Solar abundance

Fig. 3. The 3He abundances (by number relative to hydrogen), j/3 = 10B(3He/H), derived from Galactic H n regions [4], as a function of galactocentric distance (filled circles). Also shown for comparison is the solar system abundance (solar symbol). The open circles are the oxygen abundances for the same H n regions (and for the Sun).

The epoch and mode of galaxy formation are not well known, but both quasars and star-forming galaxies are known with redshifts up to about 7, corresponding to an era when the expanding Universe was only 1/8 of its present size, and the emission-line spectra of quasars indicate a large heavy-element abundance (solar or more Hamann Ferland 1999), suggesting prior stellar activity. The first stars, on the other hand, known as Population IIP, would have been devoid of metals whether they differed from normal stars in other basic characteristics, notably their mass distribution, is not known, since no completely metal-free stars have been... 

The abundant solar energy resources are challenging potential option for hydrogen production. The solar cell costs are important element of the PV economic viability. The modules account for about 50% of cost of a PV power plant. The solar cells themselves account about half of the module cost, or 20% of total system cost. Thin film polycrystalline technology may make possible to have the module cost about 50 USD/m and electricity price of 6 cents/kWh. This is only a planning target for 10% efficiency. 

As seen in Eq. 1, the water-splitting reaction has an overall energy requirement of 4.92 eV per O2 molecule formed (or +474.7 kj/mol O2 formed). The most abundant solar radiation to strike the earth s surface falls in the visible range (750-400 nm) and fortunately, these photons are energetic enough (1.65-3.1 eV)27 so that as little as two photons are required to drive this process thermodynamically. When broken down into redox half-reactions (5 and 6), the multi-electron nature of reaction 1 is readily apparent. 

Comparison of meteorite and solar abundances Solar system abundances versus mass number. 03.1.5.3 Other sources for solar system abundances THE ABUNDANCES OF THE ELEMENTS IN THE ISM. 2.1 Introduction. 2.2 The Nature of the ISM. 2.3 The Chemical Composition of the ISM... 

Keywords solar system abundances, solar photosphere, meteorites, Cl chondrites... 

Contribution of s- and r-process to the solar abundances of the isobars for heavy elements (p-isotopes cannot be seen in this figure because of their very small abundances). Solar system abundances are measured (Anders and Grevesse 1989), s- and r-abundances are calculated. The peaks in the solar abundances around mass numbers A = 88,138, 208 are formed in the s-process, whereas the broader companion peaks shifted to slightly lower mass number are r-process peaks... 

The most abundant solar radiation absorbent gas of the atmosphere, by far, is O2. Its absorption spectrum was shown in Fig. 5.3, and the most important reaction is photodissociation to create O atoms, reaction (5.18). 

The most abundant literature is that bearing on solar eneigy conversion, mainly centered on the use of Ru(2,2 -bipyridine)3 and its analogues. The excited state of the parent compound was found some years ago to be a powerful reducing agent [212], allowing the following spontaneous reactions to be written ... 

Sodium is present in fair abundance in the sun and stars. The D lines of sodium are among the most prominent in the solar spectrum. Sodium is the fourth most abundant element on earth, comprising about 2.6% of the earth s crust it is the most abundant of the alkali group of metals. 

Percentage of meteorites seen to fall. Chondrites. Over 90% of meteorites that are observed to fall out of the sky are classified as chondrites, samples that are distinguished from terrestrial rocks in many ways (3). One of the most fundamental is age. Like most meteorites, chondrites have formation ages close to 4.55 Gyr. Elemental composition is also a property that distinguishes chondrites from all other terrestrial and extraterrestrial samples. Chondrites basically have undifferentiated elemental compositions for most nonvolatile elements and match solar abundances except for moderately volatile elements. The most compositionaHy primitive chondrites are members of the type 1 carbonaceous (Cl) class. The analyses of the small number of existing samples of this rare class most closely match estimates of solar compositions (5) and in fact are primary source solar or cosmic abundances data for the elements that cannot be accurately determined by analysis of lines in the solar spectmm (Table 2). Table 2. Solar System Abundances of the Elements ... 

