A telescope is an optical instrument that makes distant objects appear magnified by collecting and focusing light. The first telescopes were simple refracting telescopes, which used lenses to magnify objects. Reflecting telescopes, which use mirrors to collect and focus light, were developed in the 17th century and are now the most common type of telescope.There are four major types of modern astronomical telescopes: refractors, reflectors, catadioptric, and radio telescopes. Refracting telescopes use lenses to gather and focus light. Reflecting telescopes use mirrors to do the same thing. Catadioptric telescopes combine both lenses and mirrors in a single design. Radio telescopes detect electromagnetic radiation emitted by astronomical objects at radio wavelengths.The James Webb Space Telescope (JWST) is a space telescope that will be launched in 2021. It is designed to study the early universe and observe distant galaxies. The Hubble Space Telescope (HST) is a space telescope that was launched in 1990. It is best known for its images of galaxies and nebulae. The Atacama Large Millimeter Array (ALMA) is a radio telescope array located in Chile. It is the largest astronomical project in existence.