On a clear night, you can see thousands of stars twinkling above Earth. Long ago, people thought they knew everything about the sky.
Then, in 1608, a Dutch lens maker changed that. He put two glass lenses into a metal tube. The device made faraway objects seem close. It was later named a telescope. Scientists pointed the new device at the sky. They found new stars, planets, and moons. They also found proof that the Sun does not go around Earth, as most people then believed. Instead, Earth orbits the Sun, spinning as it goes.
Telescopes have improved since then. We now know that Earth is tiny, compared to the universe. Our home is a little dot in the Milky Way galaxy. And the Milky Way is only one of billions of galaxies.
Astronomers can look far out into the universe. However, humans haven’t yet learned how to travel to deep space. Until we do, telescopes are our window on the cosmos.
