Description: A telescope is a device that collects photons (of visible light or other wavelengths) from distant objects and provides information (e.g. an image) about them to an observer. Early telescopes (from the beginning of the 17th century) used lenses as optical elements (see refracting telescope). Lenses are limited in how large they can be made, so in order to see fainter objects in greater detail with larger telescopes, mirrors (see reflecting telescope) were instead used to focus the light. The largest optical telescopes are reflecting telescopes. In the 20th century, telescopes for studying other regions of the electromagnetic spectrum were invented, so there now exist radio telescopes, infrared telescopes, X-ray telescopes, etc. Because celestial sources are faint, astronomers tend to build large aperture telescopes to collect more light and reach finer angular resolutions.

Related Terms:

• Electromagnetic Radiation
• Infrared Telescope
• Radio Telescope
• Reflecting Telescope
• Refracting Telescope
• Angular Resolution
• X-ray Telescope
• Lens
• Mirror

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".