<p>Newton explained the motions of planets in the solar system in Principia in 1687.</p>

<p>This amongst many other things "defines the very slow motion of the Sun relative to the solar-system barycenter;" (<a href="https://en.m.wikipedia.org/wiki/Philosophi%C3%A6_Naturalis_Principia_Mathematica" rel="noreferrer">https://en.m.wikipedia.org/wiki/Philosophiæ_Naturalis_Principia_Mathematica</a> ).</p>

<p>Since Newton came up with the ideas of gravity and barycentres, surely this is the answer? (Though, I note there is some debate that the inverse square law may have been around and discussed during the previous decade).</p>

<p>Ideas that the Sun <em>moved</em> were of course commonplace before then.</p>

CC BY-SA 4.0
2018-10-17T07:36:03.670Z
Not when the theory was discovered, asking more for when the actual motions were mapped. Aristarchus and so on had detailed the theory as well. Today, online, I can see detailed maps of the suns orbit around the barycenter, when did that begin to enter the scene?
pol0
CC BY-SA 4.0
2018-10-18T22:05:58.447Z
You should ask that then @pol0. Currently your question doesn't say that
Rory Alsop
CC BY-SA 4.0
2018-10-17T06:14:50.303Z
2018-10-17T06:25:12.087Z
2018-10-17T06:25:12.087Z
ProfRob
<p>It's commonly known that the center of gravity of our solar system is not the suns axis, and, that the same goes for other orbital systems like Pluto and Charon, and so on. When was it discovered that our sun has an orbit around a barycenter?</p>

CC BY-SA 4.0
2018-10-17T04:34:37.900Z
the question isn't when it was discovered or entered public consciousness that planets revolve around the sun, it is a bit of a leap to go from that to that the sun is revolving a barycenter of the solar system as a whole
pol0
CC BY-SA 4.0
2018-10-17T04:36:28.313Z
I've seen August Möbius Der barycentrische Calcul from 1827 attributed for the concept of a barycenter, but what I'm looking for is when it became known, or, contemplated about, that our sun orbited a barycenter of the solar system as a whole, when that theory had begun to be applied to our solar system and discussed and talked about in the scientific literature
pol0
CC BY-SA 4.0
2018-10-17T04:48:56.317Z
Aristarchus did as well. When did it became widely considered, data collected to prove it, and so on, the diameter and shapes of the orbits mapped? I'm looking at it from a history of ideas perspective to correlate with other ideas that developed during the 19th century mainly.
pol0
CC BY-SA 4.0
2018-10-17T05:21:05.073Z
It's inherent in Newtonian gravitation, but it's not exactly easy to determine the motion of the barycenter relative to the Sun without precision instruments.
PM 2Ring
CC BY-SA 4.0
2018-10-17T05:26:48.183Z
The Greeks had developed orbital models as well. When was it, empirically, discovered that our sun orbits a barycenter, in a way where it was not just theory but people knew that it was so?
pol0
CC BY-SA 4.0
2018-10-17T06:35:57.833Z
@barrycarter isn't Kepler first law incompatible with your statement? Or is "the Sun at one focus" not what Kepler actually wrote (genuine question)?
ProfRob
CC BY-SA 4.0
2018-10-17T07:55:17.860Z
Please add what information you already have about this question. As far as I know (which may be little indeed) Aristarchus wrote about the Earth revolving around the Sun, not a barycentre. And to prevent further answers that you don't want, please clarify your question. It seems you are actually asking when observations became available that were capable of being interpreted as motion around the barycentre.
ProfRob
CC BY-SA 4.0
2018-10-17T08:06:29.650Z
@barrycarter To clarify - the planets do *not* move in elliptical orbits with the Sun at one focus. The barycentre is at the focus. So if Kepler wrote that it was the Sun at the focus, then he did not propose that the Sun orbits a barycentre.
ProfRob
CC BY-SA 4.0
2018-10-17T18:52:37.593Z
@barrycarter I don't see how you extrapolate that from the statement you quote. The solar system barycentre is nowhere near the midpoint of the two foci of Mercury's elliptical orbit and the disproof of your version is easily seen by considering two similar mass stars in an eccentric orbit (e.g. https://en.wikipedia.org/wiki/Binary_star#/media/File:Orbit5.gif ) . Kepler's first law is *approximately* true if $m \ll M$. It is exactly true if you replace "Sun" with "barycentre".
ProfRob
CC BY-SA 4.0
2018-10-17T19:57:34.497Z
@barrycarter Thinking...   The best way to think about a small planet's orbit is as an orbit with the Sun at the focus with a secondary (smaller amplitude) orbit with a 12-year period around the Sun-Jupiter barycentre superimposed. I am withdrawing my suggestion that if you modelled Mercury's orbit as an approximate ellipse that the SSB would be the best focus. This would be exactly true for 2-bodies, is approximately true for Jupiter, but is not true for >2 bodies where a third body is much more massive.
ProfRob
CC BY-SA 4.0
2018-10-19T12:02:57.960Z
@uhoh I think you have misinterpreted. It is quite the opposite. Mercury has an 88 day orbit essentially with the centre of the Sun at one focus (actually the Sun-Mercury barycentre). If you look on longer timescales the Sun then orbits the solar system barycentre.
ProfRob
CC BY-SA 4.0
2018-10-19T12:08:21.040Z
@RobJeffries I got excited and somehow missed the word "withdrawing" in the sentence. I'll now do some withdrawing myself ;-)
uhoh
<solar-system>
When did we discover that our sun does not orbit its own axis but a barycenter?
pol0
# When did we discover that our sun does not orbit its own axis but a barycenter?

