PHY122 Vocab Part 1

PHY122 Vocab Part 1 - Chapter 12 Calibrated: the...

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Chapter 12 Calibrated: the establishment of the relationship between a parameter that is easily determined and a parameter that is more difficult to determine. For example, the periods of Cepheid variables have been calibrated to reveal absolute magnitudes, which can then be used to find distance. Thus astronomers say Cepheids have been calibrated as distance indicators. Variable stars: a star whose brightness changes periodically Cepheid variable star: variable star with a period of 60 days whose period of variation is related to luminosity Instability strip: the region of the H-R diagram in which stars are unstable to pulsation. A star passing through this strip becomes a variable star RR Lyrae varible star: variable star with period of from 12 to 24 hours, common in some globular clusters Period-luminosity relation: the relation between period of pulsation and intrinsic brightness among Cepheid variable stars Proper motions: the rate at which a star moves across the sky, measured in seconds of arc per year Shapley-Curtis debate: the 1920 debate between Harlow Shapley and Heber Curtis on the nature of spiral nebulae. Curtis argued that they are other galaxies, and Shapley argued that they are internal to our own galaxy Disk component: all material confined to the plane of the galaxy Kiloparsecs: a unit of distance equal to 1000 pc or 3260 ly Spiral arms: long spiral pattern in a disk galaxy composed of bright stars, star clusters, gas, and dust. Spiral arms extend from the center to the edge of the disk of spiral galaxies Spherical component: the part of the galaxy including all matter in a spherical distribution around the center (the halo and nuclear bulge) Nuclear bulge: the spherical cloud of stars that lies at the center of spiral galaxies Halo: the spherical region of a spiral galaxy, containing a thin scattering of stars, star clusters,
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PHY122 Vocab Part 1 - Chapter 12 Calibrated: the...

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