User:Ahalda/aberration
From Wikipedia, the free encyclopedia
The aberration of light (also referred to as astronomical aberration or stellar aberration) is a relativistic phenomenon which causes objects to appear displaced to observers in motion. It is notable in astronomy for causing an apparent motion of stars and other celestial objects about their locations in the sky. It was historically influential in the development of the theories of heliocentrism, light, luminiferous aether, and Special Relativity.
Aberration causes objects to appear displaced towards the direction of the observer's motion by an angle of approximately v/c (in radians), where c is the speed of light and v is the observer's velocity. It occurs for much the same reason that falling rain appears to come from ahead to observers in a moving vehicle. Aberration's main astronomical consequence is "annual" aberration, which causes stars viewed from the Earth to appear to move in the sky over the course of a year in small ellipses with an angular radius of approximately 20 arcseconds, due to the finite speed of light relative to motion of the Earth as it revolves around the Sun.
Aberration was first observed around 1680 by a number of astronomers including Robert Hooke and John Flamsteed, who were instead searching for stellar parallax, but it was misunderstood for many years. James Bradley was the first scientist to understand it classically in 1729, and his theory and astronomical observations of aberration provided the first empirical proof of heliocentrism, convinced the scientific world that the speed of light is finite, and allowed him to make one of the earliest measurements of the speed of light.
In the 19th century aberration paved the way to the theory of Special Relativity. Thomas Young theorized that aberration implied the existence of an "aether wind" in 1804, and François Arago attempted to measure variations in the speed of light using aberration in 1810, but did not detect any. These observations were the main motivation for the aether drag theories of Augustin Fresnel (in 1818) and G. G. Stokes (in 1845), which, in combination with with new experiments and theory, led to Hendrick Lorentz' electromagnetic aether theory in 1892. Based on Lorentz' theory and on other observations, Albert Einstein then developed the theory of Special Relativity in 1905, and said that aberration was one of the experimental results which most influenced him.