Empirical Earth · The Sky — Sun, Moon & Stars
Parallax & aberration — catching the Earth in motion around the Sun
The claim
“The Earth is motionless; if it orbited the Sun the stars would shift — and they don’t.”
What is measured
Nearby stars shift by under an arcsecond each year (61 Cygni: 0.314″, Bessel 1838) as Earth orbits. That is direct proof the Earth moves.
What would show this is wrong
a nearby star showing no annual parallax ellipse against the far background.
Sources
- Stellar parallax. Friedrich Bessel measured the parallax of 61 Cygni at 0.314 arcseconds in 1838 (the first stellar parallax), implying ~11 ly. Parallax (the yearly shift of nearby stars aga link
- Aberration of light. James Bradley discovered stellar aberration in 1727 — a ~20.5″ annual shift of every star caused by Earth's ~30 km/s orbital velocity combined with the finite speed of l link
- Gaia, the parsec and modern parallax. ESA’s Hipparcos (1989) measured over 100,000 stellar parallaxes and Gaia more than a billion to ~10-microarcsecond precision; Proxima Centauri’s paralla link
- Measuring the transit of Venus parallax (2012). From simultaneous images taken in New Jersey and Hawaii (7,835 km apart) during the 5 June 2012 transit, R. J. Vanderbei measured Venus’s para link
- The transit of Venus and the astronomical unit. Diurnal parallax during a Venus transit, observed from widely separated points on Earth, was the classical method for measuring the Earth–Sun link
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