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dark energy

(Encyclopedia)dark energy, repulsive force that opposes the self-attraction of matter (see gravitation) and causes the expansion of the universe to accelerate. The search for dark energy was triggered by the discov...

free energy

(Encyclopedia)free energy or Gibbs free energy, quantity derived from the relationships between heat and work studied in thermodynamics and used as a measure of the relative stability of a physical or chemical syst...

geothermal energy

(Encyclopedia)geothermal energy: see energy, sources of. ...

atomic energy

(Encyclopedia)atomic energy: see nuclear energy. ...

nuclear energy

(Encyclopedia)CE5 Graph of binding energy per nucleon as a function of mass number nuclear energy, the energy stored in the nucleus of an atom and released through fission, fusion, or radioactivity. In these pr...

kinetic energy

(Encyclopedia)kinetic energy: see energy.

activation energy

(Encyclopedia)CE5 Energy profile of an exothermic reaction: Although the total energy of the products is less than that of the reactants, the activation energy must be added to weaken or break existing bonds bef...

thermonuclear energy

(Encyclopedia)thermonuclear energy: see nuclear energy. ...

sun, in astronomy

(Encyclopedia)CE5 Structure of the sun sun, intensely hot, self-luminous body of gases at the center of the solar system. Its gravitational attraction maintains the planets, comets, and other bodies of the sola...

apparent solar time

(Encyclopedia)apparent solar time: see solar time. ...