Suppose an object is at rest and that it is emitting radiation. An observer at rest with respect to the object observes the radiation to be blueshifted from its original frequency. This blueshift can be caused by
Consider four different regimes of space in which distances between objects might be changing as a result of the general expansion of the universe: (1) distances between different parts of Earth; (2) distance between planets in the solar system; (3) distances between stars in the Milky Way; (4) distances between clusters of galaxies. In which of these regimes are the distances changing because of the universe's expansion?