Book contents
- Frontmatter
- Contents
- List of figures
- List of tables
- Preface
- Acknowledgments
- 1 Astronomy through the centuries
- 2 Electromagnetic radiation
- 3 Coordinate systems and charts
- 4 Gravity, celestial motions, and time
- 5 Telescopes
- 6 Detectors and statistics
- 7 Multiple telescope interferometry
- 8 Point-like and extended sources
- 9 Properties and distances of celestial objects
- 10 Absorption and scattering of photons
- 11 Spectra of electromagnetic radiation
- 12 Astronomy beyond photons
- Credits, further reading, and references
- Appendix: Units, symbols, and values
- Index
7 - Multiple telescope interferometry
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- List of figures
- List of tables
- Preface
- Acknowledgments
- 1 Astronomy through the centuries
- 2 Electromagnetic radiation
- 3 Coordinate systems and charts
- 4 Gravity, celestial motions, and time
- 5 Telescopes
- 6 Detectors and statistics
- 7 Multiple telescope interferometry
- 8 Point-like and extended sources
- 9 Properties and distances of celestial objects
- 10 Absorption and scattering of photons
- 11 Spectra of electromagnetic radiation
- 12 Astronomy beyond photons
- Credits, further reading, and references
- Appendix: Units, symbols, and values
- Index
Summary
What we learn in this chapter
Radio astronomers have learned to overcome the limitations of diffraction with interferometry, the use of two or more telescopes viewing the same source at the same time. The instantaneous beam of two telescopes is an interference fringe pattern on the sky. As the earth rotates, the pattern sweeps across a postulated point source yielding a time varying interference signal when the signals from the two telescopes are summed or multiplied. Simple examples show that two telescopes on the rotating earth can, in most cases, locate the position of a point source. Each brief two-telescope observation with a given baseline (telescope separation and relative orientation) can be described as a point on a two-dimensional plot (Fourier plane) of the x and yspatial frequencies. For each such point, the detected oscillatory signal yields a value of the complex visibility function V(b) which is one spatial Fourier component of the sky brightness distribution. Large arrays of telescopes making repeated observations as the earth rotates provide additional points in the Fourier plane and thus additional Fourier components. With sufficient coverage of the Fourier plane, the Fourier transform of V(b) yields a reasonable approximation of the true sky brightness function. This process is called aperture synthesis.
Interferometry dominates radio astronomy, e.g., the US VLA and the Australian AT arrays. The greatest antenna spacings yield the highest angular resolution. […]
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- Information
- Astronomy MethodsA Physical Approach to Astronomical Observations, pp. 175 - 217Publisher: Cambridge University PressPrint publication year: 2003