DSST Astronomy notes 1

Has many stars concentrated toward the center bi3

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Has many stars concentrated toward the center (b.i.3) Sparse scattering of stars extends for great distances and merges into the void (b.i.4) Do not rotate as rapidly as spirals (b.i.5) Hard to measure total size (b.i.6) Have much greater size, mass, and luminosity than do the spirals c) A small number are classified as irregular (c.i.1) About 3% of the brightest galaxies in the northern sky (c.i.2) Show no trace of circular or rotational symmetry (c.i.3) Appearance is irregular and chaotic 151) Clusters of Galaxies - now regarded as fundamental condensations of matter in the universe a) Regular Clusters (a.i.1) Have spherical symmetry and show marked central concentration (a.i.2) Very rich clusters (a.i.3) Contain thousands of members (a.i.4) Resemble those of globular star clusters (a.i.5) Consist almost entirely of elliptical galaxies b) Irregular Clusters b.i)Sometimes called open clusters b.ii) Have more formless appearance b.iii) Possess little or no spherical symmetry or central concentration b.iv) Sometimes have sub-condensations b.v) Resemble loose swarms of small clusters b.vi) Contain all kinds of galaxies, spirals, elliptical, and irregulars b.vii) More numerous than regular clusters b.viii) Can be small groups or large c) Virgo Cluster is the closest cluster of galaxies to our Milky Way Galaxy c.i) Approximately 1,300 member galaxies c.ii) Part of the larger Local Super cluster 152) Local Group a) Comprises over 35 galaxies b) Two most massive – Milky Way and Andromeda 153) Intergalactic Space – considerable matter exists that is not associated with a galaxy or cluster a) Left over gas and dust b) Rapidly moving stars escape from galaxies and from star clusters c) Collisions or tidal interactions 154) Cosmogony – the theory about the origin and development of the universe a) Seeks to explain how the universe came to be 155) Cosmology – is the science of the universe, the universe as a whole a) and includes cosmogony b) Explain the composition of the universe and the laws that govern it 156) The Radial velocity of galaxies is the component of relative velocity that lies in the line of sight. Remember that velocity consists not only of speed, but also of direction.
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a.i) The radial velocity of a galaxy is its velocity in the line of sight, or in other words its speed straight towards you or away from you. a.ii) Evidence from the radial velocities of the galaxies acknowledges that the universe is expanding. The first radial velocities of galaxies were measured by V. M. Slipher at the Lowell Observatory. 157) The more distant a galaxy, the greater, in direct proportion, its speed of Recession as determined by the shift of its spectral lines to the longer (or red) wavelengths. a) By the 1930's, M.L. Humason and Edwin Hubble had begun to photograph spectra of fainter galaxies and found that in general, the fainter and smaller a galaxy appeared, the higher was its redshift. b)
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Has many stars concentrated toward the center bi3 Sparse...

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