What instrument did Galileo improve for astronomical observation?

Galileo improved the telescope for astronomical observation.

The telescope was invented in the Netherlands around 1608, but Galileo learned of the device in 1609 and built improved versions himself. His early instruments used a convex objective lens and a concave eyepiece, producing an upright, magnified image. Within months, he had increased their magnifying power far beyond the earliest spyglasses.

Galileo’s telescope transformed astronomy because it revealed details invisible to the naked eye. He observed mountains and craters on the Moon, countless stars in the Milky Way, the phases of Venus, sunspots, and four moons orbiting Jupiter. These observations challenged the traditional idea that the heavens were perfect and unchanging.

A common mix-up is crediting Galileo with inventing the telescope. He did not invent it, but he was among the first to develop it systematically for scientific observation and to publish major discoveries made with it.