Interferometry is a technique pioneered by Albert A. Michelson in the 19th century. Optical interferometry, which has matured within the last two decades, combines the light of multiple telescopes so that precise measurements can be made, akin to what might be accomplished with a single, much larger telescope. It is the interaction of light waves, called interference, that makes this possible. Interference can be used to cancel out the glare of bright stars or to measure distances and angles accurately. The construction of the word partially illustrates this: interfere + measure = interfer-o-metry. At radio wavelengths of the electromagnetic spectrum, interferometry has been used for more than 50 years to measure the structure of distant galaxies.