Talk:Barycenter (astronomy)

Comments

"When the two bodies are of similar masses ... the barycenter will be located outside of either of them and both bodies will follow an orbit around it. This is the case for Pluto and Charon, Jupiter and the Sun..."

I just crunched the numbers, and the barycenter as calculated for just the two objects Sol & Jupiter gets me a barycenter that is about 87% of Sol's diameter (i.e., about 13% of the way inside Sol's outermost layer). I used the following values:

r_tot = 7.783x10⁸ km (mean distance between Sol and Jupiter)

m₁ = 1.899×10²⁷ kg (mass of Jupiter)

m₂1.9891×10³⁰ kg (mass of Sol).

This results in Jupiter being 777 557 663.3 km from the barycenter, and Sol being 742 336.7 km from the barycenter. Is the above-quoted claim incorrect, or is my math misleading due to ignoring the other bodies in the Solar System?

The barycenter is more than 50% of the diameter of the Sun away from the center, so outside the Sun.--Patrick 12:21, 21 October 2005 (UTC)

You are correct the Sun-Jupiter Barycenter is outside the surface of the Sun. It is about 107 % of the Sun's Radius.63.225.17.34 (talk) 20:12, 24 February 2016 (UTC)

Jupiter is the Only Planet with enough mass at its distance to move that Pairs Barycenter outside the Sun's Radius. 63.225.17.34 (talk) 20:16, 24 February 2016 (UTC)

Merge? (2005)

I think this article should be merged with center of mass. Physically this article gives no new info than center of mass. 193.52.24.125 18:42, 23 October 2005 (UTC)

I have just merged the 2. 193.52.24.125 17:46, 24 October 2005 (UTC)

Merge articles (2015)

I proposed to merge Barycentric coordinates (astronomy) into Barycenter. They seem to be redundant in large parts. In addition, there is already a (generic) article Center of mass, and I find it confusing to have three different link-targets used in astronomy articles for the word "barycenter". In case I'm completely wrong about my proposal, please consider to remove the hatnotes from the articles. Thx. -- Cheers, Rfassbind -talk 20:40, 28 June 2015 (UTC)

Support: Just from the standpoint of general article writing and construction, we've got a stub here and related material there, which altogether makes a data volume appropriate for one article. The only reason I could see for holding off would be if someone thought the merged article might become too long in the future. Evensteven (talk) 21:33, 28 June 2015 (UTC)

Support: Makes sense to merge these, the former is a subtopic of the latter and the latter is just past stub. --JorisvS (talk) 09:17, 29 June 2015 (UTC)

I began to merge the articles now. I'll try to include as much as possible from both articles, except for any obvious redundancies, since it's much easier to remove content later on, rather than to add any specific detail I may have left out during the merger. Your contribution is very much appreciated as soon as I have removed the {{Under construction}} template. -- Cheers, Rfassbind -talk 08:48, 9 July 2015 (UTC)

Comment This article title, as it stands now, is misleading. It talks about barycentric coordinates only in the astronomical, gravitational context and completely ignores the likely more common simplex-based coordinate system used in lots of scientific contexts. The simplex-based coordinate system is discussed in Barycentric coordinate system. Consequently, I think either this article needs a balanced presentation of the different types of barycentric coordinate systems or it needs to be moved to Barycenter (astronomy), or better yet, Barycentric coordinates (astronomy). --Mark viking (talk) 21:06, 9 July 2015 (UTC)

Thx for the info. As far as I can see, the article "Barycenter" has always been written in an astronomical / gravitational context. At least that's what the first version of March 2003 tells me. Unfortunately, I do not understand why, after more than twelve years, the article's title has now become misleading, just hours after I inserted additional content from "Barycentric coordinates (astronomy)". Maybe someone more experienced than I am should figure out what to do, since I'm obviously not the right guy for this. -- Rfassbind -talk 02:44, 10 July 2015 (UTC)

Sorry, I don't mean to sound harsh. I didn't really pay attention the barycenter article until you did the merge. You're correct that the barycenter article had the problem I complained about before the merge, too. So I don't think you did anything to make it worse in terms of balance. It is just that if the consensus is that this is to be the article in WP that is going to discuss the astronomical concept of barycentric coordinates, it has to be disambiguated from the other common type of barycentric coordinates. I personally don't think that the astronomical concept is dominant over the simplex based concept, so I suggested adding (astronomy) to the title to make it clear that this is only about the astronomical type of barycentric coordinate system. --Mark viking (talk) 04:05, 10 July 2015 (UTC)

Well, the merge is done, and that's probably a good thing in itself. Mark brings up what's really a different issue, which is "what is the right title for this article?" Perhaps that's a separate proposal that should now be considered. I don't see it affecting anything that was done in the merge. Evensteven (talk) 04:14, 10 July 2015 (UTC)

What's wrong with title as it is? --JorisvS (talk) 08:54, 10 July 2015 (UTC)

See Mark's comment above. I'm not making a name change proposal myself, but I was suggesting that one might be the way to go if it is enough of an issue. I'll need to let Mark or others decide that. Evensteven (talk) 14:28, 10 July 2015 (UTC)

Not so much, else I wouldn't have asked. I see him complain about it, but it doesn't make it clear to me what is supposed to the problem with the current title. --JorisvS (talk) 17:33, 10 July 2015 (UTC)

Not clear to me either, although that's not a reason to believe there isn't a problem. However, it's up to the person who recognizes one to bring it up, and I'm not the one who can do it. Evensteven (talk) 18:56, 10 July 2015 (UTC)

