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1) Nucleus formed by the α-process (q.v.) (see even-even nuclei.)
2) Particle first discovered in radioactive α decay, and later identified as helium nuclei (two protons and two neutrons bound together.)
3) The nucleus of a 4He atom, consisting of two protons and two neutrons. Mass of α-particle 4.00260 amu.
Industry:Astronomy
Controlling the shape of a telescope mirror at a relatively slow rate.
Industry:Astronomy
Compensating for atmospheric distortions in a wavefront by high-speed changes in the shape of a small, thin mirror.
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
