 Astronomical optical interferometry has had to overcome a number of technical issues not shared by radio telescope interferometry . The short wavelengths of light necessitate extreme precision and stability of construction . For example , spatial resolution of 1 milliarcsecond requires 0 @.@ 5 µm stability in a 100 m baseline . Optical interferometric measurements require high sensitivity , low noise detectors that did not become available until the late 1990s . Astronomical " seeing " , the turbulence that causes stars to twinkle , introduces rapid , random phase changes in the incoming light , requiring kilohertz data collection rates to be faster than the rate of turbulence . Despite these technical difficulties , roughly a dozen astronomical optical interferometers are now in operation offering resolutions down to the fractional milliarcsecond range . Fig . 12 shows a movie assembled from aperture synthesis images of the Beta Lyrae system , a binary star system approximately 960 light @-@ years ( 290 parsecs ) away in the constellation Lyra , as observed by the CHARA array with the <unk> instrument . The brighter component is the primary star , or the mass donor . The fainter component is the thick disk surrounding the secondary star , or the mass gainer . The two components are separated by 1 milli @-@ arcsecond . Tidal distortions of the mass donor and the mass gainer are both clearly visible . 
