T = T source = 1 second for example

Blueshift

Redshift

shift z

−0.5

−0.1

1

10

Distance of B source from A:

β source (SR)

−0.60

−0.10

0.60

0.98

d: distance of emission of B from O

c T

c T

−0.6 c T

−0.98 c T

Length traveled by photon B:

T observed/T source = (1 + z)

0.5

0.9

2

11

L: Length traveled by photon B

0.5 c T

0.9 c T

c T

10 c T

Difference δ

−0.5 c T

−0.1 c T

0.4 c T

9.02 c T