Mount Wilson Observatory Virtual Tour
ISI Interferometer

The Infrared Spatial Interferometer (ISI) is operated by the University of California at Berkeley. The ISI system consists of three 65-inch telescopes, all mounted in separate trailers to allow them to be spaced at different distances and angles from each other.

The ISI telescopes, spaced up to 85 meters apart, observe the sky at mid-infrared wavelengths and combine the starlight received in the individual telescopes. High-resolution images of red-giant and Mira-type variable stars can be constructed from the combined starlight. High-precision measurements of the positions of stars in the mid-infrared will also be instrumental in establishing more precise astronomical reference frames high-precision tracking of interplanetary spacecraft equipped with infrared lasers.

In 1994, scientists on the ISI team made observations of the impact of Comet Shoemaker-Levy 9 on Jupiter. The spectroscopic data they obtained revealed ammonia gas thrown high into the atmosphere of the giant planet as a consequence of the impact.

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