In the equation: Number of Civilizations = Np × flife × fcivilization × fnow what do we mean by fnow?
A) the fraction of planets with civilizations on which the civilizations exist now
B) the fraction of time since the Big Bang represented by the present era
C) the fraction of all species ever to exist that we currently are aware of
D) the fraction of planets in the galaxy on which a civilization could theoretically develop now
E) the fraction of civilizations in the universe that currently are sending messages to us
A
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The rings of Uranus were discovered during a(n) _______________ when Uranus crossed in front of a star
Fill in the blank(s) with correct word
Elementary Particles: The proton is made up of which one of the following quark combinations (up, down, strange, charm, top, bottom)?
A. uud B. ddu C. udd D. ttb E. bst
The largest nearby cluster of galaxies lies about 17 Mpc distant in
A) Sagittarius. B) Sculptor. C) Coma Bernices. D) Virgo. E) Ursa Major.
A concave mirror has a focal length of 20 cm. What is the magnification if the object's distance is 100 cm?
a. 1/2 b. 1/4 c. ?2 d. 4 e. ?1/4