[[File:NGC6543.jpg|thumb|right|Cat's Eye Nebula (NGC 6543)]]
[[File:NGC 6543 "Cat's Eye".png|thumb|Cat's Eye Nebula (NGC 6543)]]
'''Nebulium''' was a proposed [[chemical element|element]] found in [[astronomical observation]] of a [[nebula]] by [[William Huggins]] in 1864. The strong green [[emission spectrum|emission]] lines of the [[Cat's Eye Nebula]], discovered using [[spectroscopy]], led to the postulation that an as yet unknown element was responsible for this emission. In 1927, [[Ira Sprague Bowen]] showed that the lines are emitted by [[doubly ionized oxygen]] (new style [[oxygen|O]]{{sup|2+}}; old style O{{sup|III}}), and no new element was necessary to explain them.

==History==

[[William Hyde Wollaston]] in 1802 and [[Joseph von Fraunhofer]] in 1814 described the dark lines within the [[sun|solar]] spectrum. Later, [[Gustav Kirchhoff]] explained the lines by [[Atomic absorption spectroscopy|atomic absorption]] or emission, which allowed the lines to be used for the identification of [[chemical element]]s.

In the early days of telescopic [[astronomy]], the word [[nebula]] was used to describe any fuzzy patch of light that did not look like a star. Many of these, such as the [[Andromeda Galaxy|Andromeda Nebula]], had [[Astronomical spectroscopy|spectra]] that looked like stellar spectra, and these turned out to be [[galaxies]]. Others, such as the [[Cat's Eye Nebula]], had very different spectra. When [[William Huggins]] looked at the Cat's Eye, he found no continuous spectrum like that seen in the Sun, but just a few strong [[emission line]]s. The two green lines at 495.9&nbsp;[[nanometer|nm]] and 500.7&nbsp;nm were the strongest.<ref>{{cite journal
 |last1=Huggins |first1=William
 |last2=Miller |first2=William A.
 |year=1864
 |title=On the Spectra of some of the Nebulae
 |journal=[[Philosophical Transactions of the Royal Society of London]]
 |volume=154 |pages=437–444 
 |doi=10.1098/rstl.1864.0013
 |bibcode=1864RSPT..154..437H
 |jstor=108876
|doi-access=free
 }}</ref> These lines did not correspond to any known elements on Earth. The fact that [[helium]] had been identified by the emission lines in the Sun in 1868, and had then also been found on Earth in 1895, encouraged astronomers to suggest that the lines were due to a new element. The name ''nebulium'' (occasionally ''nebulum'' or ''nephelium'') was first mentioned by [[Margaret Lindsay Huggins]] in a short communication in 1898, although it is stated that her husband occasionally used the term before.<ref>{{cite journal
 |title=.... Teach me how to name the .... light
 |last1=Huggins |first1=Margaret L.
 |year=1898
 |journal=[[Astrophysical Journal]]
 |volume=8 |pages=54
 |doi=10.1086/140540
 |bibcode=1898ApJ.....8R..54H
|doi-access=free
 }}</ref> 

In 1911, [[John William Nicholson]] theorized that all known elements consisted of four protoelements, one of which was Nebulium.<ref>{{cite journal
 |last= Nicholson |first=John William
 |year = 1911
 |title = A structural theory of the chemical elements
 |journal = [[Philosophical Magazine]]
 |volume = 22 | issue = 132 |pages = 864–889
 |doi = 10.1080/14786441208637185
|url = https://zenodo.org/record/1430908
 }}</ref><ref>{{cite journal
 |last= McCormmach  |first = Russell
 |year = 1966 
 |title = The atomic theory of John William Nicholson
 |journal = [[Archive for History of Exact Sciences]]
 |volume = 3 | issue = 2 |pages = 160–184
 |doi = 10.1007/BF00357268 |s2cid = 120797894
 }}</ref>
The development of the [[periodic table]] by [[Dimitri Mendeleev]] and the determination of the atomic numbers by [[Henry Moseley]] in 1913 left nearly no room for a new element.<ref>{{cite journal
 |last=Heilbron |first=John L.
 |year=1966 
 |title=The Work of H. G. J. Moseley 
 |journal=[[Isis (journal)|Isis]]
 |volume=57 |issue=3 |pages=336–364
 |jstor=228365
 |doi = 10.1086/350143
|s2cid=144765815
 }}</ref> In 1914 French astronomers were able to determine the [[atomic weight]] of nebulium. A measured value of 2.74 for the lines near 372&nbsp;nm and a slightly lower value for the 500.7&nbsp;nm line seemed to indicate that two elements were responsible for the spectrum.<ref>{{cite journal
 |last1=Buisson |first1=Hervé
 |last2=Fabry |first2=Charles
 |last3=Bourget |first3= Henry
 |year=1914
 |title=An application of interference to the study of the Orion nebula.
 |journal=[[Astrophysical Journal]]
 |volume=40 |pages=241–258
 |doi=10.1086/142119
 |bibcode=1914ApJ....40..241B
|doi-access=free
 }}</ref>

[[Ira Sprague Bowen]] was working on [[UV spectroscopy]] and on the calculation of spectra of the light elements of the periodic table when he became aware of the green lines discovered by Huggins. With this knowledge he was able to suggest that the green lines might be [[Forbidden mechanism|forbidden transition]]s. They were shown as due to [[doubly ionized oxygen]] at extremely low density,<ref>{{cite journal
 |last=Bowen |first=Ira Sprague
 |year=1927
 |title=The Origin of the Nebulium Spectrum
 |journal=[[Nature (journal)|Nature]]
 |volume=120 |page=473
 |doi=10.1038/120473a0
|bibcode = 1927Natur.120..473B
 |issue=3022|doi-access=free
 }}</ref> rather than the hypothetical nebulium.  As [[Henry Norris Russell]] put it, "Nebulium has vanished into thin air." Nebulae are typically extremely [[Vacuum|rarefied]], much less dense than the hardest vacuums produced on Earth. In these conditions, lines can form which are suppressed at normal densities. These lines are known as forbidden lines, and are the strongest lines in most nebular spectra.<ref>{{cite journal
 |last=Hirsh |first=Richard F.
 |year=1979
 |title=The Riddle of the Gaseous Nebulae
 |journal=[[Isis (journal)|Isis]]
 |volume=70 |issue=2 |pages=197–212
 |doi=10.1086/352195
 |bibcode=1979Isis...70..197H
 |jstor=230787
|s2cid=123234614
 }}</ref>

== See also ==
*[[Coronium]]
*[[Helium]]

==References==
{{reflist|25em}}

[[Category:Misidentified chemical elements]]
[[Category:Oxygen]]
[[Category:Nebulae]]