(Asked by: username_0 on 2018-10-17)

It's commonly known that the center of gravity of our solar system is not the suns axis, and, that the same goes for other orbital systems like Pluto and Charon, and so on. When was it discovered that our sun has an orbit around a barycenter?

**Tags:** solar-system
> **Comments:**
> **username_0**: the question isn't when it was discovered or entered public consciousness that planets revolve around the sun, it is a bit of a leap to go from that to that the sun is revolving a barycenter of the solar system as a whole  
> **username_0**: I've seen August Möbius Der barycentrische Calcul from 1827 attributed for the concept of a barycenter, but what I'm looking for is when it became known, or, contemplated about, that our sun orbited a barycenter of the solar system as a whole, when that theory had begun to be applied to our solar system and discussed and talked about in the scientific literature  
> **username_0**: Aristarchus did as well. When did it became widely considered, data collected to prove it, and so on, the diameter and shapes of the orbits mapped? I'm looking at it from a history of ideas perspective to correlate with other ideas that developed during the 19th century mainly.  
> **username_1**: It's inherent in Newtonian gravitation, but it's not exactly easy to determine the motion of the barycenter relative to the Sun without precision instruments.  
> **username_0**: The Greeks had developed orbital models as well. When was it, empirically, discovered that our sun orbits a barycenter, in a way where it was not just theory but people knew that it was so?  
> **username_2**: @barrycarter isn't Kepler first law incompatible with your statement? Or is "the Sun at one focus" not what Kepler actually wrote (genuine question)?  
> **username_2**: Please add what information you already have about this question. As far as I know (which may be little indeed) Aristarchus wrote about the Earth revolving around the Sun, not a barycentre. And to prevent further answers that you don't want, please clarify your question. It seems you are actually asking when observations became available that were capable of being interpreted as motion around the barycentre.  
> **username_2**: @barrycarter To clarify - the planets do *not* move in elliptical orbits with the Sun at one focus. The barycentre is at the focus. So if Kepler wrote that it was the Sun at the focus, then he did not propose that the Sun orbits a barycentre.  
> **username_2**: @barrycarter I don't see how you extrapolate that from the statement you quote. The solar system barycentre is nowhere near the midpoint of the two foci of Mercury's elliptical orbit and the disproof of your version is easily seen by considering two similar mass stars in an eccentric orbit (e.g. https://en.wikipedia.org/wiki/Binary_star#/media/File:Orbit5.gif ) . Kepler's first law is *approximately* true if $m \ll M$. It is exactly true if you replace "Sun" with "barycentre".  
> **username_2**: @barrycarter Thinking...   The best way to think about a small planet's orbit is as an orbit with the Sun at the focus with a secondary (smaller amplitude) orbit with a 12-year period around the Sun-Jupiter barycentre superimposed. I am withdrawing my suggestion that if you modelled Mercury's orbit as an approximate ellipse that the SSB would be the best focus. This would be exactly true for 2-bodies, is approximately true for Jupiter, but is not true for >2 bodies where a third body is much more massive.  
> **username_2**: @uhoh I think you have misinterpreted. It is quite the opposite. Mercury has an 88 day orbit essentially with the centre of the Sun at one focus (actually the Sun-Mercury barycentre). If you look on longer timescales the Sun then orbits the solar system barycentre.  
> **username_3**: @RobJeffries I got excited and somehow missed the word "withdrawing" in the sentence. I'll now do some withdrawing myself ;-)  

---

## 1 answers

### Answer by username_2 on 2018-10-17. Score: 5

Newton explained the motions of planets in the solar system in Principia in 1687.

This amongst many other things "defines the very slow motion of the Sun relative to the solar-system barycenter;" ([https://en.m.wikipedia.org/wiki/Philosophiæ\_Naturalis\_Principia\_Mathematica](https://en.m.wikipedia.org/wiki/Philosophi%C3%A6_Naturalis_Principia_Mathematica) ).

Since Newton came up with the ideas of gravity and barycentres, surely this is the answer? (Though, I note there is some debate that the inverse square law may have been around and discussed during the previous decade).

Ideas that the Sun *moved* were of course commonplace before then.

> **Comments:**
> **username_0**: Not when the theory was discovered, asking more for when the actual motions were mapped. Aristarchus and so on had detailed the theory as well. Today, online, I can see detailed maps of the suns orbit around the barycenter, when did that begin to enter the scene?  
> **username_4**: You should ask that then @pol0. Currently your question doesn't say that  

---

