![]() ![]() If a lens is concave or diverging, it takes parallel rays and bends them so that they spread out. The distance from the lens to the focal point is called the focal length of the lens.ĭiagram of a convex lens, showing how the light is refracted and converges to a focal point. If a lens is convex or converging, it takes parallel light rays from a distant object and bends them so that they converge to a single point called the focal point. They are ground so that their surfaces are either segments of spheres or planes. Lenses form images by refraction and are typically made of either glass or plastic. In the diagram below, light is leaving air and entering glass, so it bends towards the normal on the way in, and away on the way out of the glass.ĭiagram showing how light changes direction as it moves into and out of a medium with a higher index of refraction. Light follows the same same principle and bends towards the normal when traveling into a medium with a higher index of refraction, and away from the normal when traveling into a medium where it can go faster. If the you approach the beach at an angle, one of the tires will be slowed down by the sand before the other is, and the car will turn in the direction of the tire that touched the sand first. If you approach the beach straight on, the car will slow down, but not change direction. Imagine driving a car from smooth pavement onto a sandy beach. The direction the light takes depends on whether it travels faster or slower in the new medium. If it enters at an angle, its speed and its direction will change. ![]() One time he was at it for sixteen hours straight.If light enters the new medium at a right angle to the surface, it will change speed, but not direction. There were times when I had to actually put food into William’s mouth because he could not stop grinding and polishing a mirror to eat. I know about this parabolic shape, as it is the design my brother used in making his own telescopes. A parabolic mirror is able to focus all of the light to one point and thus provides a crisper image than does a spherical mirror. It was fifty years before another member of the Royal Society, John Hadley, improved the mirror by making it have a parabolic shape instead of Newton’s spherical shape. The mirrors were hard to polish to the proper shape. ![]() Reflecting telescopes proved difficult to construct. One hundred years later, my own brother William would also be admitted to the Royal Society when he discovered Georgium sidus using a telescope based on Newton’s design. The demonstration was so successful that Newton was elected to membership to the Royal Society immediately. His telescope was shown to the Royal Society of London, one of the most distinguished organizations promoting science. Newton was not the only astronomer to think of building a telescope with a mirror, but he was the first to produce a working reflecting telescope. He experimented with different metals and polishing methods and made his first reflecting telescope in 1668. Instead of using a lens to focus the light from a star, Newton used a mirror. Newton started working on another type of telescope that he thought should get rid of chromatic aberration. Newton thought that it would be impossible to get rid of chromatic aberration as long as lenses were used in telescopes. The same thing happens with a lens but to a much lesser degree. When light passes through a prism the different colors separate and are discernible. He came to the conclusion that white light is really a mixture of light of different colors. In the mid 1600s, Isaac Newton was studying light and found that the bands of color plaguing early astronomers were formed from light passing through a lens or a prism. Without the high quality he achieved with his telescopes, a quality that far surpassed anything that had been accomplished before, he would not have been able to discover Uranus.Ĭredit: Adler Planetarium & Astronomy Museum ![]() He first thought the object was a comet, but later discovered it was in fact a new planet that he would name Georgium sidus after King George III astronomers would rename the planet Uranus, 50 years later. Herschel Reflecting Telescope: One night, using a reflecting telescope of his own design, William Herschel discovered an object moving across the sky. ![]()
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