A telescope is an instrument that gathers and magnifies light from distant objects. It does two things: it collects more light than the human eye can, and it resolves finer detail. The bigger the aperture, the more light it collects and the sharper the image. That is why astronomers keep building larger telescopes.

There are two main types. A refracting telescope uses lenses to focus light. A reflecting telescope uses mirrors. Most large telescopes today are reflectors, because mirrors can be made much larger than lenses and do not suffer from chromatic aberration. Radio telescopes use dishes to collect radio waves. X-ray telescopes use nested mirrors to focus high-energy radiation. Each type is designed for a different wavelength.

Telescopes are time machines. When you look at a star, you see it as it was years ago. When you look at a galaxy, you see it as it was millions of years ago. The farther the telescope can see, the farther back in time it looks. The James Webb Space Telescope sees galaxies that formed just a few hundred million years after the Big Bang.

The telescope is one of the most important inventions in human history. It changed our place in the universe, and it continues to reveal new wonders.