One of the standard myths of science is that the world had to wait until Bessel first measured stellar parallax in 1838 before we had empirical proof of heliocentricity. Apart from the fact that Bessel was not the first to record stellar parallax, he was the first to publish, (but that’s another story) this is not true because James Bradley, who died 247 years ago today, delivered empirical proof of heliocentricity 110 years earlier with his observations of stellar aberration.
All of you know those wonderful time elapse photos of the city at night where the light from car headlights is drawn out into iridescent snakes or the ones of a golf club fitted with a small light source on its head illustrating in curves of light the golfers swing, this is light aberration. The movement seems to draw out the point light source into an incandescent worm. Now it doesn’t matter if it’s the light source or the observer that moves, the effect is the same. In the 1720s Bradley was trying to observe stellar parallax when he noticed that the position of the stars that he was observing described a small ellipse over the period of a year. What he was observing, which his calculation confirmed, was the annual orbit of the earth around the sun transformed into light aberration of the stars that he had been observing. This discovery published in 1728 in the Philosophical Transactions of the Royal Society was, as already stated, the first empirical proof of heliocentricity.