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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.

Student Wiki: 21-Cm Radio Astrophysics

Download Lab Guide in PDF format

Live camera:

Other Manuals

Experiment Software

The SRT server daemon should already be running on the computer jlab-24 in 36. If not, contact the staff.

Here are the files necessary to start the SRT user interface from your own computer (right-click and save as):

Here are the Java source files used to create the .jar file (you don't need these unless you're really interested in how the program works): Download

Other Resources

MATLAB Parsers for the .rad files produced by the SRT software.

Parser 1 takes a .rad file and outputs an array of data structures, where each member of the array is a scan. Parser 2 takes a .rad file and outputs a large matrix where each row is a scan.

JAVA Parser for the .rad files; can plot scans and do some limited data analysis.

Previous incarnations of User's Manuals for the SRT. Still useful but some parts may be out of date.

Software Radio. Litster's notes of how the new SRT radio works: SoftwareRadio.pdf (also relevant to the old SRT).

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. [1954] H.C. Van de Hulst, "The Spiral Structure of the Outer Part of the Galactic System Derived from the Hydrogen Emission at 21cm Wave Length", Bulletin of the Astronomical Institutes of the Netherlands, Vol. 12, Number 452, (1954)
  11. [1969] F. J. Kerr, in "The Large Scale Distribution of Hydrogen in the Galaxy", Annu. Rev. Astro. Astrophys. (1969)
  12. Download Haystack Radio Telescope User's Manual (pdf)
  13. Download 2010 Users Manual Supplement

  14. 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 there.
      An updated technical discussion of the operation of the SRT is available here (pdf).
    2. SAMI Antenna Installation Manual
    3. Electronic Noise Calibration System for the SRT (pdf).
      There is also a copy of the report on this computer.
    4. American Radio Relay League
    5. 6.661 Receivers, Antennas, and Signals, Spring 2003
    6. FCC Radio Spectrum Frequency Allocation Chart
site maintained by the Junior Lab Staff