# First observation that the movement of a planet or asteroid in its orbit was affected by another planet?

Answers to the question How did Kepler determine the orbital period of Mars? describing careful observations centuries ago got me thinking.

Question: What was the first analysis of observations that directly demonstrated that the movement of a planet or asteroid in its orbit was affected by gravitational attraction by another planet?

I don't mean inferences based on the spacing of orbits, I'm thinking of detailed positional measurements; something like planet/asteroid A was X kilometers or Y arcseconds away from it's predicted position and it couldn't be accounted for if not for the gravitational effects of planet B.

I am not sure if First observation that the Sun and Jupiter (and friends) move around a common barycenter? is a completely separate question, or if this confirmation happened all at once, but I've currently asked it separately.

• To what I know I think there were two of these, but idk which came first: 1) Uranus was affected by something. Then two scientists in separate countries mathematically calculated its position. 2)The same astronomer that mathematically calculated Neptune first proposed another possible planet Vulcan, and mathematical calculated its orbit[inside Mercury's, affecting Mercury's orbit]. Commented Feb 25, 2019 at 4:26
• @Max0815 They should be correct. I'll edit: "directly demonstrated" → "directly and correctly demonstrated"
– uhoh
Commented Feb 25, 2019 at 4:39
• We can determine the masses of planets if they have moons. For Mercury and Venus (pre space age) we had to deduce their masses from perturbations by other planets. I guess this would be among the earliest studies of this phenomenon. See:Determination of planetary mass and radius., Determination of Masses of Mercury and Venus from Observations of Five Minor Planets. Commented Feb 28, 2019 at 4:45
• @KeithMcClary Great! Then I think that citing the first mass deduction of Mercury and/or Venus (or even possibly of Earth) based on perturbations by other planets would be an excellent answer to my question!
– uhoh
Commented Feb 28, 2019 at 4:55
• It seems to be a complicated tale: google.ca/search?q=Leverrier+mass+venus , gsjournal.net/Science-Journal/… Someone on hsm.SE might know this. Commented Feb 28, 2019 at 5:28

My best guess: The late periapsis of 1P Halley in 1759.

In 1705, with the mathematical assistance of Issac Newton, Edmond Halley published Synopsis of the Astronomy of Comets which made the prediction that the comet observed in 1682 had previously been observed in 1531 and 1607 was the same object returning about every 76 years or so. He included a rough estimation of the gravitational effects of Jupiter and Saturn, and predicted it would return in 1758.

Halley's prediction of the comet's return proved to be correct, although it was not seen until 25 December 1758, by Johann Georg Palitzsch, a German farmer and amateur astronomer. It did not pass through its perihelion until 13 March 1759, the attraction of Jupiter and Saturn having caused a retardation of 618 days. This effect was computed prior to its return (with a one-month error to 13 April) by a team of three French mathematicians, Alexis Clairaut, Joseph Lalande, and Nicole-Reine Lepaute. The confirmation of the comet's return was the first time anything other than planets had been shown to orbit the Sun. It was also one of the earliest successful tests of Newtonian physics, and a clear demonstration of its explanatory power.

This predates the discovery of Uranus(1781) and Neptune (1846).

• Wow, thanks. Now that's going to be an interesting work to somehow find and read. This is great!
– uhoh
Commented Mar 2, 2019 at 1:25
• +1. Great contribution notovny, and welcome to Astronomy.SE :-) Commented Mar 2, 2019 at 3:22
• – uhoh
Commented Mar 11, 2019 at 4:02
• I'm not sure why I haven't accepted until now, but I'm accepting now! Thanks!
– uhoh
Commented Aug 26, 2019 at 14:36