Unit 2 Test Study Guide PDF

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Study guide for test on unit 2....

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energy balance (in a star) The balance between the rate at which fusion releases energy in the star’s core and the rate at which the star’s surface radiates this energy into space. conduction (of energy) The process by which thermal energy is transferred by direct contact from warm material to cooler material. convection The energy transport process in which warm material expands and rises while cooler material contracts and falls. solar wind A stream of charged particles ejected from the Sun. solar prominences Vaulted loops of hot gas that rise above the Sun’s surface and follow magnetic field lines. solar flares Huge and sudden releases of energy on the solar surface, probably caused when energy stored in magnetic fields is suddenly released. coronal mass ejections Bursts of charged particles from the Sun’s corona that travel outward into space. stellar parallax The apparent shift in the position of a nearby star (relative to distant objects) that occurs as we view the star from different positions in Earth’s orbit of the Sun each year. apparent magnitude A measure of the apparent brightness of an object in the sky, based on the ancient system developed by Hipparchus. absolute magnitude A measure of an object’s luminosity; defined to be the apparent magnitude the object would have if it were located exactly 10 parsecs away. visual binary

A binary star system in which both stars can be resolved through a telescope. spectroscopic binary A binary star system whose binary nature is revealed because we detect the spectral lines of one or both stars alternately becoming blueshifted and redshifted as the stars orbit each other. interstellar medium The gas and dust that fills the space between stars in a galaxy. ionization nebula A colorful, wispy cloud of gas that glows because neighboring hot stars irradiate it with ultraviolet photons that can ionize hydrogen atoms; also called an emission nebula or H II region. reflection nebula A nebula that we see as a result of starlight reflected from interstellar dust grains. Reflection nebulae tend to have blue and black tints. interstellar reddening The change in the color of starlight as it passes through dusty gas. The light appears redder because dust grains absorb and scatter blue light more effectively than red light. electron degeneracy pressure Degeneracy pressure exerted by electrons, as in brown dwarfs and white dwarfs. brown dwarf An object too small to become an ordinary star because electron degeneracy pressure halts its gravitational collapse before fusion becomes self-sustaining; brown dwarfs have mass less than

0.08Msun. helium flash The event that marks the sudden onset of helium fusion in the previously inert helium core of a low-mass star.

helium fusion The fusion of three helium nuclei to form one carbon nucleus; also called the triple-alpha

reaction. thermal pulses The predicted upward spikes in the rate of helium fusion, occurring every few thousand years, that occur near the end of a low-mass star’s life. planetary nebula The glowing cloud of gas ejected from a low-mass star at the end of its life. white dwarfs The hot, compact corpses of low-mass stars, typically with a mass similar to that of the Sun compressed to a volume the size of Earth. supernova The explosion of a star. mass exchange (in close binary star systems) The process in which tidal forces cause matter to spill from one star to a companion star in a close binary system. 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 a binary star system. pulsar A neutron star from which we observe rapid pulses of radiation as it rotates. equivalence principle The fundamental starting point for general relativity, which states that the effects of gravity are exactly equivalent to the effects of acceleration. gravitational redshift A redshift caused by the fact that time runs slowly in gravitational fields. event horizon The boundary that marks the “point of no return” between a black hole and the outside universe; events that occur within the event horizon can have no influence on our observable universe.

singularity The place at the center of a black hole where, in principle, gravity crushes all matter to an infinitely tiny and dense point. supermassive black holes Giant black holes, with masses millions to billions of times that of our Sun, thought to reside in the centers of many galaxies and to power active galactic nuclei. virtual particles Particles that “pop” in and out of existence so rapidly that, according to the uncertainty principle, they cannot be directly detected....