CHARA array, Optical telescope array on Mount Wilson, California, US

The CHARA array is an optical interferometer on Mount Wilson, California, made of six 1-metre telescopes arranged in a Y shape across a 400-metre circle. Light from each telescope travels through vacuum tubes to a 100-metre building, where a movable mirror combines the beams. The photograph shows one telescope's cylindrical building with ribbed grey metal panels and a domed roof with an upward-hinged shutter.

CHARA was founded in 1984, and planning for the array began in 1985 with National Science Foundation support. Construction started on 13 July 1996, funded by $6.3 million from the NSF matched by Georgia State University, which owns the facility. A $1.5 million Keck Foundation grant in 1998 added a sixth telescope to the planned five, and the array was completed in 2003.

The facility contributes to astronomical research by enabling direct measurements of star diameters, surface features, and binary star systems across the universe.

The six 1-metre telescopes stand on Mount Wilson in a Y-shaped layout across a 400-metre circle, with baselines between 34 and 331 metres; the beams are combined in a 100-metre building. The site is reached by a mountain road, and the array is used for about 50 nights per year through the NOAO peer-review system, so access follows that allocation rather than open visiting.

In 2024 a seventh, mobile telescope joined the six fixed ones, pushing the array's resolving power toward that of a roughly 600-metre mirror. The original six sit on a 400-metre circle in a Y shape, with baselines between 34 and 331 metres.