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Astronomy Definitions.docx

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York University
Natural Science
NATS 1740
Randy Hoffman

Astronomy Definitions Gravitational equilibrium: Is the outward push or the internal gas pressure and the inward pull of gravity. Sunspots: Are dark spots on the suns surface Corona: The outermost layer of the sun, several million km from the visible surface. Photosphere: Lowest layer, visible surface of the sun, temperature lower than 6000K Core: The central region of a star, in which nuclear fusion can occur Nuclear fusion: Fusing two or more nuclei into 1 Solar flares: send bursts of x-rays and fast moving charged particles into space Luminosity: The total amount of power a star emits into space Parallax: The apparent shifting of an object against the background due to viewing it from different positions Inverse square law: apparent brightness = luminosity/ 4π x (distance)2 , The apparent brightness of a star or any other light source obeys the inverse square law. Doubling the distance to a star would 2 decrease the apparent brightness by a factor of 2 or 2 Spectral type: Determined from spectral lies present in star system (OBAFGKM) Main sequence: The prominent streak running from the upper left to the lower right on the HR diagram Supergiant: Very large and bright stars located on the top right of the H-R diagram. White dwarf: White dwarf stars are the cooling embers of stars that have exhausted their fuel for nuclear fusion. (Located at the lower left of H-R Diagram) H-R diagram: An HR diagram plots the surface temperatures of stars against their luminosities Open clusters: Modest sized, younger, found in galactic disk Globular clusters: Densely packed, older, found in the halo Main-sequence turnoff point: point on HR diagram at which the Pleiades main sequence diverges from the standard main sequence Brown dwarf: An object too small to become an ordinary star because electron degeneracy pressure halts its gravitational collapse before fusion becomes self-sustaining and have a mass less than 0.08M Thermal pressure: The ordinary pressure in a gas arising from motions of particles that can be attributed to the objects temperature Degeneracy pressure: Does not depend on temperature, it depends on quantum mechanics. It is the outward pressure from the core. Exclusion principle: The law of quantum mechanics that states that two fermions cannot occupy the same quantum state at the same time Shell fusion: Planetary nebula: A cloud of gas Proton-proton chain: reactions by which stars convert hydrogen to helium, The proton–proton chain dominates in stars the size of the Sun or smaller. Triple-alpha process: The triple alpha process is a set of nuclear fusion reactions by which three helium- 4 nuclei (alpha particles) are transformed into carbon CNO cycle: Aka, Carbon, Nitrogen, Oxygen cycle. It is one of two sets of fusion reactions by which stars convert hydrogen to helium Massive star supernova: Occurs when a massive star explodes Neutron star: the ball of neutrons created by the collapse of the iron core in a massive star super nova Pulsar: is a rotating neutron star that beams radiation along its magnetic axis Nova: The dramatic brightening of a star that lasts for a few weeks and then subsides; it occurs when a burst of hydrogen fusion ignites in a shell on the surface of an accreting white dwarf in the binary star system. White dwarf supernova: When a white dwarf exceeds the mass of 1.4 it ignites and the star explodes Black hole: A black hole is a place where gravity is so strong that nothing, not even light can escape from within it. Event horizon: The boundary between the inside of the black hole and the universe outside Schwarzschild radius : radius of event horizon (looking from outside and depends on its mass) time dilation: The effect in which you observe time running more slowly in reference frames moving relative to you length contraction: The effect in which you observe lengths to be shortene
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