How did Bradley determine the speed of light in 1779 from stellar parallax?
Based on information from Isaac Asimov’s Biographical Encyclopedia of Science and Technology: “In 1727, while looking for evidence of parallax, James Bradley discovered stellar aberration, another annual effect, but much larger. For a star in a direction normal to the Earth’s orbit around the Sun, this aberration angle in radians, as seen from the Sun, is essentially (orbital velocity/speed of light) = v/c, and turned out equal to 10(-4). Using a value for Earth’s orbital velocity close to 30 km/sec, Bradley arrived at a value for the speed of light close to the modern value of 300,000 km/sec and better than the 227, 000 km/sec that had been announced by Olaus Roemer in 1676.
