What instrument did Galileo improve to observe the heavens?

Galileo improved the telescope to observe the heavens. He did not invent the first telescope, but after learning of the new Dutch instrument in 1609, he constructed and refined his own versions for astronomical observation.

Galileo’s improved telescopes offered much greater magnification and allowed him to study the Moon’s rugged surface, the phases of Venus, sunspots, and the Milky Way’s countless faint stars. In January 1610, he used a telescope with roughly 20-power magnification to observe four moons orbiting Jupiter.

These observations challenged the traditional belief that the heavens were perfect and unchanging and that every celestial object revolved around Earth. The telescope was an optical instrument using lenses, unlike a sextant, which measures angles, or a microscope, which is designed for nearby small objects. Galileo’s work helped turn the telescope into a scientific research tool.