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Why did the invention of the telescope change astronomy?

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Astronomy Hubble Space Telescope, photographed by the space shuttle Discovery.

The invention of the telescope fundamentally transformed astronomy by allowing scientists to observe celestial phenomena that were previously invisible to the naked eye. By collecting and focusing significantly more light than the human pupil, telescopes enabled the detection of fainter and more distant objects, turning the field into an observational science.12

When Galileo Galilei first applied the telescope to the heavens in the early 17th century, his discoveries provided critical evidence that challenged traditional cosmological models. Key impacts included:13

Challenging Aristotelian views: Observations of a jagged, mountainous Moon and sunspots on the Sun refuted the belief that celestial bodies were perfect and immutable.435
Supporting Heliocentrism: The discovery of Jupiter’s satellites proved that not all bodies orbit Earth, while the phases of Venus provided direct evidence that it orbits the Sun.435

Since then, the development of increasingly powerful optical and non-optical telescopes has remained the most vital tool for investigating the universe, enabling modern understanding of the solar system, the Milky Way Galaxy, and beyond.1