The three core types
All optical telescopes do the same thing: gather light and bring it to a focus. How they achieve that divides them into three families.
Refractor
Uses a convex objective lens to bend incoming light to a focus. The simplest design — Galileo used one in 1609. Excellent for planets and double stars. Limited to smaller apertures due to chromatic aberration and lens weight. Best for beginners.
Reflector (Newtonian)
Uses a concave primary mirror to reflect light to a secondary mirror, then to an eyepiece at the side of the tube. No chromatic aberration. Scales to enormous apertures — all major ground-based observatories use reflectors. Invented by Isaac Newton in 1668.
Catadioptric
Combines lenses and mirrors (Schmidt-Cassegrain, Maksutov) for a compact, portable design with a long focal length. Popular for amateur astrophotography and planetary observing. Corrector plate at front reduces aberrations from the primary mirror.
Space telescopes: above the atmosphere
Earth's atmosphere blurs visible light, absorbs ultraviolet, X-rays and most infrared, and introduces thermal noise. Space telescopes escape all three limitations. The Hubble Space Telescope (launched 1990, still operating in 2026) demonstrated what a 2.4-metre mirror can achieve when freed from atmospheric blurring. The James Webb Space Telescope (launched 2021) extends Hubble's reach into the mid-infrared with a segmented 6.5-metre gold-coated beryllium mirror, able to see the earliest galaxies in the observable universe.
Because JWST observes in infrared, it can peer through dust clouds where stars are forming — and detect the light of galaxies at redshift z > 13, seen as they were less than 400 million years after the Big Bang. See our Webb deep field article for the latest record observations.
Beyond visible light
The visible spectrum is a tiny slice of electromagnetic radiation. Modern astronomy spans the full range: radio observatories like the ALMA array in the Atacama Desert image cold molecular clouds where stars form; X-ray telescopes like NASA's Chandra reveal superheated gas in galaxy clusters; and the LIGO/Virgo detectors don't use light at all — they detect gravitational waves, ripples in spacetime. Multi-messenger astronomy — combining light, gravitational waves, and neutrinos — is the frontier of the field.
To understand what telescopes find when they look at other star systems, see our guide on how we find exoplanets.