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radioactive silvery metal which does not occur naturally
Industry:Astronomy
1) Unit of electric current. "The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 × 10-7 newton per meter of length" CIPM 1946, Resolution 2, approved by the 9th CGPM 1948). A current of 1 A is equivalent to the passage along the filament of a light bulb of about 6 × 1018 electronic charges per second.
2) constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 × 10-7 newton per meter of length
Industry:Astronomy
1) The angular momentum of a system about a specified origin is the sum over all the particles in the system (or an integral over the different elements of the system if it is continuous) of the vector products of the radius vector joining each particle to the origin and the momentum of the particle. For a closed system it is conserved by virtue of the isotropy of space.
2) The product of mass and angular velocity for an object in rotation; similar to linear momentum. In quantum mechanics, angular momentum is quantized, i.e., is measured in indivisible units equivalent to Planck's constant divided by 2 pi. This corresponds classically to only certain frequencies of rotation being allowed.
Industry:Astronomy
The angle subtended by an object on the sky. For example, the angular size of the moon is 30 arcminutes.
Industry:Astronomy
The condition in which the universe appears different in different directions.
Industry:Astronomy
1) A solar eclipse in which the solar disk is never completely covered but is seen as an annulus or ring at maximum eclipse. An annular eclipse occurs when the apparent disk of the Moon is smaller than that of the Sun.
2) An eclipse of the Sun in which the Moon is too far from Earth to block out the Sun completely, so that a ring of sunlight appears around the Moon.
Industry:Astronomy
The interval between two successive perigee passages of the Moon.
Industry:Astronomy
1) A period of time based on the revolution of the Earth around the Sun, where a year is defined as the mean interval between successive passages of the Earth through perihelion.
2) The interval between two successive perihelion passages of Earth.
Industry:Astronomy
