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Index (A)
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AC - AC
AD - AF
AG - AJ
AK - AM
AN - AN
AO - AR
AS - AV
AW - AZ
Moment of truth
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The Sun, with a diameter of 1,392,000 km, is made of 94% hydrogen atoms. |
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aphelion Astron.
The point at which an object, such as a planet or comet, orbiting the Sun which is farthest from the Sun.
apoapsis Astron.
The point at which an object orbiting a celestial body that is farthest from that body.
apogee Astron.
The point at which an object orbiting the Earth that is farthest from the Earth.
Apollo asteroid Astron.
An asteroid whose orbit intersects that of Earth. Named after asteroid 1862 Apollo. More precise definition for an Apollo asteroid is that its semi-major axis is larger than 1.0 AU and its perihelion distance is less than 1.017 AU.
apoptosis Biol.
See necrobiosis.
aqua regia Chem.
A mixture of acid made of one part concentrated nitric acid (HNO3) and three parts of concentrated hydrochloric acid (HCl), by volume. The individual acidic components when separated do not react with gold. However, in the presence of both nitrate and chloride ions, aqua regia can slowly dissolves gold.
arc Math.
A segment along the circumference of a circle, a portion of a curve.
Archimedes's principle Phys.
A buoyancy principle which states that when a body is wholy or partly submerged in a liquid, it experiences an upthrust or buoyant force equals
to the weight of the displaced quantity of liquid.
arene Chem.
Also known as aromatic hydrocarbon, an organic compound that contains at least one aromatic ring such as bezene, methylbenzene (toluene), naphthalene, etc.
arithmatic mean Math.
Of a given n numbers, which can be negative or positive, their sum divided by n:
AO - AR
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