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Ch 24 Galaxies Pt1&2

Vocabulary

TermDefinition
Hubble Classification Scheme galaxy classification method according to their appearance
Spiral Galaxy composed of a flattened, star-forming disk, which may have spiral arms & a galactic bulge
Central Bulge thick distribution of warm gas and stars around the galactic center
Spiral Arm material in a galaxy forming a pinwheel-shaped design, beginning near the galaxy's center
Barred-Spiral "SB" galaxy that has a central bar of material, with spiral arms beginning near its ends
Elliptical Galaxy type of galaxy that ranges from highly elongated (E7) to nearly circular (E0) in appearance
Galactic Disk flattened region of gas & dust with active star formation bisecting a spiral galaxy's halo
Lenticular Galaxy (S0 or SB0) between an elliptical and a spiral galaxy; has a disk but no spiral arms
Irregular Galaxy does not fit into any of the other major categories in the Hubble classification scheme
Magellanic Clouds two small irregular dwarf galaxies that are gravitationally bound to the Milky Way (satellites)
Dwarf Galaxy small galaxy containing a few million stars
Galactic Tuning Fork diagram of Hubble's classification scheme
Cepheid Variable variable star whose luminosity changes within a period of more than a single day
Tully-Fisher Relation determines the luminosity of a spiral galaxy from its rotational velocity and mass
Type I Supernova explosive death of a white dwarf accreting too much mass in a binary system
Type II Supernova explosive death of a high-mass star
Standard Candle object with a known luminosity, such as a supernova, which can be used in estimating astronomical distances
Local Group small galaxy cluster that includes the Milky Way
Galaxy Cluster collection of galaxies held together by their mutual gravitational attraction
Virgo Cluster large cluster of galaxies in the constellation Virgo neighboring the Local Group
Universal Recession shows that almost all galaxies are moving away from each other
Hubble Diagram plot of galactic recession velocity versus distance; evidence for an expanding universe
Hubble Flow universal recession described by the Hubble diagram and quantified by Hubble's Law
Hubble's Law states recessional velocity is directly proportional to its distance
Cosmological Redshift redshift of an object that is due only to the Hubble flow of the universe
Recession Velocity rate at which two objects are moving away from one another
Hubble's Constant relationship between recessional velocity & distance (slope) in Hubble's Law
Observable Universe current spherical region of the universe that can be seen because radiation has had time to reach the Earth since the beginning of cosmological expansion
Created by: john_bailey720
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