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AST 309L
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Review for Last Test

AST. 309L - REVIEW FOR LAST TEST
  1. Communication
    1. Basics
      1. EM radiation much cheaper than travel
      2. Longer wavelengths = lower energy
      3. Beamsize on sky; prop. to w.l., inv. prop. to tel. size; diffraction
      4. Intensity decreases as square of distance
      5. Larger tel. more sensitive, but smaller area of search
      6. Largest existing telescope, Arecibo, 300 m
    2. Radio photons are best, especially 1 - 10 GHz (1000 - 10,000 MHz)
      1. Lower energy, less galactic absorption/interference,
      2. "Quantum noise" at short w.l.; galactic interference at long w.l.
      3. "Floor" set by cosmic background from big bang
    3. "Magic" wavelengths?
      1. H I - 1420 MHz (21 cm), most common
      2. Water hole, 1420 - 1720 MHz (1.4 - 1.7 GHz)
      3. Kuiper-Morris freq. from fundamental constants, 2.5 GHz
    4. Ways to encode information - vary wave: amplitude, freq., polarization
    5. Transmissions from earth
      1. Leakage radiation - strongest is defense radars
      2. "Light sphere" not very large yet; radius ~ 100 l.y.
      3. Sagan-Drake message to M13; image with dimensions= prime numbers
    6. Listening
      1. Cosmic haystack - # positions in sky, sensitivity, frequency range
      2. Most searches a compromise in one or more dimensions
      3. Larger bandwidth -> more noise; smaller -> possible Doppler shift out of band
      4. Search strategy depends on guesstimate of N; if large, can do small area/deep survey; if small, must survey whole sky
    7. Specific searches - previous
      1. Drake/Ozma; Zuckerman-Palmer/Oz II; Dixon-Cole/10^6 Oz; Horowitz/Meta (half dozen possibles) 10^9 Oz, most at H I freq.
      2. NASA SETI. 10^4 Meta, All-sky survey + targeted search
    8. Recent searches completed or ongoing
      1. BETA - started 1995 - covers water hole, northern sky
      2. Project Phoenix - observed Southern sky in Australia; two receivers few x 100 miles apart to eliminate terrestr. interference; northern sky in WVa (about 1000 nearby sun-like stars), 1-3 GHz
      3. Serendip - piggyback receivers on radio astronomy experiments
    9. Soon - Allen Telescope Array - 350 x 6-meter antennas, 1 - 10 GHz
  2. Travel
    1. Round trips are essentially impossible - even with antimatter fuel mass ratio = 14^4 for 0.99c
    2. Technology - current to dreamlike
      1. Pioneer 10 - .00003c= 10km/s (130,000yrs to nearest star)
      2. Project Orion - A bombs - 130 yrs
      3. Project Daedelus - fusion - 50 yrs
      4. Bussard's ramjet, solar and laser sails, antimatter fuel
      5. Main problem - containment of high temp. of burning fuel
    3. Relativity
      1. Increase in mass of rocket, slowdown of time for travellers
      2. Increase in mass of particles hitting rocket!
    4. Message Probes
      1. Cheaper than manned flight, short conversation time
      2. Bracewell probe - wait in orbit until hears life
    5. Colonization
      1. Reasonable arguments suggest whole galaxy should be!
      2. So where are they - why aren't they here? (Hart Hypothesis)
    6. UFO's
      1. Most reports easily repudiated; Venus, birds, insects, ...
      2. Why do we never have real evidence?
      3. Human brain wants to believe in them
      4. Engine power easily detectable with astron. telescopes
      5. Some phenomena may be interesting natural phenomena, (e.g. fireballs from seismic activity)







 





30 November 2006
Astronomy Program · The University of Texas at Austin · Austin, Texas 78712
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