The clouds of Taurus-Auriga, indicated as the shaded area of Figure 1.1, have long been noted even in optical images. Figure 1.8 is a photograph from early last century by E. E. Barnard, covering a region of about 50 square degrees. Here one sees prominent dark lanes in the otherwise rich stellar field. Referring to this photograph in his 1927 atlas of the Milky Way, Barnard wrote
Very few regions of the sky are so remarkable as the Taurus region. Indeed, the photograph is one of the most important of the collection, and bears the strongest proof of the existence of obscuring matter in interstellar space.
Even more convincing - indeed, definitive - proof of interstellar dust was to come several years later, with J. Trumpler's demonstration of the progressive reddening of distant clusters.
The molecular gas accompanying the obscuring dust can be seen most readily in 12C16O, as shown in Figure 1.9. The Taurus-Auriga region covers a greater angular area than the Orion
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