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Oxygen is the most abundant chemical element by mass in the Earth's biosphere, air, sea and land. Oxygen is the third most abundant chemical element in the universe, after hydrogen and helium. [68] About 0.9% of the Sun's mass is oxygen. [19]
The 2.7 million Kelvin photon temperature gives a typical photon energy of 250 electronvolt, thereby setting a typical mass scale for warm dark matter: particles much more massive than this, such as GeV–TeV mass WIMPs, would become non-relativistic much earlier than one year after the Big Bang and thus have FSLs much smaller than a ...
For a non-rotating white dwarf, it is equal to approximately 5.7 M ☉ / μ e 2, where μ e is the average molecular weight per electron of the star. [ 47 ] : eqn.(63) As the carbon-12 and oxygen-16 that predominantly compose a carbon–oxygen white dwarf both have atomic numbers equal to half their atomic weight , one should take μ e equal to ...
The discovery of isotopes of oxygen in 1929 required a more precise definition of the unit. Two distinct definitions came into use. Chemists choose to define the AMU as 1 / 16 of the average mass of an oxygen atom as found in nature; that is, the average of the masses of the known isotopes, weighted by their natural abundance.
Dark oxygen production refers to the generation of molecular oxygen (O 2) through processes that do not involve light-dependent oxygenic photosynthesis.The name therefore uses a different sense of 'dark' than that used in the phrase "biological dark matter" (for example) which indicates obscurity to scientific assessment rather than the photometric meaning.
Much more precise measurements from WMAP in 2003–2010 have continued to support the standard model and give more accurate measurements of the key parameters. The term "dark energy", echoing Fritz Zwicky 's "dark matter" from the 1930s, was coined by Michael S. Turner in 1998.
The standard atomic weight takes into account the isotopic distribution of the element in a given sample (usually assumed to be "normal"). For example, water has a molar mass of 18.0153(3) g/mol, but individual water molecules have molecular masses which range between 18.010 564 6863(15) Da ( 1 H
Darkness is the condition resulting from a lack of illumination, or an absence of visible light. Human vision is unable to distinguish colors in conditions of very low luminance because the hue -sensitive photoreceptor cells on the retina are inactive when light levels are insufficient, in the range of visual perception referred to as scotopic ...