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A simple two-element optical interferometer. Light from two small telescopes (shown as lenses) is combined using beam splitters at detectors 1, 2, 3 and 4.The elements create a 1/4 wave delay in the light, allowing the phase and amplitude of the interference visibility to be measured, thus giving information about the shape of the light source.
Along with the four 8.2-metre (320 in) unit telescopes, four mobile 1.8-metre auxiliary telescopes (ATs) were included in the overall VLT concept to form the Very Large Telescope Interferometer (VLTI). The ATs can move between 30 different stations, and at present, the telescopes can form groups of two or three for interferometry.
Aperture masking interferometry (or Sparse aperture masking) is a form of speckle interferometry, that allows diffraction limited imaging from ground-based telescopes (like the Keck Telescope and the Very Large Telescope), and is a high contrast imaging mode on the James Webb Space Telescope.
Figure 1. The light path through a Michelson interferometer.The two light rays with a common source combine at the half-silvered mirror to reach the detector. They may either interfere constructively (strengthening in intensity) if their light waves arrive in phase, or interfere destructively (weakening in intensity) if they arrive out of phase, depending on the exact distances between the ...
Three radio telescope receivers. A minimum of three antennas are required for closure phase measurements. In the simplest case, with three antennas in a line separated by the distances a 1 and a 2 shown in diagram at the right. The radio signals received are recorded onto magnetic tapes and sent to a laboratory such as the Very Long Baseline Array.
The distance between the radio telescopes is then calculated using the time difference between the arrivals of the radio signal at different telescopes. This allows observations of an object that are made simultaneously by many radio telescopes to be combined, emulating a telescope with a size equal to the maximum separation between the telescopes.
The most commonly used of these techniques are shift-and-add and interlacing. Drizzle was originally developed to combine the dithered images of the Hubble Deep Field North and has since been widely used for the combination of dithered images from both HST's cameras and those on other telescopes. Drizzle has the versatility of shift-and-add ...
Modern image processing techniques including deconvolution of the point spread function allow resolution of binaries with even less angular separation. Using a small-angle approximation , the angular resolution may be converted into a spatial resolution , Δ ℓ , by multiplication of the angle (in radians) with the distance to the object.