SCI238 Lecture : L16 Milky Way.docx
9 Jul 2013
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Document Summary
It is a vast spiral galaxy, so named because of the spectacular spiral arms. Spiral arms are part of a fairly flat disk of stars surrounding a bright central bulge. 1000 light- years thick: our sun is located in the disk about 27,000 light-years from the galactic center. Clouds of interstellar gas and dust known collectively as the interstellar medium fill the galactic disk. The interstellar medium: what? looking out in some directions we see wide swaths of gas and dust: the interstellar medium. Hydrogen: by far the most common element in the ism; exists in three states: molecular: h2; neutral: hi; ionized: hii. Other elements also found in the three states: common molecules: co, nh3, h2o, hcn, oh, neutrals: ci, cai, nai, ions: cii, ciii, nii, oii, oiii, ovi, sii, siii. H2, ch, cc, cn, co, cs, oh, hcl, no, ns, sio, sis, so, ch+, so+ H2o, so2 , hco, c2h, hcn, h2s, sic2 , ocs, hno, hnc, hco+,
