Aberration of starlight and the one-way speed of light

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“Simple stellar aberration diagram” by BlankAxolotl – inkscape. Licensed under CC BY-SA 3.0 via Wikipedia

The aberration of starlight (also called stellar aberration) is an astronomical phenomenon which produces an apparent motion of stars about their locations dependent on the velocity of the observer. Aberration causes objects to appear to be angled or tilted towards the direction of motion of the observer compared to when the observer is stationary. The change in angle is very small, and specified by the ratio of v/c where c is the canonical speed of light and v the velocity of the observer. With annual stellar aberration, the apparent change in the position of a star varies as observed by an Earth observer periodically over a year as the Earth’s velocity changes as it revolves around the Sun, with a maximum angle of about 20 arc-seconds in right ascension or declination. It traces a small ellipse on the sky over that time.

The fact of stellar aberration, which has been explained by a constant speed of light c, has been used by some to “refute” the idea of an infinite one-way speed of light in Lisle’s ASC model. The claim is that aberration would not occur at all if the one-way incoming speed of light was infinite, thus v/c = 0, here.  Dr Jason Lisle responds to this claim.


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