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Reflector Telescope1 - Alas Despite the advantages of the...

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Reflector Telescopes The reflector telescope uses a mirror to gather and focus light. All celestial objects (including those in our solar system) are so far away that all of the light rays coming from them reach the Earth as parallel rays. Because the light rays are parallel to each other, the reflector telescope's mirror has a parabolic shape. The parabolic-shaped mirror focusses the parallel lights rays to a single point. All modern research telescopes and large amateur ones are of the reflector type because of its advantages over the refractor telescope. Advantages 1. Reflector telescopes do not suffer from chromatic aberration because all wavelengths will reflect off the mirror in the same way. 2. Support for the objective mirror is all along the back side so they can be made very BIG! 3. Reflector telescopes are cheaper to make than refractors of the same size. 4. Because light is reflecting off the objective, rather than passing through it, only one side of the reflector telescope's objective needs to be perfect.
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Unformatted text preview: Alas! Despite the advantages of the reflector telescope, astronomers must contend with some minor annoyances. Disadvantages 1. It is easy to get the optics out of alignment. 2. A reflector telescope's tube is open to the outside and the optics need frequent cleaning. 3. Often a secondary mirror is used to redirect the light into a more convenient viewing spot. The secondary mirror and its supports can produce diffraction effects: bright objects have spikes (the ``christmas star effect''). Two famous reflector telescopes are shown below. The first picture is of the 5-meter (200-inch) Hale Telescope at Palomar Observatory. The number refers to the diameter of the objective (almost 17 feet across!). Clicking on the image will send you to a gallery of images of the telescope in another window. The telescope is the vertical piece in the middle with the mirror close to the floor. The huge diagonal piece is used to balance the telescope....
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