NATS 1740 Chapter Notes -Triple-Alpha Process, Inverse-Square Law, Electron Degeneracy Pressure

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Published on 13 Apr 2013
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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
decrease the apparent brightness by a factor of 2 or 22
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
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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 protonproton 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
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Document Summary

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/ 4 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 decrease the apparent brightness by a factor of 2 or 22.

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