Telescope History • Galileo Galilei built first refractive telescope in 1609 • Isaac Newton built the first reflective telescope in 1668
Optical Telescopes • Telescopes that contain mirrors, lenses, or both • Three properties: • Light-gathering power • Resolving power • Magnifying power
Optical Telescopes • Telescopes with larger mirrors/lenses: • Can“see”farther into space • Have greater resolution • Magnification can be changed by using different eyepieces • Usually placed on mountain tops to reduce city lights
Refracting Telescopes • Telescope uses two lens to bend or refract light • Simplest of all telescopes • First refracting telescope capable of magnifying objects 30 times.
Objective Lens • Most important lens is the objective lens • Bends the light from a distant object and focuses the light at the focus to produce an image • The objective lens produces a very small, bright image of an object • Focus= central point • Focal length= distance between the focus and the objective lens
Eyepiece Lens • The second lens used in a refractive telescope • Eyepiece magnifies image produced by the objective lens
Disadvantages • Shorter wavelengths of light are bent more than the longer ones • Chromatic aberration: • Weakens image and creates a halo of color around it • When red light is in focus, a bluish halo appears. • Very hard to produce a large piece of high-quality, bubble-free glass
Reflecting Telescopes • Uses a concave (curved) mirror that focuses the light in front of it • Mirror is coated in a highly reflective material, an aluminum compound • Two mirrors- one large & concave and one small & flat
Advantages • No Chromatic aberration because reflected light is not dispersed into its component colors. • Glass does not need to be high-quality because light does not pass through it. • Disadvantage–secondary mirror blocks some light entering the telescope.
Invisible Light • Stars produce light wavelengths that are not visible to our eyes • Gamma rays, X-rays, ultraviolet radiation, infrared radiation, and radio waves • Most of these can not get past our atmosphere… so we must get our cameras above it!
Radio Telescopes • These big dishes are used to detect radio waves • Focuses incoming radio waves on an antenna and transmits these to an amplifier.
Radio Signals • Radio signals are weak so it requires a very large dish • These telescopes have poor resolution • Radio Interferometer= Wire several telescopes together
Advantages • Less affected by turbulence in the atmosphere, clouds, and weather • No protective dome is required = cheaper • Can be used and “viewed” 24 hours a day • Radio signals can pass through intersteller dust clouds
Disadvantages • Can be affected by human-made radio interference • Usually placed in valleys to block interference
Space Telescopes • Orbit above Earth’s atmosphere and produce clearer images
Hubble Space Telescope • Built by NASA and sent in April 1990 • 10 billion times more light-gathering power than the human eye • Given us amazing images of space
Other Space Telescopes • Chandra X-Ray Observatory • NASA uses to study X-rays • Launched in 1999 • Gather data about black holes • Compton Gamma-Ray Observatory • Used to study visible light and gamma rays • In 2018, NASA will launch James Webb Space Telescope to study infrared radiation • Run into many obstacles and budget problems