|
Solar
Elemental Abundances
|
| Element |
Number % |
Mass %
|
|
| Hydrogen |
92.0 |
73.4
|
| Helium |
7.8 |
25.0
|
| Carbon |
0.02 |
0.20
|
| Nitrogen |
0.008 |
0.09
|
| Oxygen |
0.06 |
0.8
|
| Neon |
0.01 |
0.16
|
| Magnesium |
0.003 |
0.06
|
| Silicon |
0.004 |
0.09
|
| Sulfur |
0.002 |
0.05
|
| Iron |
0.003 |
0.14 | | Although
we cannot sample the Sun directly, we can learn a great deal about its
composition from the pattern of absorption lines in its spectrum (the Frauenhofer lines).
The pattern of these lines serves as a set of fingerprints for the
elements that are present in the surface of the Sun, and their intensity
serves as a measure of the concentration of these elements.
The Solar AbundancesApproximately
60 elements have been thus identified in the solar spectrum. The most
abundant are listed in the adjacent table, both with respect to the number
of atoms or ions present, and with respect to the total mass of the atoms
or ions. The Sun is clearly mostly hydrogen and helium, with only a trace
of heavier elements. This is also true of the Universe as a whole: most of
the Universe is hydrogen, with some helium, and the remainder of the
elements occur only in trace concentrations. In that sense the composition
of the Earth is highly unrepresentative of the rest of the Universe.
The Discovery of HeliumThe
element helium is the second most abundant in both the Sun and the
Universe, but it is very difficult to find on the Earth. In fact, helium
was discovered in the spectrum of the Sun (the name helium derives from helios,
which is the Greek name for the Sun). It was postulated that a set of
spectral lines observed in the Solar emission spectrum that could not be
associated with any known element belonged to a new element (the Sun is
too cool to ionize helium appreciably, so absorption lines associated with
helium are very weak). Only after this was helium discovered on the Earth
and this hypothesis confirmed (helium occurs in certain very deep gas
wells on the Earth). |