How Does a Telescope Work?

Optical telescopes come in two main types. Refracting telescopes use a large objective lens to bend (refract) incoming light to a focal point, where an eyepiece lens magnifies the image. Reflecting telescopes, pioneered by Isaac Newton, use a curved mirror to gather and focus light, avoiding chromatic aberration. Most large modern telescopes are reflectors. The key performance metric is aperture — the diameter of the primary mirror or lens — because a larger aperture collects more light, revealing fainter and more distant objects. The James Webb Space Telescope has a 6.5-metre segmented gold-coated mirror that observes in infrared, detecting light from galaxies over 13 billion light-years away.