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Telescopes
• Act as “electromagnetic radiation catchers”• Capture as much as possible
• Focus
• Magnifies images
Telescopes that “catch” visible light are called optical telescopes.
Telescope Terms
• magnification (power) – how strong the telescope is.
• resolution - how close two objects can be and yet still be detected as separate objects.
• aperture – diameter of the lens or mirror
Reflector Telescopes
• Isaac Newton developed the reflector about 1680.
• Newton used a curved, metal mirror to collect the light and reflect it to a focus.
• Because the mirror reflected light back into the tube, he had to use a small, flat mirror in the focal path of the first mirror to deflect the image out through the side of the tube, to the eyepiece; otherwise, his head would get in the way of incoming light.
Refractor Telescopes• Galileo (1609) is the first to use it for astronomy.
• The objective lens gathers the light, and bends or refracts it to a focus near the back of the tube. The eyepiece lens brings the image to your eye, and magnifies the image.
• Refractors have good resolution, high enough to see details in planets and stars.
• It is difficult to make large objective lenses (greater than 4 inches or 10 centimeters) for refractors.
• Refractors are relatively expensive
Compound Telescopes• The first compound telescope was made by
German astronomer Bernhard Schmidt in 1930
• The compound telescope is the best, all-around telescope, good for viewing lunar and planetary observations. It is portable and compact and is the most versatile
• Uses a combination of mirrors to fold light rays and form an image.
• Has an equatorial mount that allows it to spin in every direction.
Multiple Mirror Telescopes (MMT)
• Works like a reflecting telescope, but uses many mirrors to create 1 large mirror.
• Can create bigger mirrors
• Mirrors weigh less and distort less
Hubble Telescope
• Hubble orbits 600 kilometers (375 miles) above Earth, working around the clock to unlock the secrets of the Universe. It uses excellent pointing precision, powerful optics, and state-of-the-art instruments to provide stunning views of the Universe that cannot be made using ground-based telescopes or other satellites.
The Very Large Telescope (VLT)
• Cerro Paranal, Chile
• Uses 4 separate large telescopes as well as several other small telescopes to create 1 large telescope.
• The large telescope mirrors are 8 meters across.
Radio Telescopes
• Karl Jansky inadvertently discovered galactic emissions of radio waves in 1933
• Like optical telescopes, radio telescopes have reflectors and receivers
• Most radio telescopes need to be large in order to accommodate radio's longer wavelengths and lower energies
• Can “see” day or night
Arecibo (Puerto Rico)
The main reflector is 1000 feet in diameter
It can see 1/3 of the skyat a time