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Galileo made his telescope by placing a piece of glass called a lens at one end of a long, narrow tube. A telescope like this is not very powerful, so the view of objects in the sky is not sharp. And the lens tends to introduce false colors.
Late in the seventeenth century, Isaac Newton, dissatisfied with Galileo's spyglass-type of design, invented the reflector telescope. Newton's design used a curved mirror to gather light coming into the tube, providing sharper images of the stars and planets, without the color distortion of the earlier telescope.
The astronomer William Herschel, who discovered the planet Uranus in 1781, built the largest reflecting telescopes of his day. He used these instruments to
discover new moons around Saturn, distant double stars, and "island universes" -- what we now call galaxies.
Astronomers found that they could use special instruments to see ultraviolet and infrared light, as well as radio waves, coming from objects in space. These new ways of looking at the heavens showed us things that our eyes could not see.
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| The Hubble Space Telescope |
By the twentieth century, large observatories were being built all over the world and astronomers were making many discoveries. But Earth's atmosphere interferes with viewing. The Hubble Space Telescope orbits Earth, above our atmosphere.
But telescopes have limits and we wanted to know more. As technology developed, NASA sent spacecraft to our Moon .... and then to other planets.
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