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helium

(Encyclopedia)helium hēˈlēəm [key], gaseous chemical element; symbol He; at. no. 2; at. wt. 4.0026; m.p. below −272℃ at 26 atmospheres pressure; b.p. −268.934℃ at 1 atmosphere pressure; density 0.1785 g...

chemical bond

(Encyclopedia)chemical bond, mechanism whereby atoms combine to form molecules. There is a chemical bond between two atoms or groups of atoms when the forces acting between them are strong enough to lead to the for...

fuel

(Encyclopedia)fuel, material that can be burned or otherwise consumed to produce heat. The common fuels used in industry, transportation, and the home are burned in air. The carbon and hydrogen in fuel rapidly comb...

volcano

(Encyclopedia)volcano, vents or fissures in the earth's crust through which gases, molten rock, or lava, and solid fragments are discharged. Their study is called volcanology. The term volcano is commonly applied b...

space medicine

(Encyclopedia)space medicine, study of the medical and biological effects of space travel on living organisms. The principal aim is to discover how well and for how long humans can withstand the extreme conditions ...

atmosphere

(Encyclopedia)CE5 Atmosphere atmosphere [Gr.,=sphere of air], the mixture of gases surrounding a celestial body with sufficient gravity to maintain it. Although some details about the atmospheres of other plane...

element

(Encyclopedia)CE5 element, in chemistry, a substance that cannot be decomposed into simpler substances by chemical means. A substance such as a compound can be decomposed into its constituent elements by means o...

metal

(Encyclopedia)metal, chemical element displaying certain properties by which it is normally distinguished from a nonmetal, notably its metallic luster, the capacity to lose electrons and form a positive ion, and th...

fire fighting

(Encyclopedia)fire fighting, the use of strategy, personnel, and apparatus to extinguish, to confine, or to escape from fire. Ancient Rome is known to have had a fire department consisting by the 1st cent. of app...

Mars, in astronomy

(Encyclopedia)Mars, in astronomy, 4th planet from the sun, with an orbit next in order beyond that of the earth. Mars has two natural satellites, discovered by Asaph Hall in 1877. The innermost of these, Phobos...