Mount Wilson Observatory - Interferometry

Interferometry

The extremely steady air over Mount Wilson is well suited to interferometry, the use of multiple viewing points to increase resolution enough to allow for the direct measurement of the size of details such as star diameters. Michelson performed the first measurements of other stars in the history of astronomical interferometry on the Hooker telescope in 1919.

The Infrared Spatial Interferometer (ISI) is an array of three 65 inches (1.7 m) telescopes operating in the mid-infrared. The telescopes are fully mobile and their current site on Mount Wilson allows for placements as far as 70 m apart, giving the resolution of a telescope of that diameter. The signals are converted to radio frequencies through heterodyne circuits and then combined electronically using techniques copied from radio astronomy. ISI is run by an arm of the University of California, Berkeley. The longest (70m) baseline provides a resolution of 0.003 arcsec at 11 micrometers. On July 9, 2003, ISI recorded the first closure phase aperture synthesis measurements in the mid infrared.

The Center for High Angular Resolution Astronomy (CHARA) array is an interferometer formed from six 1 m (40-inch) telescopes arranged along three axes with a maximum separation length of 330 m. The light beams travel through vacuum tubes and are combined optically, requiring a building 100 meters long with movable mirrors to keep the light in phase as the earth rotates. CHARA is operated by the Georgia State University and began scientific use in 2002 and began "routine operations" in early 2004. In infrared the integrated image can resolve down to 0.0005 arcseconds. As of 2005, four of the six telescopes have been commissioned for interferometric observations.

These and other astronomical interferometers are included in the List of astronomical interferometers at visible and infrared wavelengths. The history of the development of these instruments is given in History of astronomical interferometry.