The Milky Way divides the celestial sphere into two halves. To the naked eye it appears as a milky-white band, stretching across the starry heavens, joining up to form a circle around the northern and southern skies (Fig. 1.1). About 400 years before the starting date of our calendar, the Greek philosopher Democritus concluded: “the Milky Way consists of very many small stars, close together, which are all glowing, and which, because of their density, combine their light.” As Democritus had no telescope, he was unable to know that this was true, but could only suspect it. It was two thousand years before it was learnt that his suspicions were correct. For this, the telescope had first to be invented.
KeywordsFormaldehyde Dust Helium Carbon Monoxide
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