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Electomagnet (EM) Specrtrum
• All radiation, radio wave and light are part of the EM spectrum
• Visible light is only a very small section of the whole spectrum
Wavelength- Distance covered by one full cycle of a wave- commonly measured crest to crest
• CU physics site animation shows wavelengths
• http://www.colorado.edu/physics/2000/waves_particles/index.html
Arecibo
• The Arecibo radio telescope in Puerto Rico is the largest single dish telescope in the world.
• This 1000 foot dish was constructed over a natural crater. (= 0.3km = 0.2 mi)
VLA
• The very large array in Socorro New Mexico was built in the 1970’s.
• It uses 27 radio telescopes all linked together in a Y shape. These telescopes simulate a large radio telescope 40 km in diameter.
The SETI Project
• SETI stands for the Search for Extraterrestrial Intelligence.
• SETI began using the Arecibo telescope to look for alien signals.
• In 1974 the Arecibo telescope sent a megawatt signal to outer space.
Frequency- How often a complete wave passes a set point
• Long wavelength = low frequency
• Short wavelength = high frequency
#waves/time = cycles/sec = Hertz (Hz)
Energy in the wave
• Long wavelength = low frequency = low energy• Short wavelength = high frequency = high energy
Spectra are created from excited electrons in atoms
• Valence electrons absorb energy from heat, electricity, other EM emissions
• Electrons jump up to a higher energy level
• When electrons “fall” back to ground state they give off EM emisions
Kinds of spectrum
• Continuous spectrum- like the rainbow
• Absorbtion Spectrum - has rainbow with “black” lines in it
• Emmission spectrum – just a line or two or three…………. Of colored light
Doppler Effect
• Red Shift-move away– Lengthen wavelength– Color shifts toward red
end
• Blue shift-move toward– shorten wavelength– Color shifts toward
blue end
Mass of the universe determines fate
• More than critical mass collapse Big Crunch another Big Bang?
Does the universe occilate? Closed universe
Less than critical mass expands forever Open universe
HR diagram
• Graphs starsTemp (color or spectral class) vs Absolute
magnitude (Luminosity)
Absolute magnitude – brightness based on being the same distance away from each star
Apparent magnitude – brightness from Earth- all stars are different distances away
2 Famous Telescopes
• In the 1960” Robert Wilson & Arno Penzias won the Noble Prize for their discovery with the first large microwave telescope.
• COBE was a microwave / infra-red satellite in the 1980’s.
Visible “Optical” Telescopes
• Early history of optical telescopes.
• Modern day observatories.
• The future of optical telescopes.
Yerkes Observatory
• Built in 1897 the Yerkes telescope in Wisconsin is the largest refractor.
• It has 40 inch diameter lens!
The Mt. Wilson Hooker Telescope
• In 1908 the largest reflector telescope was built on Mt. Wilson overlooking Los Angeles.
• This Hooker telescope uses a 100 inch mirror to collect light.
The Palomar Observatory, Hale Telescope
• In 1948 the largest telescope was the 200 inch Hale telescope on Palomar Mountain, California.
The BTA Telescope
• Currently the largest single mirror telescope is the BTA, (Bolshoi Teleskop Azimutal) in Southern Russia.
• The BTA was built in 1975 and uses a single 230 inch mirror to collect light!
Multiple Mirror Telescopes
• After building the huge BTA telescope, astronomers realized that 200 inches is the maximum size for a telescope. Anything larger than 200 inches and the mirror becomes distorted under its own weight.
• The solution to this problem was to build multiple mirror telescopes.
Multiple Mirror Telescopes
• M.M.T. combine many mirrors to form one giant mirror. These mirrors are computer controlled to make a parabolic shape.
• The KECK telescope in Hawaii is currently the largest telescope in the world with a total of 400 inches of segmented mirrors!
3 Famous Observatories
• #1 Mauna Kea is Hawaii’s tallest peak and home to the largest telescopes in the world.
• #2 Las Campanas Chile has some of the clearest seeing on the the planet.
• #3 Kitt Peak Observatory in Tucson Arizona has a large collection of telescopes.
Current Problems
• Aside from money, two of the biggest problems facing optical observatories are:
• 1. Light Pollution
• 2. Atmospheric turbulence
The Hubble Space Telescope
• By placing a telescope in orbit you solve the problems of light pollution and atmospheric turbulence.
• In 1990 the space shuttle Discovery was launched with the 90 inch Hubble Space Telescope.
The Future of Optical Telescopes
• The NGT (Next Generation Telescope) will be a 300 inch multiple mirror orbiting space telescope.
• The ELT will be a 30 meter (3 times larger than the Keck) segmented mirror telescope.
Ultra-Violet Telescopes
• UV telescopes must observe from outer space.
• These telescopes specialize in observing the sun.
• The IUE is the International Ultra-Violet Explorer space telescope.
X-Ray Telescopes
• X-Ray telescopes study high energy objects like black holes.
• The Chandra X-Ray telescope was launched into space two years ago.
Gamma Ray Telescopes
• Gamma Ray telescopes study very high energy objects like gamma ray bursters and supernova explosions.
• The Compton Gamma ray telescope was the most famous of these telescopes.