What is a Cepheid variable?
A) It is a bright source of variable X-ray emission, thought to harbor a supermassive black hole.
B) It is a type of very luminous star that makes an excellent standard candle.
C) It is a main-sequence star of spectral type B5.
D) It is a type of galaxy that varies in its light output.
B
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The science of changing the activation enthalpy of a process is called _____________.
Fill in the blank(s) with the appropriate word(s).
That Earth ____ , evidence that Earth differentiated
a. rotates slowly b. has an average density that is higher than the density of the crust c. has a no magnetic field d. has a surface that is 75% water e. all of these
The youngest parts of Earth's crust are
a. the bottom layer found in the walls of the Grand Canyon. b. the continents. c. the continental margins. d. the Appalachian Mountains. e. the mid-ocean rifts.
In which direction does a quarter Moon rise?
A) north B) south C) east D) west E) The Moon becomes a quarter Moon only after it has risen and changed phase.