Consider a telescope, pointing in a direction perpendicular to the momentary direction of the earth's movement in its orbit: in the time the light of a star needs to arrive from the objective to the eyepiece, the earth has already advanced on its course. I must therefore tip the telescope through an angle \( \alpha\), in order for the star to be presented in the center of the visual field.
This angle defines the light deviation due to the movement of the earth.
The formula to apply in the case of this aberration is:
\( \tan \alpha = v/c \) where \( v \) is the velocity of the earth in its orbit, \( v \simeq 30 Km/s \).
The angle has a size of approximately 20 arcsecond.
Epstein Explains Einstein
An Introduction to both the Special and the General Theory of Relativity
“As simple as possible - but not simpler !”
by David Eckstein
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