Stars at different distances from the galactic center revolve with different periods, an effect ...

Stars at different distances from the galactic center revolve with different periods, an effect called _______________ rotation.
 
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Question 2

The term _______________ refers to a change in velocity.
 
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Question 3

The galactic _______________ contains very little gas and dust, old stars, and globular clusters.
 
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Question 4

The _______________ states that an observer cannot distinguish locally the difference between inertial forces due to acceleration and uniform gravitational forces due to the presence of a massive object.
 
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Question 5

An astronomer named _______________ used globular clusters to locate the center of the galaxy. (enter last name only)
 
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