How does the VLT Interferometer (VLTI) work?
The power of the VLT Interferometer does not come from adding the light beams from the individual telescopes to gather more light. Instead, the light waves are made to interfere with each other to produce patterns of light and dark fringes, a little like the way ripples on water can combine to produce either bigger waves or cancel to produce calm water. This technique is called interferometry. The fringes give us information about the structure of the observed object, but they are not an image of it. If an image is needed, it must be reconstructed by mathematically combining the information from many sets of fringes. However, many important scientific questions can be answered without making an image of an object. For the interferometry to work, the light waves must be combined very precisely using a complex system of mirrors in underground tunnels. The paths along which the light travels must be kept accurate to a fraction of the wavelength of the light, to control the phase of the wa
