Glossary term: Lens

Description: A lens is an optical device that, due to refraction, bends light so that it either focuses or disperses. Lenses are typically made from glass, plastic, or some other transparent material. Convex lenses focus light, drawing a parallel beam of light together to a point. Concave lenses spread a parallel beam of light so that it appears to originate from a point.

Lenses are the main components in refracting telescopes as well as binoculars. Even if an astronomical telescope is a reflecting telescope (one that uses mirrors to focus light), it is likely that the cameras and spectrographs attached to the telescope will use one or more lenses.

A massive object can be referred to as a "gravitational lens" when it induces optical distortion in the image of another background object. This distortion is due to bending of light from the background object due to the gravity of the massive foreground object; this phenomenon is referred to as gravitational lensing.

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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".