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contain neutrons (except H , where only a minority of its atoms have one neutron accompanying the proton; these isotopes of H are called deuterium). An atom of a given element always has the same number of protons, but the number of neutrons can vary. For example, U has two isotopes, or kind of atoms, with combined proton and neutron numbers of 235 and 238. Of those, 92 are always protons. 1



Figure 3 shows the number of isotopes for each element. Like the elemental abundances in Figure 2, the number of isotopes reveals a corresponding up-anddown pattern. A low number of stable isotopes for odd numbered elements means a lower overall elemental abundance compared to the even numbered neighboring elements. This is a simplified explanation for the oddeven abundance distribution noted by Harkins and Oddo.

photosphere. When the white light of the Sun is broken through a prism, its spectrum of colors becomes visible—just as sunlight breaking through the rain to give a rainbow. A very detailed inspection of the color spectrum shows that there are “dark” bars; where color is missing. The light from the Sun has to pass through the Sun’s outermost layers, and the elements in those layers absorb some of the light at specific colors, or wavelengths, which gives the characteristic absorption lines of an element in the spectrum. However, some elements have only weak or blended absorption lines and are difficult to measure. In 1929, the American astronomer Henry Norris Russell (1877-1957) reported the abundances of 56 elements in the solar photosphere. (Happy 80th birthday to the first quantitative analysis of elements in the Sun!) Ancient rocks—meteorites


bout 200 years ago, it was accepted that meteorites were dust grain-sized to trailer-sized asteroid fragments falling to Earth. At that time, the periodic table did not exist and many elements had yet to be discovered. Over time it became clear that rocks—both terrestrial and from space—are mainly comprised of only a few elements.

Take something


By 1847, the French geologist Élie de Beaumont (1798-1874) had assembled a list for the known elements of the time. He found there were 16 elements that are the most distributed ones over the Earth’s surface...The surface of the Earth encloses in all its parts everything that is essential for the existence of meteorites organized beings; it provides a new and striking example of the harmony that exists in all parts of nature. The 16 elements can be found in volcanic productions, in mineral waters, and one sees that nature has provided not only a settlement but also the conservation of this indispensable harmony. The aging Earth will never cease to furnish all the elements to the organized beings necessary for their existence.1

and something tiny the

Sun and

Data on abundances—where from?


o what should we analyze to get the elemental abundances in the solar system? Take something huge and something tiny—the Sun and meteorites. The Sun is a good representative for the overall elemental composition of the solar system, occupying more than 99% of its total mass. Many elements can be analyzed in the Sun by measuring the strengths of their absorption lines in the light emitted from the solar

About 20 years later, spectroscopy revealed the same elements in comets, the Sun and other stars. It became apparent that the elements in different celestial objects do not occur at random. Around the same

Figure 3 (Facing Page). The number of isotopes for each element. The element mass numbers are on the vertical axis and the corresponding element symbols are laid in the background. The horizontal axis has no scale as the number of boxes representing the isotopes of each element is still easily countable. The color indicates if the sum of protons and neutrons is an even number (bluishpurple) or uneven number (yellowish). Courtesy of the author.

Profile for M. Hurst

GLIMPSE | vol 2.4, winter 2009-10 | Cosmos  

The "Cosmos" issue investigates the history and technologies of seeing beyond Earth's atmosphere. From Mayan and pre-Christian civilizations...

GLIMPSE | vol 2.4, winter 2009-10 | Cosmos  

The "Cosmos" issue investigates the history and technologies of seeing beyond Earth's atmosphere. From Mayan and pre-Christian civilizations...