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Michelson Scope

Astronomer using the Michelson interferometer attached to the 100-inch telescope at Mount Wilson Observatory

© The Huntington Library, San Marino, California

Science Bulletin Interferometry: Sizing Up the Stars

Sharper Images
The large girder in the exhibition is the Michelson Stellar Interferometer, a tool built by Albert Michelson (right) in the 1920s that boosted the power of an ordinary telescope. By aiming two light-gathering mirrors at the same star and then combining the two beams of light, an interferometer can create a high-resolution map of the star. Astronomers today also use interferometers to cancel out a star's light, thus revealing dimmer objects nearby, such as planets.


Interferometer mounted atop the Mt. Wilson 100-inch telescope

© The Huntington Library, San Marino, California

Combining light waves
Most telescopes use one large mirror to capture light from the skies. An interferometer creates a sharper image by combining light from two or more mirrors pointed at the same star. The Michelson Interferometer's two 12-inch mirrors could be moved up to 17 feet (five meters) apart, allowing it to resolve as much detail as a single, 17-foot-wide mirror.

interferometer diagram

Diagram of an Interferometer

Mt Wilson

Aerial photo of CHARA interferometer telescope array

© Eric Simison

The Future of Finding Planets
Armed with the latest interferometers, coronagraphs and other technologies, astronomers will soon capture the first images of faraway planets.

From Earth
Today's interferometers combine light from multiple telescopes, making it easier to look for planets. Georgia State University's CHARA telescope array on Mt. Wilson in southern California is powerful enough to see details on a nickel from 10,000 miles away. Light from six small telescopes is combined in the L-shaped "beam combining building."

Interferometer map

Interferometer map of the star γ-Cassiopeiaas measured by the CHARA array, revealing its bulging equator caused by extremely fast rotation. Our own, more spherical Sun is shown at lower right to scale.

Interferometer in Space

Artist's rendering of an interferometer in space. This is the concept for an ambitious new space observatory designed to see Earth-like planets around nearby stars.

© Navigator Program, NASA


From Space
To search for Earthlike planets, astronomers hope to launch an interferometer and a coronagraph into orbit where the images won't be distorted by Earth's atmosphere. These instruments could study light from an Earthlike planet to look for oxygen, water and other signs of life.

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