A so-called hypertelescope is an optical interferometric array, or set of telescopes, arranged in a large lens-shape, working together to resolve astronomical images at much higher angular resolutions than would be possible with each telescope alone. In fact, such a hypertelescope can allow an angular resolution approaching the resolution the telescope would have if its entire lens were as big as the distance across the array. For arrays with sizes in the kilometers or megameters, this can be very significant. However, angular resolution is not the only meaningful quality of telescopes, causing most astronomers to see the hypertelescope as a specialized instrument.
The hypertelescope uses a technique called aperture synthesis to simulate a giant telescope with an array of smaller telescopes. The techniques used to implement the hypertelescope and make sense of its data are interferometric techniques, measurement techniques that combine two or more data points to create a clearer picture. The entire field is called astronomical optical interferometry. Even kilometer-wide hypertelescopes can circumvent many of the problems with singular earth-based telescopes.
Hypertelescopes were first built in the mid-1970s, when they were used to accurately measure the precise positions and diameters of nearby stars. The distance between the two furthest constituent telescopes is called the baseline, which started off at around a few meters or feet, and now ranges up to about a kilometer (0.62 miles). Larger iterations of the hypertelescope are planned or in production now, including a space-based hypertelescope with its parts held in place by solar sails.
French hypertelescope pioneer Antoine Labeyrie has envisioned using hypertelescope arrays to image nearby exoplanets, or planets in foreign solar systems. Labeyrie and colleagues have shown how a technologically feasible hypertelescope could be used to detect surface features such as continents, seasons, and climates on worlds as far as 10 light-years away. This could be very useful for determining the presence or absence of microbial life. In the future, even larger hypertelescopes could be used to image extremely small or faint objects, such as neutron stars.