![NGC 6543](https://upload.wikimedia.org/wikipedia/commons/9/9c/NGC_6543_%22Cat%27s_Eye%22.png)
Nebulium was a proposed
element found in
astronomical observation
Observational astronomy is a division of astronomy that is concerned with recording data about the observable universe, in contrast with theoretical astronomy, which is mainly concerned with calculating the measurable implications of physical m ...
of a
nebula
A nebula ('cloud' or 'fog' in Latin; pl. nebulae, nebulæ or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral or molecular hydrogen and also cosmic dust. Nebulae are often star-forming regio ...
by
William Huggins
Sir William Huggins (7 February 1824 – 12 May 1910) was an English astronomer best known for his pioneering work in astronomical spectroscopy together with his wife, Margaret.
Biography
William Huggins was born at Cornhill, Middlesex, in ...
in 1864. The strong green
emission lines of the
Cat's Eye Nebula
The Cat's Eye Nebula (also known as NGC 6543 and Caldwell 6) is a planetary nebula in the northern constellation of Draco, discovered by William Herschel on February 15, 1786. It was the first planetary nebula whose spectrum was investigated by t ...
, discovered using
spectroscopy
Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...
, led to the postulation that an as yet unknown element was responsible for this emission. In 1927,
Ira Sprague Bowen
Ira Sprague Bowen (December 21, 1898 – February 6, 1973) was an American physicist and astronomer. In 1927 he discovered that nebulium was not really a chemical element but instead doubly ionized oxygen.
Life and work
Bowen was born in Sen ...
showed that the lines are emitted by
doubly ionized oxygen
In astronomy and atomic physics, doubly ionized oxygen is the ion O2+ (O III in spectroscopic notation). Its emission forbidden lines in the visible spectrum fall primarily at the wavelength 500.7 nm, and secondarily at 495.9 nm. Before ...
(O
2+), and no new element was necessary to explain them.
History
William Hyde Wollaston
William Hyde Wollaston (; 6 August 1766 – 22 December 1828) was an English chemist and physicist who is famous for discovering the chemical elements palladium and rhodium. He also developed a way to process platinum ore into malleable ingo ...
in 1802 and
Joseph von Fraunhofer
Joseph Ritter von Fraunhofer (; ; 6 March 1787 – 7 June 1826) was a German physicist and optical lens manufacturer. He made optical glass, an achromatic telescope, and objective lenses. He also invented the spectroscope and developed diffract ...
in 1814 described the dark lines within the
solar spectrum. Later,
Gustav Kirchhoff
Gustav Robert Kirchhoff (; 12 March 1824 – 17 October 1887) was a German physicist who contributed to the fundamental understanding of electrical circuits, spectroscopy, and the emission of black-body radiation by heated objects.
He coine ...
explained the lines by
atomic absorption or emission, which allowed the lines to be used for the identification of
chemical element
A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species. Unlike chemical compounds, chemical elements cannot be broken down into simpler sub ...
s.
In the early days of telescopic
astronomy
Astronomy () is a natural science that studies astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...
, the word
nebula
A nebula ('cloud' or 'fog' in Latin; pl. nebulae, nebulæ or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral or molecular hydrogen and also cosmic dust. Nebulae are often star-forming regio ...
was used to describe any fuzzy patch of light that did not look like a star. Many of these, such as the
Andromeda Nebula, had
spectra that looked like stellar spectra, and these turned out to be
galaxies
A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. ...
. Others, such as the
Cat's Eye Nebula
The Cat's Eye Nebula (also known as NGC 6543 and Caldwell 6) is a planetary nebula in the northern constellation of Draco, discovered by William Herschel on February 15, 1786. It was the first planetary nebula whose spectrum was investigated by t ...
, had very different spectra. When
William Huggins
Sir William Huggins (7 February 1824 – 12 May 1910) was an English astronomer best known for his pioneering work in astronomical spectroscopy together with his wife, Margaret.
