Optical telescopes are instruments used in astronomy to collect and focus light from distant celestial objects. They use lenses or mirrors to gather and magnify the light, allowing astronomers to observe and study stars, planets, galaxies, and other astronomical phenomena. Optical telescopes can come in various sizes and designs, such as refracting telescopes that use lenses to focus light, or reflecting telescopes that use mirrors. These instruments play a crucial role in advancing our understanding of the universe and have been fundamental in making many groundbreaking discoveries in astronomy.