One of the six domes of the CHARA array appears shiny and new compared to the 150-foot solar telescope, on the left, and the 100-inch Hooker telescope, on the right. The two older telescopes have since been given a fresh coat of white paint. Photo: Elisa Webster

CHARA (Center for High Angular Resolution Astronomy)


Mount Wilson’s newest astronomical instruments are Georgia State University’s optical interferometric array of six telescopes. This facility, located here because of the exceptional seeing conditions, puts Mount Wilson back on the cutting edge of astrophysics. The full array was completed in 2004. Each telescope of the CHARA Array has a light-collecting mirror 1-meter in diameter. The telescopes are dispersed over the mountain to provide a two-dimensional layout that provides the resolving capability (but not the light collecting ability!) of a single telescope a fifth of a mile in diameter. Light from the individual telescopes is conveyed through vacuum tubes to a central Beam Synthesis Facility in which the six beams are combined together. When the paths of the individual beams are matched to an accuracy of less than one micron, after the light traverses distances of hundreds of meters, the Array then acts like a single coherent telescope for the purposes of achieving exceptionally high angular resolution. The Array is capable of resolving details as small as 200 micro-arcseconds, equivalent to the angular size of a nickel seen from a distance of 10,000 miles. In terms of the number and size of its individual telescopes, its ability to operate at visible and near infrared wavelengths, and its longest baselines of 330 meters, the CHARA Array is arguably the most powerful instrument of its kind in the world.

Science Objectives

The Array is applicable to problems in almost all areas of contemporary astronomy. It is particularly suited to stellar astrophysics where it will be used to measure the diameters, distances, masses, and luminosities of stars, as well as to image features such as spots and flares on their surfaces. Other projects range from detecting planetary systems, imaging stars in process of formation, and studies of bright transient phenomena like novae.

For more information on this amazing research facility and the science that is emerging from it, please go to the CHARA array homepage.


There you can find a video, Sizing up the Stars, that explains how interferometry works. Also on the mountain, next to the 100-inch telescope, there is a new exhibit hall that displays Albert Michelson’s original interferometer, used to get the first measurement of stars other than our Sun.  The exhibit hall reveals in detail how the light is combined in the new CHARA area.

One of the six CHARA telescopes, which use interferometry to explore the Universe. This technique of combining light from widely separated sources to achieve high resolution was pioneered at Mount Wilson. In 1920, Albert Michelson,the first American to win a Nobel Prize in physics, used an interferometer attached to the 100-inch telescope to measure the diameter of the red supergiant star Betelgeuse. This was the first measurement of a star other than our Sun.

A map of the mountaintop, showing the position of the six CHARA telescopes and the building where the light beams are combined. The array achieves the resolution of a mirror roughly a fifth of a mile in diameter.

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