Measurement of the Doppler spectrum of interstellar atomic hydrogen and the dynamics of the galactic rotation. A 2.5-meter computer-controlled alt-azimuth parabolic dish antenna, located on a roof of MIT, is used with a heterodyne measurement chain and digital correlator to observe the Doppler spectrum of the 21-cm hyperfine line of interstellar atomic hydrogen in various directions along the Milky Way. Features of the spiral-arm structure of the Galaxy are deduced from the measured radial velocities of the HI clouds in the galactic disc.
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21-cm Radio Astrophysics lab.