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46. 21-Centimeter Radio Astrophysics

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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References (certificates required)

Most important references are listed first.
  1. [1923] H.I. Ewen and E.M. Purcell, "Observation of a Line in the Galactic Radio Spectrum", Nature, 168, (1923)
  2. [1981] R. G. Lerner and G. L. Trigg, Encyclopedia of Physics, (Reading, MA, Addison-Wesley, 1981), "Radio Astronomy", pp. 41-42, Good introduction to radiometry by Arno Penzias
  3. Radio Astronomy of the Sun from "Radio Astronomy", 2nd Edition by John D. Kraus: 1986
  4. Hydrogen Line Emission and Galactic Structure from "Radio Astronomy", 2nd Edition by John D. Kraus: 1986
  5. [1960] I. Schlovsky, "Cosmic Radio Waves: Chapter 4", Harvard University Press, pp. 202-270, (1960), Provides a good treatment of the physics of the 21-cm hydrogen line
  6. [1968] D. Mihalas and J. Binney, Galactic Astronomy,(San Francisco,W.H. Freeman, 1968), "Galactic Rotation and the Spiral Structure of Our Galaxy",Chap. 8
  7. [1982] F. H. Shu, The Physical Universe, (Mill Valley, CA, University Science Books, 1982), "Our Galaxy: The Milky Way System", Chap. 12. This reference gives a clear description of the interpretation of 21cm spectra in terms of the rotation curve of the Galaxy.
  8. Particle Data Group: Astrophysical Constants and Parameters
  9. [1973] M.A. Tuve and S. Lundsager, "Velocity Structures in Hydrogen Profiles: A Sky Atlas of Neutral Hydrogen Emission", Carnegie Institution ofWashington Publication, no. 630, (1973). The data in Appendix B are particularly useful for verifying the quality of your own data using our much lower resolution SRT.

    10. Selected Resources

    1. Google Sky
    2. Solar Noon Calculator
    3. NOAA Solar Position Calculator
    4. Wikipedia Entry on the Milky Way Galaxy
    5. Cambridge University Press Handbook of Space Astronomy and Astrophysics
    6. Marshall Space Flight Center - Solar Research Page
    7. Excerts from "Radio Astronomy", 2nd Edition by John D. Kraus: 1986
      1. Antennas
      2. Recievers
    8. UC San Diego Center for Astrophysics - Prof. Gene Smith's Milky Way Tutorial
    9. History of Radio Astronomy at MIT
    Small Radio Telescope Engineering Resources
    1. Haystack Observatory's SRT Website This is a very important site for students to investigate. Detailed block diagrams and schematics of the 21-cm receiver, mount and ground controller are available here.
    2. SAMI Antenna Installation Manual
    3. Electronic Noise Calibration System for the SRT
    4. American Radio Relay League
    5. 6.661 Receivers, Antennas, and Signals, Spring 2003
    6. FCC Radio Spectrum Frequency Allocation Chart
site maintained by bil with thanks to p. ragsdale 2005