 
Summary: Extraterrestrial Life: Homework #6
Due, in class, Thursday April 24th
1) Make your own estimates for the values of each of the terms in the Drake
equation discussed in Lecture #19. There are no "correct" values, so
explain how you arrived at each estimate. Use your numbers to calculate
the estimated number of civilizations presently alive in the Galaxy.
2) Suppose that a SETI search is sensitive enough to detect a 1MW signal
broadcast from a civilization at a distance of 1000 light years. Suppose we
wish to use the same search to look for civilizations 50,000 light years
away on the far side of the Galaxy. How powerful would the alien
transmitter have to be for us to have a chance of success?
3) Explain briefly what is meant by the bandwidth of a signal.
4) The "Galactic Communication" applet at:
http://cosmos.colorado.edu/stem/applets/
provides a visual depiction of some of the challenges of interstellar
communication. Using the applet, you can set the birth rate of civilizations
in the Galaxy (in units of civilizations born per 100,000 years), as well as
the average lifetime of civilizations (note that this is a random quantity, so
if you set the mean to be say 1000 years sometimes Earth's civilization will
last for 500 years and sometimes for many thousands of years). By clicking
