<p>This idea would be a direct reduction from Newton's laws of motion.  In his <a href="https://en.wikisource.org/wiki/Page:Newton%27s_Principia_(1846).djvu/408" rel="nofollow noreferrer">Principia</a> he states "Hence the common centre of gravity of the earth, the sun, and all the planets, is to be esteemed the centre of the world".  So that would be the first evidence of the Sun moving outside of a geocentric universe.  Of course he wouldn't have known about Uranus and Neptune at the time.</p>

CC BY-SA 4.0
2019-09-01T20:41:50.757Z
Thanks for your answer, but as I also mentioned in [this comment](https://astronomy.stackexchange.com/questions/29742/first-observation-that-the-sun-and-jupiter-and-friends-move-around-a-common-ba/33227#comment61470_29742) I've asked for the *first observation* rather than the first realization.
uhoh
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2019-09-01T21:53:10.773Z
You'll want to update the question then or post a new one, this one specifically asks for __analysis of observations__.
Greg Miller
CC BY-SA 4.0
2019-09-01T23:44:45.667Z
**...that directly demonstrated that the Sun and the outer giant planets were moving around a common barycenter.** I have a hunch that the answer to my question will coincide with the first measurement of the mass of the Sun or more likely, the ratio of the masses of Jupiter and the Sun. If you'd like to specifically cite his [analysis of solar parallax](https://en.wikipedia.org/wiki/Solar_mass#History) then that could be an answer, though it seems he was so far off it was probably just wrong. But just saying "Newton said in a book that they go around a common center" isn't enough.
uhoh
CC BY-SA 4.0
2019-09-01T23:51:08.797Z
just fyi, while the bounty expires in about 15 hours, there's a further 24 hour "grace period".
uhoh
CC BY-SA 4.0
2019-09-02T01:29:19.773Z
"Analysis of observations" and "Observations" are different things.  Newtons entire Principia is about showing how his laws of motion fit to prior observations, just one conclusion of which is the solar system barrycenter.  It sounds like you're looking for something else, so good luck.
Greg Miller
CC BY-SA 4.0
2019-09-01T20:04:16.850Z
2019-09-01T20:04:16.850Z
Greg Miller
<p>Answers to the question <a href="https://astronomy.stackexchange.com/q/4834/7982">How did Kepler determine the orbital period of Mars?</a> describing careful observations centuries ago got me thinking.</p>

<p>What was the first analysis of observations that directly demonstrated that the Sun and the outer giant planets were moving around a common barycenter rather than all planets rotating around a fixed Sun?</p>

<p>I am not sure if <a href="https://astronomy.stackexchange.com/q/29741/7982">First observation that the movement of a planet or asteroid in its orbit was affected by another planet?</a> is a completely separate question, or if this confirmation happened all at once, but I've currently asked it separately.</p>

