Abstract
© 2009 American Institute of Physics, S-0031-9228-0903-220-7 Daniel Kleppner’s Reference Frame entitled “Hanbury Brown’s Steamroller” (PHYSICS TODAY, August 2008, page 8) provided much insight into the correlation of photon counts from separate detectors. However, more than just demonstrating an interesting physical phenomenon, the technique was important for astronomy. In combination with radiant fluxes at Earth’s surface, the angular diameters of 32 hot stars measured with the intensity interferometer near Narrabri, Australia,1 gave empirical absolute surface fluxes in erg cm–2 s–1 Hz–1 for the stars. With the UV flux measurements from the Orbiting Astronomical Observatory-2 and the longer-wavelength data from the ground, the angular diameters gave the stellar surface temperatures.2 Previously, astronomers depended on fitting flux distributions to imperfect model atmospheres.
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