Reflecting telescope

An optical telescope that uses one or more curved mirrors to collect and focus light. Its primary mirror avoids the chromatic aberration produced by lenses.

Primary mirror: The main light-collecting mirror in a reflecting telescope. Its curvature gathers incoming light and brings it toward a focus.
Isaac Newton: An English mathematician and physicist who built an early successful reflecting telescope in 1668. His compact design established the Newtonian arrangement of primary and diagonal mirrors.
Refracting telescope: An optical telescope that uses lenses to collect and focus light. It forms images by refraction and can suffer chromatic aberration absent from a single-mirror reflector.
Large Binocular Telescope: An optical observatory in Arizona with two 8.4-meter primary mirrors mounted side by side. Its paired reflectors combine large light-collecting area with binocular observing modes.
Secondary mirror: A smaller mirror that redirects light from a primary mirror toward an observing or recording position. Its placement determines where the focused image can be accessed.
James Gregory: A Scottish mathematician who described a reflecting telescope design with a concave secondary mirror in 1663. His proposed layout preceded Newton’s working reflector but was not built by him.
Chromatic aberration: Color fringing caused when a lens focuses different wavelengths of light at different distances. A reflecting telescope’s mirror brings wavelengths to a common focus without this lens defect.
Hubble Space Telescope: A space observatory launched in 1990 that observes ultraviolet, visible, and near-infrared light. Its 2.4-meter primary mirror gathers light above Earth’s atmosphere.
Newtonian telescope: A reflecting telescope that uses a concave primary mirror and a flat diagonal secondary mirror. The diagonal secondary sends the image to a side-mounted eyepiece.
John Hadley: An English mathematician and instrument maker who built improved reflecting telescopes in the early eighteenth century. His practical instruments helped demonstrate that reflectors could rival refractors.

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