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Last update: June 1, 2013

What Is an Astronomical Interferometer?

ESO’s Very Large Telescope Interferometer

Image description: VLTI (Very Large Telescope Interferometer), combining 4 fixed telescopes and 4 mobile telescopes. Image source: ESO (new window)

Principle of Astronomical Interferometry

An astronomical interferometer combines signals from multiple separate telescopes to achieve a resolution equivalent to that of a single telescope with a diameter equal to the maximum distance between the telescopes. The telescopes are often spaced several kilometers apart to maximize the resolution of images of very distant objects such as stars, quasars, black holes, or galaxies.

The signals are collected and directed to a central point where interference produces a high-resolution image, much more detailed than with a single telescope.

Interferometers also allow precise measurement of the distance between stars, which is crucial for understanding the structure of our galaxy.

Major Existing Interferometers

Here are the most powerful interferometers, ranked by capacity and location:

Comparison of Astronomical Interferometers
InterferometerAgency / ObservatoryNumber of TelescopesTelescope DiameterLocationComments
VLTIESO, Chile4 fixed + 4 mobile8.2 mParanal ObservatoryCombines several telescopes to achieve exceptional resolution
Keck InterferometerKeck Observatory, Hawaii210 mMauna KeaEnables precise observations of stars and exoplanets
LBT InterferometerMount Graham Observatory, Arizona28.4 mArizona, USABinational Italian-American observatory
CHARA ArrayGeorgia State University, USA61 mMount Wilson, GeorgiaExcellent for measuring stellar diameters and interstellar distances
MROIMagdalena Ridge Observatory, New Mexico10 (under construction)1.4 mNew Mexico, USAWill allow high-resolution imaging of multiple stars simultaneously

Scientific Applications

These interferometers allow the study of: stellar evolution, planet formation, binary interactions, galactic structure, and the detection of circumstellar disks. They are now an essential tool for astronomers seeking to push beyond the limits of single telescopes.

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