How Does A Telescope Work?
Through a telescope the famous Orion nebular can be seen in great detail. And the Andromeda galaxy is a
Telescopes are an incredible invention. They allow us to look into outer space and see the planets and stars so clearly that they seem close enough to touch. But how did they evolve?The first telescope was invented in 1608 by a Dutch eyeglass maker named Hans Lippershey. However, it wasn't until 1610 that the Italian astronomer Galileo Galilei (1564-1642), first used one to look into space.Though Galileo's first attempts at building a telescope were very crude, he was able to see craters and mountains on the Moon and also Jupiter's four largest moons circling the planet.Telescopes remained very much the same until 1671 when the British scientist Sir Isaac Newton (1642-1727) realised that a mirror could be used instead of a lens to collect the light.In 1672 a French science teacher Laurent Cassegrain improved upon Newton's design.Galileo's telescope was what is known as a refracting telescope.Newton's telescope is called a reflecting telescope.And Cassegrain gave his name to the Cassegrain telescope. So how does a Telescope work?A refracting telescope is a long tube with a convex lens at one end and an eyepiece at the other. Light comes in through the convex lens and is condensed or refracted toward the eyepiece. There the image is magnified.A reflecting telescope uses a curved or concave primary mirror at the rear of the telescope. Light is collected by the mirror and is reflected back up the telescope tube until it reaches a secondary mirror set at a 45º angle. The image is then reflected out through the side of the telescope where it passes through a concave lens or eyepiece.Cassegrain's telescope is similar to Newton's but it uses a convex mirror to reflect the image back down the tube to come out through a hole in the centre of the primary mirror, where it is received in the eyepiece. The benefit of Newton's and Cassegrain's telescope compared to Galilieo's is that mirrors can be made much larger than the lenses in Galileo's design, and so, much larger telescopes can be built.The largest refracting telescope in the world is the Yerkes telescope near Chicago USA. It has a lens 40 inches in diameter. Another of the largest is the Mount Palomar telescope in the USA uses Newton's reflecting design. It has a mirror which measures 5 metres or 200 inches in diameter!The Keck telescope in Hawaii uses an array of 36 mirrors that combine to measure 10 metres across.You must NEVER look at the Sun through a telescope, doing this would cause irreparable damage to your eyes.Telescopes make a distant object look larger but they also magnify the light making faint objects seem much brighter.Through a telescope the famous Orion nebular can be seen in great detail. And the Andromeda galaxy is a sight to behold.In 1991 NASA launched the Hubble space telescope into orbit around the Earth. It is a reflecting telescope with a primary mirror of 2.4metres ( or 94inches) in diameter. Because it is above the Earth's atmosphere it has given us unprecedented images of deep space objects.But visible light is only a small part of the spectrum. Objects can also emit radio waves and for these we have Radio Telescopes.Radio telescopes have a giant dish which catches and reflects the radio signal to a receiver placed at the focal point.One of the largest radio telescopes is situated at Jodrell Bank in Northern England. It was established in 1945 by Sir Bernard Lovell.So whether you're all at sea or high in the sky, there is always something to see with a telescope.
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