Discovering Mount Wilson Chapter 12: The CHARA Array

Image caption: One of CHARA’s six connected telescopes, at sunset. 

Our series ‘Discovering Mount Wilson’ continues with Chapter 12 and the story of the newest viewing project on Mount Wilson, the CHARA Array, operated by the Center for High Angular Resolution Astronomy at Georgia State University (GSU). GSU chose Mount Wilson as the site for CHARA because of the exceptional ‘seeing conditions’ – much the same reason as founder George Ellery Hale initially chose the area more than a hundred years earlier. 

CHARA features an array of six telescopes, each with a one-meter diameter mirror to reflect light. They are spread across the mountain to increase the angular resolution of the array.  Light from each of the six telescopes is transported through newly installed fiber optics, to a special beam combining room. There the light from all six telescopes is combined by computer-controlled optics, and a computer turns the combined light into a synthetic image. This process, called interferometry, allows the array to have the same resolving power as a telescope with a 330-meter mirror, and an angular resolution of 200 micro-arcseconds. That’s the size of an astronaut footprint on the moon, as seen from Earth.

Founded in 1984 with initial support from the National Science Foundation (NSF), CHARA finally began construction on the array on July 13, 1996, with funding of $6.3 million from the NSF and matching funding from the university. In July 1998, GSU was awarded another $1.5 million by W.M. Keck Foundation, which allowed for a sixth telescope to be added to the previously planned five. With a gift of $574,000 from the David and Lucile Packard Foundation in 1998, funding was finalized. The full six-telescope CHARA Array was completed in 2003 and it propelled Mount Wilson back into the cutting edge of astrophysics.  As of today, CHARA has been awarded a grant of $2.5 million from NSF/MRI, along with $1.1 million from GSU, for the installation of a seventh telescope. Unlike the other six, this one will be portable, and will significantly enhance the capabilities of the CHARA Array.

Since its completion, CHARA has become the preeminent site for testing beam-combining technology, and is the largest instrument of its kind in the world.  The Array is applicable to problems in almost all areas of contemporary astronomy. It is particularly suited to stellar astrophysics, where it is used to measure the diameters and temperatures of stars, to image features such as spots and flares on their surfaces, and to map the orbits of close binary companions. Other projects range from detecting other planetary systems, imaging stars in process of formation, and studies of bright transient phenomena like novae.

For more information on this cutting-edge working research facility and the science that is emerging from it, visit the CHARA Array website.  

‘Discovering Mount Wilson’ returns on September 7, with Chapter 13. We hope you’ll check back for that post here  — and come see us up on the mountain, where ‘We Discovered Our Place in the Universe!’

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