Fig. 2. The plot of total reduced iron, Fe, and oxidized iron, Fe, normalized to Si abundance shows how the chondrite classes fall into groups distinguished by oxidation state and total Fe Si ratio. The soHd diagonal lines delineate compositions having constant total Fe Si ratios of 0.6 and 0.8. The fractionation of total Fe Si is likely the result of the relative efficiencies of accumulation of metal and siUcate materials into the meteorite parent bodies. The variation in oxidation state is the result of conditions in the solar nebula when the soHds last reacted with gas. Terms are defined in Table 1 (3).

Extraterrestrial dust particles can be proven to be nonterrestrial by a variety of methods, depending on the particle si2e. Unmelted particles have high helium. He, contents resulting from solar wind implantation. In 10-)J.m particles the concentration approaches l/(cm g) at STP and the He He ratio is close to the solar value. Unmelted particles also often contain preserved tracks of solar cosmic rays that are seen in the electron microscope as randomly oriented linear dislocations in crystals. Eor larger particles other cosmic ray irradiation products such as Mn, Al, and Be can be detected. Most IDPs can be confidently distinguished from terrestrial materials by composition. Typical particles have elemental compositions that match solar abundances for most elements. TypicaUy these have chondritic compositions, and in descending order of abundance are composed of O, Mg, Si, Ee, C, S, Al, Ca, Ni, Na, Cr, Mn, and Ti. 

A photovoltaic cell (often called a solar cell) consists of layers of semiconductor materials with different electronic properties. In most of today s solar cells the semiconductor is silicon, an abundant element in the earth s crust. By doping (i.e., chemically introducing impurity elements) most of the silicon with boron to give it a positive or p-type electrical character, and doping a thin layer on the front of the cell with phosphorus to give it a negative or n-type character, a transition region between the two types... 

An allotrope of oxygen, ozone, 03 (8), is formed in the stratosphere by the effect of solar radiation on 02 molecules. Its total abundance in the atmosphere is equivalent to a layer that, at the ordinary conditions of 25°C and 1 bar, would cover the Earth to a thickness of only 3 mm, yet its presence in the stratosphere is vital to the maintenance of life on Earth (see Box 13.3). Ozone can be made in the laboratory by passing an electric discharge through oxygen. It is a blue gas that... 

Na is likely deposited in the upper atmosphere by meteors along with other metals (Clemesha et al., 1981) and distributed by solar winds (Happer et al., 1994). This atomic layer is "eaten away" at its bottom by chemical reactions (e.g. molecule and aggregate formation). Fe, Al, Ca are more abundant than Na, but the D2 transition is so strong that it provides the largest product of column density CNa and transition cross section, nominally 10 — 10" atoms/cm. The layer has been studied mostly with Lidar technique (Blamont and Donahue, 1961 Albano et al., 1970 Bowman et al., 1969 Sarrazin, 2001). 

The composition of the Earth was determined both by the chemical composition of the solar nebula, from which the sun and planets formed, and by the nature of the physical processes that concentrated materials to form planets. The bulk elemental and isotopic composition of the nebula is believed, or usually assumed to be identical to that of the sun. The few exceptions to this include elements and isotopes such as lithium and deuterium that are destroyed in the bulk of the sun s interior by nuclear reactions. The composition of the sun as determined by optical spectroscopy is similar to the majority of stars in our galaxy, and accordingly the relative abundances of the elements in the sun are referred to as "cosmic abundances." Although the cosmic abundance pattern is commonly seen in other stars there are dramatic exceptions, such as stars composed of iron or solid nuclear matter, as in the case with neutron stars. The... 

Table 2-1 Solar abundances of the elements (atoms/lO atoms of Si)...

---