interferometer in 2004. The world's largest physically connected telescope, the Square Kilometre Array (SKA), is planned to start operations in 2025. Astronomical observations Many astronomical objects are not only observable in visible light but also emit radiation at radio wavelengths. Besides observing energetic objects such as pulsars and quasars, radio telescopes are able to "image" most astronomical objects such as galaxies, nebulae, and even radio emissions from planets. See also Aperture synthesis Astropulse – distributed computing to search data tapes for primordial black holes, pulsars, and ETI List of astronomical observatories List of radio telescopes List of telescope types Search for extraterrestrial intelligence Telescope Radar telescope References Further reading Rohlfs, K., & Wilson, T. L. (2004). Tools of radio astronomy. Astronomy and astrophysics library. Berlin: Springer. Asimov, I. (1979). Isaac Asimov's Book of facts; Sky Watchers. New York: Grosset & Dunlap. pp. 390–399. American inventions Astronomical imaging Astronomical instruments