Telescopes work by magnifying the light collected from distant objects. This is done by using a combination of lenses or mirrors. The most common type of telescope is the refracting telescope, which uses lenses to magnify the light. Refracting telescopes are typically used for observing objects that are relatively close, such as the Moon and planets.

Reflecting telescopes, on the other hand, use mirrors to magnify the light. Reflecting telescopes are typically used for observing objects that are very far away, such as stars and galaxies. This is because mirrors can be made much larger than lenses, which allows them to collect more light.

The largest telescopes in the world are reflecting telescopes. The largest optical telescope in the world is the Gran Telescopio Canarias, which is located in the Canary Islands. The Gran Telescopio Canarias has a primary mirror that is 10.4 meters (34 feet) in diameter. The largest radio telescope in the world is the Five-hundred-meter Aperture Spherical Telescope (FAST), which is located in China. FAST has a primary reflector that is 500 meters (1,640 feet) in diameter.

Telescopes have been used by astronomers for centuries to study the universe. They have allowed us to learn a great deal about the stars, planets, and galaxies that make up our universe. Telescopes have also helped us to understand our place in the universe.