1900 BC  early mirrors
1621 AD  Willebrord Snell's law of refraction states
         N1sin(1) = N2 sin(2)
1650     Francesco Grimaldi observes bands of light
         within the shadow of a rod illuminated by a
         small source.
1665     Isaac Newton shows that white light is
composed of many colors using a prism.
1801-1803  Thomas Young's wave theory of light.
1919     20 ft stellar interferometer built by Michelson
         measured diameter of Betelgeuse in 1920 at
         0.047 arc second.

The human eye sees 1 arc minute, a 6 inch scope sees 1
arc second.  The largest moons of Jupiter appear 1 arc
second in diameter from earth, Sirius 0.007 arc second.

The Twin Keck 85 meter baseline can now measure
0.003 arc second.  The CHARA array on Mount
Wilson has 6 scopes with a 350 meter maximum
baseline, and can measure 0.005 arc second.  The VLTI
in Chile has a 200 meter baseline capable of 0.001 arc