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Roemer delay

(timing differences in observed phenomenon due to Earth's position)

A Roemer delay is a delay in the appearance of a transient as observed from Earth, due to a greater distance between Earth and the phenomenon, in turn, due to the Earth's position in its orbit.

An example: when you check the observed times of the evenly-distributed pulses emitted by a pulsars, there is an observed delay (the Roemer delay) due to the Earth being at point of its orbit furthest from the pulser as compared to the times when the Earth is at the point nearer the pulsar. The EMR took longer to reach Earth. This delay-phenomena was first described centuries ago regarding observations of the orbits of Jupiter's moons over the course of years.

Further reading:

Referenced by pages:
pulsar timing array (PTA)
terrestrial time (TT)