Biography
William Huggins was born at Cornhill, Middlesex, in ...
looked at the Cat's Eye, he found no continuous spectrum like that seen in the Sun, but just a few strong
emission line
A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...
s. The two green lines at 495.9
nm and 500.7 nm were the strongest. These lines did not correspond to any known elements on Earth. The fact that
helium
Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
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
Margaret Lindsay, Lady Huggins (14 August 1848, in Dublin – 24 March 1915, in London),
born Margaret Lindsay Murray, was an Irish-English scientific investigator and astronomer.
With her husband William Huggins she was a pioneer in the field o ...
in a short communication in 1898, although it is stated that her husband occasionally used the term before.
In 1911,
John William Nicholson
John William Nicholson, FRS (1 November 1881 – 3 October 1955) was an English mathematician and physicist. Nicholson is noted as the first to create an atomic model that quantized angular momentum as h/2π. Nicholson was also the first to crea ...
theorized that all known elements consisted of four protoelements, one of which was Nebulium.
The development of the
periodic table
The periodic table, also known as the periodic table of the (chemical) elements, is a rows and columns arrangement of the chemical elements. It is widely used in chemistry, physics, and other sciences, and is generally seen as an icon of ch ...
by
Dimitri Mendeleev and the determination of the atomic numbers by
Henry Moseley
Henry Gwyn Jeffreys Moseley (; 23 November 1887 – 10 August 1915) was an English physicist, whose contribution to the science of physics was the justification from physical laws of the previous empirical and chemical concept of the atomic num ...
in 1913 left nearly no room for a new element. In 1914 French astronomers were able to determine the
atomic weight
Relative atomic mass (symbol: ''A''; sometimes abbreviated RAM or r.a.m.), also known by the deprecated synonym atomic weight, is a dimensionless physical quantity defined as the ratio of the average mass of atoms of a chemical element in a giv ...
of nebulium. With a measured value of 2.74 for the lines near 372 nm and a slightly lower value for the 500.7 nm line indicating two elements responsible for the spectrum.
Ira Sprague Bowen
Ira Sprague Bowen (December 21, 1898 – February 6, 1973) was an American physicist and astronomer. In 1927 he discovered that nebulium was not really a chemical element but instead doubly ionized oxygen.
Life and work
Bowen was born in Sen ...
was working on
UV spectroscopy
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...
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 transition
In spectroscopy, a forbidden mechanism (forbidden transition or forbidden line) is a spectral line associated with absorption or emission of photons by atomic nuclei, atoms, or molecules which undergo a transition that is not allowed by a particul ...
s. They were shown as due to
doubly ionized oxygen
In astronomy and atomic physics, doubly ionized oxygen is the ion O2+ (O III in spectroscopic notation). Its emission forbidden lines in the visible spectrum fall primarily at the wavelength 500.7 nm, and secondarily at 495.9 nm. Before ...
at extremely low density, rather than the hypothetical nebulium. As
Henry Norris Russell
Henry Norris Russell ForMemRS HFRSE FRAS (October 25, 1877 – February 18, 1957) was an American astronomer who, along with Ejnar Hertzsprung, developed the Hertzsprung–Russell diagram (1910). In 1923, working with Frederick Saunders, he deve ...
put it, "Nebulium has vanished into thin air." Nebulae are typically extremely
rarefied
Rarefaction is the reduction of an item's density, the opposite of compression. Like compression, which can travel in waves (sound waves, for instance), rarefaction waves also exist in nature. A common rarefaction wave is the area of low relati ...
, 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.
See also
*
Coronium
Coronium, also called newtonium, was the name of a suggested chemical element, hypothesised in the 19th century. The name, inspired by the solar corona, was given by Gruenwald in 1887. A new atomic thin green line in the solar corona was then con ...
*
Helium
Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
References
{{reflist, 25em
Misidentified chemical elements
Oxygen
Nebulae