= Solution
Edge-on, the bright <thin galactic disk> forms a narrow band, with a central bulge protruding above and below it and a thinner gas-and-dust lane along the midplane. Young stars and <H II regions> occupy a vertical scale of a few tenths of a kiloparsec or less; a broader old <thick disk> has scale of order a kiloparsec. These are approximate scale heights, not sharp boundaries. The old <stellar halo> and <globular clusters> form a much larger, low-surface-brightness spheroidal component, extending to many tens of kiloparsecs or more. The <dark matter halo> is inferred dynamically rather than directly visible in such a sketch. The preceding figure is a structural diagram, not an external photograph or a reconstruction of a particular survey.
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