The precession of Mercury refers to the observed anomaly in the orbit of the planet Mercury around the Sun. This phenomenon has played a pivotal role in the history of physics, particularly in the development and acceptance of general relativity.
In the 19th century, astronomers noted that Mercury's orbit did not perfectly follow the predictions made by Newtonian gravity. Urbain Le Verrier, in 1859, calculated that Mercury's perihelion (the point in its orbit closest to the Sun) was advancing by about 574 arcseconds per century more than predicted by Newtonian mechanics. This discrepancy was initially thought to be due to the gravitational influence of an undiscovered planet, which was dubbed "Vulcan".
Newtonian mechanics predicted that the gravitational pull of other planets would cause Mercury's orbit to precess, but this effect was insufficient to account for the full observed precession. The additional precession was:
In 1915, Albert Einstein introduced his theory of general relativity, which fundamentally changed the understanding of gravity. According to general relativity, the curvature of spacetime around a massive object like the Sun affects the orbits of planets. Einstein calculated that the additional precession of Mercury's orbit due to the curvature of spacetime near the Sun would be exactly 43 arcseconds per century, perfectly matching the observed anomaly:
"The explanation of the precession of Mercury was one of the first and most striking confirmations of the theory of general relativity." - Einstein's Nobel Lecture
The explanation of Mercury's precession by general relativity:
Modern observations continue to support Einstein's prediction with ever-increasing precision: