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astronomical unit

(Encyclopedia)astronomical unit (AU), mean distance between the earth and sun; one AU is c.92,960,000 mi (149,604,970 km). The astronomical unit is the principal unit of measurement within the solar system, e.g., M...

Astronomical Ephemeris

(Encyclopedia)Astronomical Ephemeris: see ephemeris. ...

thermal unit

(Encyclopedia)thermal unit: see British thermal unit. ...

astronomical coordinate systems

(Encyclopedia)astronomical coordinate systems. A coordinate system is a method of indicating positions. Each coordinate is a quantity measured from some starting point along some line or curve, called a coordinate ...

Infrared Astronomical Satellite

(Encyclopedia)Infrared Astronomical Satellite: see infrared astronomy. ...

Orbiting Astronomical Observatory

(Encyclopedia)Orbiting Astronomical Observatory (OAO), series of four orbiting observatories (see observatory, orbiting) launched between 1966 and 1972 by the National Aeronautics and Space Administration (NASA) to...

atomic mass unit

(Encyclopedia)atomic mass unit or amu, in chemistry and physics, unit defined as exactly 1⁄12 the mass of an atom of carbon-12, the isotope of carbon with six protons and six neutrons in its nucleus. One amu is e...

European Currency Unit

(Encyclopedia)European Currency Unit: see European Monetary System. ...

British thermal unit

(Encyclopedia)British thermal unit, abbr. Btu, unit for measuring heat quantity in the customary system of English units of measurement, equal to the amount of heat required to raise the temperature of one pound of...

solar constant

(Encyclopedia)solar constant, the average amount of radiant energy received by the earth's atmosphere from the sun; its value is about 2 calories per min incident on each square centimeter of the upper atmosphere. ...