The scientific study of the stars and other objects in space is called astronomy. Astronomers observe the Universe using telescopes, which focus light from distant objects and make them clearer. Different types of telescope also reveal rays of light that are invisible to the human eye. On the ground, radio telescopes capture radio waves. Telescopes in space study rays that cannot pass through Earth’s atmosphere.
The Hale Telescope at Palomar Observatory in California, USA, was completed in 1948, and was the first giant telescope. It has a light-gathering mirror 508 cm (200 in) across. There are two types of telescope that study light. Reflecting telescopes capture light with a mirror, and refracting telescopes use a lens. All modern professional telescopes are reflectors.
Galileo was a physicist, mathematician, and an astronomer. In 1609 he built a telescope and became the first person to use one to look at the heavens. He saw mountains on the Moon, spots on the Sun, observed the phases of Venus, and discovered Jupiter’s four large moons. In later life, his support for the view of Copernicus that Earth and the planets circle round the Sun brought him into conflict with the Church.