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1) In Aristotelian physics, the fifth element, of which the stars and planets are made.
2) In Classical physics, an invisible medium that was thought to suffuse all space.
Industry:Astronomy
Light in the nighttime sky caused by the collision of atoms and molecules (primarily oxygen, OH, and Ne) in Earth's geocorona with charged particles and X-rays from the Sun or outer space. The airglow varies with time of night, latitude, and season. It is a minimum at zenith and maximum about 10?above the horizon.
Industry:Astronomy
Art of bringing parts of the universe to the perfect state toward which they were thought to aspire - e.g., gold for metals, immortality for human beings.
Industry:Astronomy
Element in the second column of the periodic table (from the left.)
Industry:Astronomy
1) Spontaneous emission by a heavier element (such as uranium) of positively charged helium nuclei - alpha particles - comprising 2 protons and 2 neutrons. The result of this radioactive decay is that the original element is very gradually converted into another element, with a decreased atomic number and mass. Alpha particle emission may be simultaneous with beta particle decay.
2) The disintegration of an atomic nucleus, in which the final products are an alpha particle and a nucleus with two fewer protons and two fewer neutrons than the original.
Industry:Astronomy
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
A hypothetical process of nucleosynthesis, which consisted of redistributing α-particles in the region from neon 20 to iron 56 (and perhaps slightly higher). The α-process has been replaced by explosive and nonexplosive C, O, and Si burning occurring in rapidly evolving or even explosive stages of stellar evolution which at higher temperatures and densities becomes the e-process.
Industry:Astronomy
A form of mounting similar to that of a radar which allows the telescope tube to be moved horizontally (by rotation in azimuth or compass direction) and vertically (by rotation in altitude or elevation). To follow a star the telescope must be adjusted simultaneously in both axes. (also called alt-az.)
Industry:Astronomy
