Since 1967 the standard definition for the second has been based on which of the following?
a. characteristic frequency of the cesium-133 atom
b. average solar day
c. sidereal day
d. Greenwich Civil Time
e. None of the above
a
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The fact that most moons always show the same face to their planet is
A) very surprising and a great mystery. B) a natural consequence of the fact that the entire solar nebula rotated in the same direction. C) explained by the law of conservation of angular momentum. D) a natural consequence of tidal forces acting on the moons. E) a result of the fact that the moons once had atmospheres.
The percentage (by mass) of the Sun that is Hydrogen is about:
A) 91%. B) 71%. C) 27%. D) 9%. E) less than 1%.
One of the first tests of the general theory of relativity was the ____
a. description of the orbit of the moon b. determination of the speed of light as a constant c. change in mass of a particle moving at a high speed d. demonstration of a hammer and a feather falling at the same rate on the moon e. determination of the rate of advance of the perihelion of Mercury's orbit
The interior layer just below the crust of Earth is called the ________.
A. inner core B. mantle C. troposphere D. outer core