Briefly describe how astronomers estimate the number of galaxies in the observable universe.
Fill in the blank(s) with the appropriate word(s).
Answer: Astronomers can count galaxies in small regions of the sky that have been photographed in great detail by powerful telescopes (e.g., with photos like the Hubble eXtreme Deep Field). They can then estimate the total number of galaxies in the observable universe by multiplying the number of galaxies in the small region of the sky by the number of such regions it would take to cover the entire sky.
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According to the parameters derived for the Drake Equation, where should astronomers look for life in the Milky Way?
A) around F, G, or M stars that are in multiple star systems located in the galactic habitable zone with a multiple planet system with jovian outer planets and at least one terrestrial planet within the star's habitable zone B) around O, B, or A stars that are in single star systems located in the galactic nucleus with a multiple planet system with jovian outer planets and at least one terrestrial planet within the star's habitable zone C) around F, G, or M stars that are in single star systems located in the galactic habitable zone with a multiple planet system with jovian outer planets and at least one terrestrial planet within the star's habitable zone D) around O, B, or A stars that are in single star systems located in the galactic habitable zone with a multiple planet system with jovian outer planets and at least one terrestrial planet within the star's habitable zone E) around F, G, or M stars that are in single star systems located in the galactic habitable zone with a multiple planet system with no outer planets and at least one terrestrial planet within the star's habitable zone
The torque due to the frictional resistance of the oil film between a rotating shaft and its bearing is found to be dependent on the force F normal to the shaft, the speed of rotation N of the shaft, the dynamic viscosity ? of the oil, and the shaft diameter D. Establish a correlation among the variables by using dimensional analysis.
GIVEN The oil film between a rotating shaft and its bearing The torque (T) due to frictional resistance is a function of normal force (F), speed of rotation (N), dynamic viscosity (?), and shaft diameter (D) FIND A correlation among the variables ASSUMPTIONS Steady state
What was the key physical property in determining the two categories of planets during solar system formation?
a. pressure b. gravity c. density d. momentum e. temperature
A sound level of 80 dB has ___________ the amplitude of a 60 dB sound
a. ten times b. twenty times c. one tenth d. twice