In the 1500s Copernicus worked out that the planets revolved around the Sun. His views went against the teachings of the Church, so he did not publish his theory until he was lying on his deathbed in 1543. Planet pioneers Copernicus knew about the five planets nearest Earth. He spent hours observing Mars and tried to prove that the channels he saw on the planet were in fact canals dug by intelligent beings. Today's telescopes Galileo's telescope used lenses to collect light.
Modern telescopes use mirrors.
The Keck reflector in Hawaii uses 36 joined mirrors forming a reflective surface 10m across. The Hubble Space Telescope was launched in 1990. Its mirror is powerful enough to see light from a torch 400,000km away. In 1993 a fault in Hubble's mirror was repaired in orbit by astronauts. Voyager Space probes have been sent into orbit to collect information about our solar system.