Which scientist used telescopes for astronomy?

• A. Galileo Galilei
• B. Nicolaus Copernicus
• C. Tycho Brahe
• D. Johannes Kepler

Answer: (A)

Using a telescope opened a window to the universe beyond what the naked eye could see. Galileo Galilei is the scientist most famous for applying the telescope to astronomical study. With a telescope, he observed the Moon's rugged surface, moons orbiting Jupiter, the phases of Venus, and sunspots. These observations provided clear evidence that not everything revolves around Earth and that celestial objects can change over time, challenging the view of a perfect, unchanging sky. Copernicus proposed a sun-centered solar system but did not base his ideas on telescope observations. Tycho Brahe relied on extremely precise naked-eye measurements, not telescopic data. Johannes Kepler used Brahe’s data and made key advances in planetary motion and optics, but the notable use of a telescope in astronomy is most closely associated with Galileo.