CC BY-SA 4.0
2019-02-25T04:33:03.283Z
I don't think so. Jupiter shouldn't be that massive to affect the Sun. It is only in rather large planet and small star systems where the affect can be noticed. I would rather think that the planets orbit the Sun in a point inside the star rather than an external barycenter.
Max0815
CC BY-SA 4.0
2019-02-25T04:38:03.903Z
Wait ah after some equations and using Wolfram Alpha I think you are right! Jupiter orbit at a barycenter! The barycenter for Jupiter is 1.07 solar radiuses from the center.
Max0815
CC BY-SA 4.0
2019-02-25T04:43:07.510Z
@Max0815 The Sun's orbit is a swirly pattern. There's a nice plot somewhere in Wikipedia and in several different answers here and other SE sites, but here's some plots I made: https://astronomy.stackexchange.com/a/20019/7982
uhoh
CC BY-SA 4.0
2019-02-25T04:43:29.180Z
Then, I think your statement "the Sun **and the outer giant planets** were moving around a common barycenter rather than all planets rotating around a fixed Sun?" is incorrect. Only Jupiter is massive enough to have a barycenter. The next massive planet is Saturn, which is 1/3 the mass of Jupiter. This means the "barycenter" for it is .356 solar radii which isn't a barycenter at all.
Max0815
CC BY-SA 4.0
2019-02-25T04:44:17.940Z
oh, ok. its late. I'll read thru your plots and see if I can come up with an answer after some research tomorrow.
Max0815
CC BY-SA 4.0
2019-02-25T04:46:45.033Z
@Max0815 any statement about things moving in orbits is incorrect so some degree, this is understood in orbital mechanics. Even a [non-keplerian, non-newtonian n-body numerical simulation of the solar system](https://space.stackexchange.com/a/23409/12102) doesn't include gravitational effects from things *outside* the solar system. As soon as you say the word "orbit" you've started down the rabbit hole of approximations.
uhoh
CC BY-SA 4.0
2019-02-25T06:45:26.663Z
Hey @Max0815 Here's the swirly diagram of the solar system barycentre that uhoh mentioned. https://astronomy.stackexchange.com/a/28036/16685
PM 2Ring
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2019-02-26T20:14:50.383Z
@uhoh I'll need to look more into this. More complicated than I thought xD.
Max0815
CC BY-SA 4.0
2019-02-27T23:56:26.677Z
@uhoh I don't know anything about this topic, and I can't to seem to find a source on this topic other than articles saying the barycenter is 1.07 solar radii.
Max0815
CC BY-SA 4.0
2019-02-28T00:04:11.310Z
@Max0815 The 1.07 is only for the Sun-Jupiter system. The other large planets (Saturn, Uranus, Neptune) are not as heavy as Jupiter but they are farther out and the combined motion moves the Sun almost 2 solar radii at maximum.
uhoh
CC BY-SA 4.0
2019-02-28T20:01:33.110Z
Not the same question, and no mention of the first measurement, but related:   https://physics.stackexchange.com/questions/258539/error-measurement-barycenter-of-the-solar-system-nasa-data   I would suggest, but I can't say for certain, that because Newton worked out the mathematics of the two body problem, and combined with difficulty in directly measuring this, that direct observation of a barycenter may not have been a priority. Probably the easiest place to observe it would be Jupiter and it's moons.  Jupiter tugs on the Earth as well as the sun, so that's more of a 3 body or tidal effect.
userLTK
CC BY-SA 4.0
2019-08-27T04:24:12.093Z
Wouldn't any "analysis of observations" of planetary motions involve use of Newton's theory of gravity (what else?). But Newton's theory implies the barycenter. The only way to have a "fixed Sun" is if its inertial mass is infinite (or very large compared to its gravitational mass). I doubt that anyone ever proposed a "fixed Sun" theory (although it would have been a test of the gravitational-inertial mass equivalence).
Keith McClary
CC BY-SA 4.0
2019-08-27T04:34:21.717Z
@KeithMcClary This is why I've asked for the first *observation*, and not "when was it realized that...". The data and analysis need to be careful enough to show that the Sun moves around a system barycenter. So the ratio of the Sun's mass to that of Jupiter will be in there somewhere, meaning that the first time that ratio was measured is likely to also be the answer to this question.
uhoh
CC BY-SA 4.0
2020-05-28T08:19:19.720Z
@antispinwards all one has to do is to show that the big planets are moving the Sun around measurably. Whenever that was first shown, that's the answer to my question.
uhoh
CC BY-SA 4.0
2020-05-29T10:52:56.147Z
@antispinwards In orbits, movement involves *acceleration* and once that happens we can no longer dismiss the topic as quibbling. To your question "...relative to what?" my answer is *any inertial frame*.
uhoh
CC BY-SA 4.0
2020-05-29T11:07:36.673Z
@antispinwards I didn't say the SS Bary. is an inertial frame. However the Sun's acceleration due to the big planets varies on an observational timescale; years and decades. *Variation in acceleration of the Sun due to the interstellar gravity field* would be much smaller on the same time scale. I really am not quibbling, one is much bigger than the other.
uhoh
<the-sun><solar-system><history>
First observation that the Sun and Jupiter (and friends) move around a common barycenter?
uhoh
# First observation that the Sun and Jupiter (and friends) move around a common barycenter?

(Asked by: username_0 on 2019-02-25)

Answers to the question [How did Kepler determine the orbital period of Mars?](https://astronomy.stackexchange.com/q/4834/7982) describing careful observations centuries ago got me thinking.

What was the first analysis of observations that directly demonstrated that the Sun and the outer giant planets were moving around a common barycenter rather than all planets rotating around a fixed Sun?

I am not sure if [First observation that the movement of a planet or asteroid in its orbit was affected by another planet?](https://astronomy.stackexchange.com/q/29741/7982) is a completely separate question, or if this confirmation happened all at once, but I've currently asked it separately.

