<ul><li>Astronomers use 21cm radiation, emitted by hydrogen atoms, to map the structure of the Milky Way.</li><li>21cm radiation can travel through interstellar dust, allowing astronomers to study star-forming gas clouds and the shape of spiral arms of the galaxy.</li><li>By analyzing the redshift and blueshift of 21cm radiation, astronomers can determine the rotation speed of different regions of the Milky Way, providing insights into its dynamics and motion.</li><li>21cm radiation is also used to estimate the masses of distant galaxies by examining the neutral hydrogen gas clouds in those galaxies.</li></ul>

How Astronomers Make Deep Maps of the Milky Way

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