Telescopie

Telescopie, or telescopy in English, is the practice of observing distant objects with a telescope. A telescope gathers light or other radiation and presents magnified images or spectra for visual inspection, measurement, or recording. It is a cornerstone of observational astronomy.

The invention of practical telescopes occurred in the early 17th century in Europe. Galileo Galilei popularized their use for astronomy, observing moons, the rings of Saturn, and the phases of Venus. The first successful reflecting telescope was built by Isaac Newton in 1668, and later improvements—such as achromatic lenses—reduced color distortion. From the 18th to 20th centuries, larger instruments expanded observable skies, and space-based telescopes began operating in the late 20th century to overcome atmospheric limits.

A telescope works by collecting light with an objective lens or mirror and forming an image inside an eyepiece or onto detectors. Key specifications include aperture, which governs light gathering and resolution, and focal length, which affects magnification. Image quality is limited by diffraction, optical errors, and atmospheric seeing. Main designs include refractors, reflectors, and catadioptric systems.

Telescopes operate across the electromagnetic spectrum, from optical to infrared, ultraviolet, and radio. They enable a broad range of activities, including astrometry, photometry, spectroscopy, and astrobiology research, as well as imaging for public and professional astronomy. Advancements such as adaptive optics, larger mirrors, and space-based platforms continue to enhance resolution and sensitivity.