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# Telescopes

Have you ever looked through a telescope at the night sky? Stars, moons, and planets become even more brilliant and distinct. Glancing up at the sky with our own eyes, we see only the tiniest fraction of the light that blazes from other stars and galaxies. Telescopes help us to focus that light and allow us to see more than we ever imagined was out there.

The first optical telescope was invented in the 1570's and consisted of one concave lens and one convex lens fitted inside a tube. The lenses refracted light and magnified objects two to four times. By 1609, the astronomer Galileo had developed a better model of the refracting telescope that magnified by about 20 times. With this instrument he saw that the moon, which many people thought was perfectly smooth, was actually covered with craters, peaks, and valleys! He also dicovered four of Jupiter's moons. Astronomy would never be the same.

The magnification of refracting telescopes could only be increased by lengthening the tube that contained the lenses. Thus, the father into space people wanted to see, the longer the telescope had to be. In 1671, Sir Isaac Newton invented a reflecting telescope, a vast improvement over the refracting model. Reflecting telescopes contain a parabolic mirror that reflects all the light that hits it back through a single point, the focal point. From the focal point, the concentrated light travels up the tube to a flat mirror that deflects it into the eyepiece. The length of the tube can be considerably shorter than that of a refracting telescope.

This reflecting technology has been incorporated into amazing machines like the Hubble Space Telescope. Hubble orbits the Earth on a satellite, and the view it gives us is undistorted by the Earth's atmosphere. The telescope weighs 12 tons, and its parabolic mirror is eight feet in diameter. Hubble has given us pictures of comets, galaxies, black holes, and of the birth of stars. Yet our wonder at these sights could not surpass the wonder Galileo must have felt when he looked through his own small telescope at the moon for the first time in human history.

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