**Tags:** the-sun, solar-system, history

> **Comments:**
> **username_1**: I don't think so. Jupiter shouldn't be that massive to affect the Sun. It is only in rather large planet and small star systems where the affect can be noticed. I would rather think that the planets orbit the Sun in a point inside the star rather than an external barycenter.  
> **username_1**: Wait ah after some equations and using Wolfram Alpha I think you are right! Jupiter orbit at a barycenter! The barycenter for Jupiter is 1.07 solar radiuses from the center.  
> **username_0**: @username_1 The Sun's orbit is a swirly pattern. There's a nice plot somewhere in Wikipedia and in several different answers here and other SE sites, but here's some plots I made: https://astronomy.stackexchange.com/a/20019/7982  
> **username_1**: Then, I think your statement "the Sun **and the outer giant planets** were moving around a common barycenter rather than all planets rotating around a fixed Sun?" is incorrect. Only Jupiter is massive enough to have a barycenter. The next massive planet is Saturn, which is 1/3 the mass of Jupiter. This means the "barycenter" for it is .356 solar radii which isn't a barycenter at all.  
> **username_1**: oh, ok. its late. I'll read thru your plots and see if I can come up with an answer after some research tomorrow.  
> **username_0**: @username_1 any statement about things moving in orbits is incorrect so some degree, this is understood in orbital mechanics. Even a [non-keplerian, non-newtonian n-body numerical simulation of the solar system](https://space.stackexchange.com/a/23409/12102) doesn't include gravitational effects from things *outside* the solar system. As soon as you say the word "orbit" you've started down the rabbit hole of approximations.  
> **username_2**: Hey @username_1 Here's the swirly diagram of the solar system barycentre that username_0 mentioned. https://astronomy.stackexchange.com/a/28036/16685  
> **username_1**: @username_0 I'll need to look more into this. More complicated than I thought xD.  
> **username_1**: @username_0 I don't know anything about this topic, and I can't to seem to find a source on this topic other than articles saying the barycenter is 1.07 solar radii.  
> **username_0**: @username_1 The 1.07 is only for the Sun-Jupiter system. The other large planets (Saturn, Uranus, Neptune) are not as heavy as Jupiter but they are farther out and the combined motion moves the Sun almost 2 solar radii at maximum.  
> **username_3**: Not the same question, and no mention of the first measurement, but related:   https://physics.stackexchange.com/questions/258539/error-measurement-barycenter-of-the-solar-system-nasa-data   I would suggest, but I can't say for certain, that because Newton worked out the mathematics of the two body problem, and combined with difficulty in directly measuring this, that direct observation of a barycenter may not have been a priority. Probably the easiest place to observe it would be Jupiter and it's moons.  Jupiter tugs on the Earth as well as the sun, so that's more of a 3 body or tidal effect.  
> **username_4**: Wouldn't any "analysis of observations" of planetary motions involve use of Newton's theory of gravity (what else?). But Newton's theory implies the barycenter. The only way to have a "fixed Sun" is if its inertial mass is infinite (or very large compared to its gravitational mass). I doubt that anyone ever proposed a "fixed Sun" theory (although it would have been a test of the gravitational-inertial mass equivalence).  
> **username_0**: @KeithMcClary This is why I've asked for the first *observation*, and not "when was it realized that...". The data and analysis need to be careful enough to show that the Sun moves around a system barycenter. So the ratio of the Sun's mass to that of Jupiter will be in there somewhere, meaning that the first time that ratio was measured is likely to also be the answer to this question.  
> **username_0**: @antispinwards all one has to do is to show that the big planets are moving the Sun around measurably. Whenever that was first shown, that's the answer to my question.  
> **username_0**: @antispinwards In orbits, movement involves *acceleration* and once that happens we can no longer dismiss the topic as quibbling. To your question "...relative to what?" my answer is *any inertial frame*.  
> **username_0**: @antispinwards I didn't say the SS Bary. is an inertial frame. However the Sun's acceleration due to the big planets varies on an observational timescale; years and decades. *Variation in acceleration of the Sun due to the interstellar gravity field* would be much smaller on the same time scale. I really am not quibbling, one is much bigger than the other.  

---

## 1 answers

### Answer by username_5 on 2019-09-01. Score: 2 | Accepted answer

This idea would be a direct reduction from Newton's laws of motion. In his [Principia](https://en.wikisource.org/wiki/Page:Newton%27s_Principia_(1846).djvu/408) he states "Hence the common centre of gravity of the earth, the sun, and all the planets, is to be esteemed the centre of the world". So that would be the first evidence of the Sun moving outside of a geocentric universe. Of course he wouldn't have known about Uranus and Neptune at the time.

> **Comments:**
> **username_0**: Thanks for your answer, but as I also mentioned in [this comment](https://astronomy.stackexchange.com/questions/29742/first-observation-that-the-sun-and-jupiter-and-friends-move-around-a-common-ba/33227#comment61470_29742) I've asked for the *first observation* rather than the first realization.  
> **username_5**: You'll want to update the question then or post a new one, this one specifically asks for __analysis of observations__.  
> **username_0**: **...that directly demonstrated that the Sun and the outer giant planets were moving around a common barycenter.** I have a hunch that the answer to my question will coincide with the first measurement of the mass of the Sun or more likely, the ratio of the masses of Jupiter and the Sun. If you'd like to specifically cite his [analysis of solar parallax](https://en.wikipedia.org/wiki/Solar_mass#History) then that could be an answer, though it seems he was so far off it was probably just wrong. But just saying "Newton said in a book that they go around a common center" isn't enough.  
> **username_0**: just fyi, while the bounty expires in about 15 hours, there's a further 24 hour "grace period".  
> **username_5**: "Analysis of observations" and "Observations" are different things.  Newtons entire Principia is about showing how his laws of motion fit to prior observations, just one conclusion of which is the solar system barrycenter.  It sounds like you're looking for something else, so good luck.  

---

