General relativity explains a small, unexplained part of Mercury’s perihelion advance: about 43 arcseconds per century. The much larger share of the orbit’s precession comes from gravitational perturbations by other planets. The Sun’s mass curves spacetime, adding the residual advance that Newtonian calculations alone do not account for.
What is Mercury’s perihelion, and what does it mean for it to advance?
Perihelion is the point in an orbit closest to the Sun. Mercury follows an ellipse, and its perihelion advances when the ellipse’s orientation gradually changes. The advance describes a rotation of the orbit’s direction over time; it does not mean Mercury simply moves closer to the Sun on every pass.
![Relativity: The Special And The General Theory by Albert Einstein [Deluxe Hardbound Classic] - Theories of Relativity / Space And Time Timeless Theories](https://m.media-amazon.com/images/I/51MFuTNvyPL._SL160_.jpg)
As an Amazon Associate I earn from qualifying purchases.
The total advance has more than one cause. The planets’ gravitational pulls perturb Mercury’s orbit, while general relativity contributes an additional shift. Keeping those contributions separate is essential: the relativistic figure is the residual, not the whole observed precession.
How much comes from planets, and how much from relativity?
Planetary perturbations explain most of Mercury’s perihelion precession. General relativity accounts for the smaller remaining amount, historically measured as a mismatch after the Newtonian planetary effects were included.
#1 Best Overall
| Contribution | Approximate advance | What it describes |
|---|---|---|
| Other planets’ gravitational perturbations | About 531 arcseconds per century in OpenStax’s account; a NASA MESSENGER analysis reports approximately 531.63 arcseconds per Julian century. | The dominant Newtonian contribution from other bodies perturbing Mercury’s orbit. |
| General relativity | About 43 arcseconds per century in NASA and OpenStax educational sources; the MESSENGER analysis reports approximately 42.98 arcseconds per Julian century. | The additional relativistic contribution associated with the Sun’s curved spacetime. |
These figures are rounded or reported using a Julian century, depending on the source; they should not be treated as interchangeable to arbitrary precision. OpenStax presents the approximate contributions in Astronomy 2e. The more specific values appear in NASA’s Planetary Geodesy Data Archive and the 2018 MESSENGER analysis in Nature Communications.
Why does general relativity change Mercury’s orbit?
In general relativity, the Sun’s mass changes the geometry of spacetime around it. Mercury travels through that curved spacetime, and its orbit gains a small additional advance beyond the one predicted from Newtonian planetary perturbations alone. NASA describes the Sun’s spacetime warping as the second-largest contribution to Mercury’s motion, after the effects of the other planets.
This is a general-relativistic effect, not an explanation based on special relativity. Stanford’s Gravity Probe B FAQ distinguishes the two theories in this context. NASA’s explanation of tracking Mercury also discusses the Sun-related contribution and the historical problem.
Free tools Windows power users keep installed
One-click scans. No signup required.
Was Mercury’s anomaly discovered after Einstein proposed relativity?
No. Astronomers had identified an unexplained advance in Mercury’s perihelion before the mature theory of general relativity. The discrepancy became a notable early test of Einstein’s theory: relativity provided an explanation for the residual without requiring an additional planet. Einstein did not first observe the motion; the theory explained a known problem in celestial mechanics.
The National Academies’ chapter on relativity and Mercury’s perihelion discusses that history. NASA’s educational fact card likewise describes general relativity as explaining the observed precession without an extra planet: NASA Space Place: Mercury’s perihelion.
Quick Recap
Best Value
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
