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MILKY WAY |
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PERSEUS ARM Not until 1951 were astronomers sure that the Milky Way is a spiral galaxy. In that year, American astronomer William Morgan 91906-94) realized from the brightness of the stars in the constellations of Perseus, Cassiopeia, and Cepheus that they must all be at about the same distance. The graph he plotted showed that they lay in a band 5,000 – 8,000 light yeas away. He had discovered the Perseus Arm, the outermost main spiral arm. Being so close to the edge, it is vital to our understanding of the Galaxy because there ate few bright stars or complicated structures behind it to clutter our view. Structure of the Perseus Arm The Perseus Arm is one of the Galaxy’s main arms, but instead
of wrapping itself all the way around the Galaxy, it is made up of a series of unconnected
patches of young stars and nebulas. It also contains numerous supernova remnants –
the corpses of dead stars – which gives it the feel of a stellar graveyard. |
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