Galactic structure

absolute magnitudes apparent magnitude appears areas Astr average Blaauw blue stars bright brighter cent cepheids circular velocity clouds color components concentration curve density distribution density gradient derived determined diagram direction discussed disk distance Eggen emission equation estimate faint fainter Figure galactic center galactic latitude galactic plane Galaxy giants given globular clusters H n regions halo high-velocity stars Hyades hydrogen Ibid indicated interstellar gas investigations ionized kinematic km/sec longitude luminosity function magnetic field main sequence mean Milky number of stars objects observed obtained Oort optical orbits parallaxes Parenago parsecs planetary nebulae population proper motions radial velocities Rhijn rotation RR Lyrae variables Sandage solar motion space density space distribution spectral class spectral type spectroscopic spiral arms spiral structure stellar subdwarfs supergiants Table tion total mass values velocity dispersion velocity distribution weak-line Westerhout white dwarfs