 Solution

ID: past-exam-of-the-physics-course-of-the-year-4-of-the-natural-sciences-course-of-the-university-of-cambridge/2014/paper-1/b4/b/solution

x (t)

t

was emitted at

t_{e} = t - x (t) / c

. Differentiating gives

d t_{e} / d t = 1 - β

. Since

R d t_{e}

photons arrive in

d t

R_{hit} = R (1 - β) .

The emission rate and impact rate refer to different events, even though both are expressed in Earth coordinate time.

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