Question

What major orbital problem of the late 1800s is solved by general relativity?

Answer 1

General relativity solves the problem of Mercury's perihelion motion in the late 1800s, which couldn't be explained by Newton's law of gravitation. The curvature of space-time caused by the Sun's gravity is responsible for the observed advancement of Mercury's perihelion beyond what Newtonian gravity predicts.

The major orbital problem of the late 1800s that is solved by general relativity is the anomalous motion of Mercury's perihelion. According to Newton's law of gravitation, the perihelion position of Mercury's elliptical orbit should remain fixed over time. However, careful measurements showed that it was slowly advancing, and this discrepancy couldn't be explained by the gravitational pull of other planets alone. General relativity predicts, and subsequent observations confirmed, that the curvature of space-time caused by the Sun's gravity causes the perihelion to advance slightly more than predicted by Newtonian gravity.

Answer 2

That would be the precession of Mercury's perihelion.

In simpler terms this would mean that the Mercury's orbit, perihelion, did not behave as it should according to the Newton's laws. That is its rotation of the orbit, the precession, was strange as it was at its closest to the sun at different places as it slowly moves around the sun.