List of largest optical telescopes historically

Telescopes have grown in size since they first appeared around 1608, and they have become important tools for exploring the universe. These instruments magnify distant views and gather light, which helps scientists study stars, planets, and other objects in space. Over the years, astronomers have built bigger and better telescopes to see even farther and more clearly.

The size of a telescope is often measured by the diameter of its main lens or mirror, called the aperture. A larger aperture can collect more light, allowing astronomers to see fainter and more distant objects. This list shows how telescope sizes have changed over time, highlighting the most important milestones in their development.

Different technologies have been used to build telescopes, each offering new ways to improve how we observe the cosmos. From early refracting telescopes that used lenses to modern reflecting telescopes that use mirrors, these advances have opened new windows to the universe. The growth in telescope size reflects humanity's ongoing quest to understand our place in the stars.

Telescopes

By overall aperture

The following list shows some of the largest single optical telescopes by the size of their main lens or mirror (aperture). The telescopes are listed in the order they were built, showing how they grew over time. However, the size of a telescope's main lens or mirror isn't the only thing that matters. For example, William Parsons, 3rd Earl of Rosse's 72-inch (1.8 m) reflecting telescope didn’t work as well as smaller telescopes that came later, because its mirror wasn’t as good.

By historical significance

This list shows important optical telescopes in the order they appeared in history. It highlights how technology improved over time, showing more than just the size of the main mirror. Each telescope on this list helped scientists see the stars and planets better than ever before.