The great astronomer Edwin Hubble discovered that all distant galaxies are reced
ID: 1654311 • Letter: T
Question
The great astronomer Edwin Hubble discovered that all distant galaxies are receding from our Milky Way Galaxy with velocities proportional to their distances. It appears to an observer on the Earth that we are at the center of an expanding universe. Figure 3.64 illustrates this for five galaxies lying along a straight line, with the Milky Way Galaxy at the center. Using the data from the figure, calculate the velocities: (a) relative to galaxy 2 and (b) relative to galaxy 5. The results mean that observers on all galaxies will see themselves at the center of the expanding universe, and they would likely be aware of relative velocities, concluding that it is not possible to locate the center of expansion with the given information. Galaxy 1 300 Mly Galaxy 2 150 Mly Galaxy 3 MW Galaxy 4 190 Mly Galaxy 5 450 Mly v_1 = -4500 km/s v_2 = -2200 km/s v_4 = 2830 km/s v_5 = 6700 km/s Five galaxies on a straight line, showing their distances and velocities relative to the Milky Way (MW) Galaxy. The distances are in millions of light years (Mly), where a light year is the distance light travels in one year. The velocities are nearly proportional to the distances. The sizes of the galaxies are greatly exaggerated: an average galaxy is about 0.1 Mly across.Explanation / Answer
Concept is that, Velocity of A wrt B (Vab) = Va - Vb
where Va and Vb are velocityies of A and B wrt any common reference.
We are given Velocities of Galaxies wrt MW as V1, V2 , V4 and V5
Velocities of all Galaxies wrt galaxy2 are:
V( 52) = V5 - V2 = 6700 - (-2200) = 8900 Km/s
V(42) = V4 - V2 = 2830 - (-2200) = 5030 Km/s
V(32) = V3 - V2 = 0 - (-2200) = 2200 km/s
V(12) = V1 - V2 = -4500 - (-2200) = -2300 km/s
Velocities of galaxies wrt galaxy 5 are
V(15) = V1 - V5 = -4500 - 6700 = 11200 km/s
V(25) = V2 - V5 = -2200 - 6700 = -8900 km/s
V(35) = V3 - V5 = 0 - 6700 = -6700 km/s
V(45) = V4 - V5 = 2830 - 6700 = -3870 km/s
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