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by: Stephan Kuvalis


Stephan Kuvalis

GPA 3.89

Philip Armitage

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About this Document

Philip Armitage
Class Notes
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This 3 page Class Notes was uploaded by Stephan Kuvalis on Thursday October 29, 2015. The Class Notes belongs to ASTR 3300 at University of Colorado at Boulder taught by Philip Armitage in Fall. Since its upload, it has received 21 views. For similar materials see /class/231955/astr-3300-university-of-colorado-at-boulder in Astronomy at University of Colorado at Boulder.




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Date Created: 10/29/15
SETI With current technology difficult to detect unintentional leakage from other civilizations at usetul distances An advanced civilization could choose to construct beacons that would be detectable today Search needs to target many stars at high sensitivity with narrow trequency channels Depending upon the nature of the signal being sought can be advantageous to trade off these factors e g one super powertul beacon in the Galaxy would best be found with a low sensitivity all sky survey Exbatelrestrial Life Spling2008 SETI at home Distributed computing project to analyze passively acquired data from Arecibo primarily in a 2 5 MHz band centered on 1420 MHz Due to Doppler shift frequency of a narrowband artiticial signal will dritt due to the changing motion between the Earth and another planet rate of 0 1 Hz s Computational task is to search across many trequency channels and all possible dritt rates About 3 million PCs participating in the effort ATA search strategy Search 100 000 stars for artificial signals Sensitivity good enough to detect the equivalent of the Arecibo planetary radar out to 1000 light years in the frequency band 1 10 GHz Survey 4 x 101 stars in the Galactic plane toward the center of the Galaxy for super powertul beacon transmissions Telescope will also be the best instrument for some non SET radio astronomy searches for radio counterparts to gamma ray bursts timing of pulsars 39 Life Spring 2008 SETI searches Proiect Phoenix Search between 1995 2004 on large radio telescopes 700 nearby stars surveyed 1 2 3 GHz in 0 7 Hz trequency channels 2 10 minutes observing time per star sensitivity 103926 W m2 Used a pair of widely separated dishes to allow for a determination that sources were actually coming from the sky and were not radio frequency interterence 1 000 000 candidate signals 1 000 that appeared to be from the sky none that survived further examination Exbatenestrial Life Spring 2008 W New array of radio telescopes under construction in California First 42 dishes were activated last October goal is 350 dishes each of 6 1m diameter Frequency coverage 1 10GHz 10 billion 1 Hz channels Each antenna is small so wide field of view within this field multiple targets can be identified in software post processing of the data Ex aterrestyial Life SplingZOOB Square kilometer array Proposed next generation radio telescope to be sited either in Western Australia or South Africa 1 square km of collecting area similar all digital design to Allen telescope For SET could survey 1 000000 stars for signals of comparable strength to current terrestrial emission Extraterrestrial Life Spring2008 Null results and the Drake equation Nciv N XfHP X fzie X civ X alive Suppose we search 1 000 000 stars and find no evidence for artificial signals t we assume that any presently alive civilization would send signals then estimate 5 Could write this as a limit on the prOduct flifefcivfalive Clearly current and planned searches do not place very strict limits on the number of intelligent civilizations in the Galaxy especially since its not clear other civilizations would send signals Extraterrestrial Life Spring 2008 Fundamental limitations All evidence suggest that the speed of light c is the absolute upper limit for the propagation of any material object signal or information transfer Einstein s special theory of relativity As seen from Earth cannot make it to the nearest stars d N 3 light years in less than 3 years unless there are fundamental errors in our understanding of physics However as seen from an astronaut on board a craft time is slowed bya tactor Relativistic phenomenon called time dilation 39 I 39r Spring2008 Energy requirements For non relativistic speeds v ltlt c the kinetic energy of a spacecraft of mass m traveling at speed v is e g to accelerate a probe of mass 100 kg to 10 ot the speed of light energy requirement is EKE 0 5 x100 kg x3x107 nvs2 4 5x1016 Joules Not a crazy number about the energy output of a 1 GW power station for one year 39 Life Spring 2008 nterstellar travel Could we send a probe to nearby stars Example Voyager 1 probe has a current velocity of 17 000 km per hour 4 700 ms1 Distance to the nearest star is about 3 light years 3x95x10 5m3x10 6m 3x1016 In Travel time t 7 4700 ms 6 gtlt1012 s 200000 years Need to do much better it interstellar travel is ever to be practical Extraterrestrial Life Spring 2008 Time dilation only becomes significant at velocities close to the speed of light eg V01c y1005 1 year of Earth time 0 995 years on spacecratt V 0 99 C y 7 1 year of Earth time 1 7 months on spacecratt t we could accelerate spacecraft to very close to the speed of light would be possible to make trips to the nearby stars within human litetimes Extraterrestrial Life Spring2008 Problem is that the fuel required to yield that much energy is very heavy e g liquid hydrogen has an energy density of about 140 MJ per kg 14 x108Jouleskg To supply the energy requirements of our hypothetical 100 kg probe would need 300 000 tonnes of fuel 39 Life Spring 2008 Ways around this Qroblem discard the fuel tanks as you go the principle of staging used or all current rockets use more efficient fuel higher energy density don t carry the fuel with you accept extremely long journey times energy goes as the squ 39 are of the velocI y and even a million years is very short compared to lifetime of Galaxy


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