Skip to main content Accessibility help
  • Print publication year: 2012
  • Online publication date: December 2012

11 - Optical interferometry

from Part III - Observing through the atmosphere



Less than 300 years after Galilei's first telescope observations of celestial objects, Fizeau (1868) suggested a way to improve the measurement of stellar diameters by masking the telescope aperture with two small sub-apertures. Light passing through these sub-apertures would then interfere in the telescope focal plane. The first successful measurement using this principle was performed on Mt. Wilson in 1920 by Michelson and Pease (1921) who determined the diameter of α Orionis to be 0.047 arcsec. This was at a time when the smallest diameter that could be measured with a full aperture was about 1 arcsec, equivalent to the angular resolution of the telescope when observing through atmospheric turbulence.

Although the measurement of a stellar diameter is not the same as an image, the dramatic increase in angular resolution sparked enough interest in the new method that it was soon understood how such contrast measurements with different pairs of sub-apertures – different in separation and orientation – can be combined to form a high-resolution image not only of stars but of any type of object.

However, due to insurmountable technical problems with the mechanical stability at larger separations of the sub-apertures, optical interferometry was abandoned in the late 1920s. It was not until 1974 that Labeyrie (1975) was able to combine the light from two independent telescopes at the Observatoire de la Côte d'Azur, demonstrating that optical interferometry was feasible.

While angular resolution increases linearly with the telescope diameter when eliminating atmospheric turbulence with adaptive optics, even today's largest telescopes cannot resolve features on the surface of individual stars. The diffraction limit is still so much larger than a star’s disk that their images in the telescope focal plane are indistinguishable from point sources. For example, an angular resolution of 50 milliarcseconds (mas) on an 8-m telescope is only just about the angular size of Betelgeuse.

Related content

Powered by UNSILO
Baldwin, J. E., Beckett, M. G., Boysen, R. C., et al. (1996). The first images from an optical aperture synthesis array: mapping of Capella with COAST at two epochs. A&A, 306, L13.
Bridle, A. H. and Schwab, F. R. (1999). Bandwidth and time-average smearing. ASP Conf. Ser., 180, 371.
Colavita, M.M. and Wizinowich, P. (2002). Keck Interferometer update. Proc. SPIE, 4838, 79.
Colavita, M. M., Wallace, J. K., Hines, B. E., et al. (1999). The Palomar Testbed Interferometer. AJ, 510, 505.
Colavita, M. M., Akeson, R., Wizinowich, P., et al. (2003). Observations of DG Tauri with the Keck Interferometer, AJ, 592, L83.
Delplancke, F., Derie, F., Lévêque, S., et al. (2006). PRIMA for the VLTI: a status report. Proc. SPIE, 6268, 62680U-1.
Domiciano, de Souza A., Kervella, P., Jankov, S., et al. (2003). The spinning-top Be star Achernar from VLTI-VINCI. A&A, 407, L47.
Eisenhauer, F., Perrin, G., Brandner, W., et al. (2008). GRAVITY: getting to the event horizon of Sgr A*. Proc. SPIE, 7013, 70132A-1.
Fizeau, H. (1868). Prix Borodin: rapport sur le concours de l'année 1867. C. R. Acad. Sci., 66, 932.
Glindemann, A. (2011). Principles of Stellar Interferometry. Berlin: Springer-Verlag.
Glindemann, A., Argomedo, J., Amestica, R., et al. (2002). The VLTI – a status report. Proc. SPIE, 4838, 89.
Goodman, J. W. (1985). Statistical Optics. New York, NY: J. Wiley & Sons.
Hale, D. D. S., Bester, M., Danchi, W. C., et al. (2000). The Berkeley Infrared Spatial Interferometer: a heterodyne stellar interferometer for the mid-infrared. AJ, 537, 998.
Hanbury Brown, R. and Twiss, R. Q. (1956a). Correlation between photons in two coherent beams of light. Nature, 177, 27.
Hanbury Brown, R. and Twiss, R. Q. (1956b). A test of a new type of stellar interferometer on Sirius. Nature, 178, 1046.
Hill, J. M., Green, R. F., and Slagle, J. H. (2006). The Large Binocular Telescope. Proc. SPIE, 6267, 1.
Johnson, M. A., Betz, A. L., and Townes, C. H. (1974). 10-μm heterodyne stellar interferometer. Phys. Rev. Lett., 33, 1617.
Kervella, P., Thévenin, F., Ségransan, D., et al. (2003). The diameters of α Centauri A and B. A&A, 404, 1087.
Labeyrie, A. (1975). Interference fringes obtained with Vega with two optical telescopes. AJ, 196, L71.
Lane, B. F., Colavita, M. M., Boden, A. F., and Lawson, P. R. (2000). Palomar Testbed Interferometer – update. Proc. SPIE, 4006, 453.
Launhardt, R., Henning, T., Queloz, D., et al. (2008). The ESPRI Project: astrometric exoplanet search with PRIMA. Proc. SPIE, 7013, 70132I-1.
Lopez, B., Antonelli, P., Wolf, S., et al. (2008). MATISSE: perspective of imaging in the mid infrared at the VLTI. Proc. SPIE, 7013, 70132B-1.
Mandel, L. (1963). Fluctuations of light beams. In Progress in Optics II, ed. E., Wolf. Amsterdam: North-Holland, p. 181.
Michelson, A. A. and Pease, F. G. (1921). Measurement of the diameter of α Orionis with the interferometer. AJ, 53, 249.
Muterspaugh, M. W., Lane, B. F., and Konacki, M. (2006). Scientific results from highprecision astrometry at the Palomar Testbed Interferometer. Proc. SPIE, 6268, 62680F-1.
Shao, M. and Colavita, M.M. (1992). Potential of long-baseline infrared interferometry for narrow-angle astrometry. A&A, 262, 353.
Shao, M. and Staelin, D. H. (1977). Long-baseline optical interferometer for astrometry. J. Opt. Soc. Am., 67, 81.
Shao, M. and Staelin, D. H. (1980). First fringe measurements with a phase-tracking stellar interferometer. Appl. Opt., 19, 1519.
Thomson, A. R.,Moran, J. M., and Swenson, G.W. Jr., (1986). Interferometry and Synthesis in Radio Astronomy. New York, NY: J. Wiley & Sons.