Glossary term: Reflecting Telescope

Also known as mirror telescope or

Description: In a reflecting telescope or mirror telescope, the main optical element is a mirror, the "primary mirror", which gathers infalling light. Mirror telescopes are often characterized by primary mirror diameter, ranging from 10 centimeters for smaller amateur telescopes to eight meters for the largest solid mirrors used in professional telescopes. Still larger collecting areas can be obtained by combining several mirror segments, which then act in a way similar to that of a larger solid mirror. There are several types of mirror telescopes. For example, in a Newtonian telescope, the light coming from the primary mirror is reflected sideways by a smaller, flat mirror into an eyepiece or a camera. In a Cassegrain telescope, a smaller, convex secondary mirror reflects the light back through an opening in the main mirror.

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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".

Related Media

The two Keck telescopes seen from above. The domes are open and the telescopes' mirrors can be seen inside.

Keck Telescopes

Caption: The two Keck telescopes on Mauna Kea on the island of Hawai`i. These two telescopes are reflecting telescopes with primary mirrors 10m across.
Credit: NASA/JPL credit link

License: PD Public Domain icons

A telescope points to the sky where the Milky Way sits with mottled dark and light patches.

Learning Nights

Caption: Beneath the sprawling expanse of the night sky over Colombia's Tatacoa Desert, a telescope finds its alignment with the majestic galactic core, while a smartphone captures this cosmic encounter. This snapshot, taken on 9 June 2023 during an astronomy camp, epitomises the accessible beauty of celestial marvels. It showcases the mesmerising grandeur of the night sky, inviting both the casual stargazer and the passionate astronomer alike. The splendour of the Milky Way, elegantly captured through a mobile device, seamlessly bridges the gap between sophisticated equipment and the pure, profound joy of observing the stars.
Credit: Juan Pablo Botero LondoƱo/IAU OAE (CC BY 4.0)

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons