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(UV)--electromagnetic radiation resembling visible light, but of shorter wavelength. UV cannot be seen by the eye, and much of it is absorbed by ozone, a variant of oxygen, at altitudes of 30-40 km. Satellite telescopes, however, can and do view stars and the Sun in UV, and even in the extreme UV (EUV), the range between UV and X-rays.
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A circle of radius=1 around the origin of (x,y) coordinates, used for extending the definition of trigonometric functions to angles larger than 90 degrees.
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A vector of unit length. Vectors have both magnitude and direction, but in some calculations it is convenient to separate the two. Denoting vector by an underline, a vector V can be represented by two factors multiplying each other, a unit vector Vu giving just the direction, and a magnitude V, i.e., the vector is V=VuV.
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In the final rapid collapse of a supernova, the energy release causes nuclear reactions. Most of the energy then does not produce heating, but is instead drained away as neutrinos. Heat would have counteracted the star's collapse, but the "Urca process" by which the energy is drained away allows it to proceed very rapidly. It is therefore responsible for the supernova "explosion."
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