I can't see it. That's why I asked the question. @Mark viking: Maybe pinging will help. --JorisvS (talk) 19:10, 10 July 2015 (UTC)

Have patience; I am busy in real life and have not had a chance to reply until lunch time. Let me try to be more explicit in my assertion. The article title "Barycenter" promises an article on the general concept of a barycenter. But the current article content only discusses the astronomical use of the term. Other uses of the term, IMO even more commonplace, include the simplex-based coordinate system in Barycentric coordinate system, and barycenter as a synonym for the centroid concept in geometry, engineering, and statistics. But these other uses are barely mentioned in this article. Thus as it stands, the article is unbalanced and fails neutrality (one of WP's five pillars) through lack of due weight to the different uses of the term and concept in different fields of study.

How best to fix this problem? Two possibilities are

• Move the article to Barycenter (astronomy). Then it is clear that the article is just about the astronomical concept. Hatnotes can direct readers to other uses of the term.
• Expand the article to include sections with due weight regarding other uses, such as the centroid and the traditional barycentric coordinates.

The first option is the easier of the two to implement and can be thought of as just restoring the (astronomy) tag of the original article Barycentric coordinates (astronomy). I hope this makes it clearer. --Mark viking (talk) 20:06, 10 July 2015 (UTC)

I support your first option. Dbfirs 13:13, 11 July 2015 (UTC)

Agreed. The first option is reasonable. Evensteven (talk) 17:34, 11 July 2015 (UTC)

Please open a new section for any new proposals other than the already accomplished merger of the two articles mentioned in the first post. Thx, -- Rfassbind -talk 18:15, 11 July 2015 (UTC)

Barycenter Edits

The location of the Earth-Moon Barycenter is based on 1 Plus (the Ratio of the Mass of the Earth divided by the of the mass of the Moon), and then Multiplied by the Average distance between the two. That ratio ( to a ridiculous number of digits) is 81.30059122 . Adding 1 gives ( 1 / 82.30059122 ) X 384,401 km = 4670.695487 km ( also to a ridiculous number of digits ). Rounding would gives Earth to E-M BC = 4670.7 km and Moon to E-M BC = 379,730.3 km for a total of 384,401 km. The number ( 81.30059122 ) is gradually increasing as the Earth gains mass, very slowly, but, faster than the Moon gains mass. The change in mass, and the change in mass ratio gradually moves the Moon to a higher orbit, and the Earth to a lower orbit relative to the E-M BC. The total change is a gross increase of approximately 42.36 mm per year, but the net change is only measured at about 38.2 mm per year ( McDonald Observatory, Texas: Lunar Laser Ranging ). The difference is the net increase in the Radius of the Earth ( 4.16 +/- 0.01 mm per year ).

The change in the distance is about 1 part in 9.0888 Billion, which is 1 part in twice the age of the Earth.

The Radius of the Earth is actually about 6372.4567 Km at the tilt angle of 23.491 degrees. The 6378 is an Equatorial Radius of the Earth. If a planet had uniform density, and was a sphere, ( both are not true of the Earth ), then the equal force tilt angle would be close to 23 degrees, 19 minutes and 39.3 seconds of tilt relative to the Force applied by the Sun. This would be the tilt angle radius that would represent the mass of the Planets, which in turn would apply to the mass ratio between co-orbiting planets, and thus that ratio of r1 and R2.

A large Mass multiplied by a small radius is equal to a Large radius multiplied by a smaller mass. This determines both the Mass Ratio, and/or the distance Ratio. In the case of the Earth and Moon it is the same number ( 81.30059122 ). Most would round this to 81.3 which would change the Earth to E-M BC to 4670.72904 KM, which would still round down to 4670.7 km. 63.225.17.34 (talk) 21:22, 24 February 2016 (UTC)

The First Figure in the Atricle

The first figure in the article is with extremely low resolution, and I suggest to replace it with a better one. 213.8.204.61 (talk) 08:48, 20 April 2016 (UTC)

Here's a candidate: [1] Do you know of a better image? Certes (talk) 10:57, 20 April 2016 (UTC)

Barycentre perihelions?

To make the data useful and practical, it is necessary to have the date/time of barycentric perihelion, and the rate of apsidal precession. Otherwise it reads like a textbook on theory and it is impossible to visualise the reality of it. Bards (talk) 13:26, 20 August 2016 (UTC)

That's a very good remark. Please go ahead and make the data useful and practical. Thank you, Rfassbind – talk 15:38, 20 August 2016 (UTC)

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Semi-major axis definition?

Does the semimajor axis refer to the distance between two orbiting bodies or the distance from a body to the barycenter? According to this article it is the distance from a body to the barycenter (assuming circular orbits). This is inconsistent with other wiki articles. E.g. the Moon article lists both the Earth-Moon average distance and semimajor axis as 384400 km. But according to this article, the Moon's semimajor axis should be 379730km (and the Earth's 4670km). Also wiki lists Jupiter having a semimajor axis of 7.783x10⁸ km rather than 7.776x10⁸ km as suggested by Patrick above. Gigarose (talk) 11:34, 15 April 2017 (UTC)

After reviewing information in the Semi-major_and_semi-minor_axes article - particularly the equation for orbital period - I've concluded that 'semi-major axis' refers to the distance between orbiting bodies and not the distance from a body to the barycenter. This article uses the separation distance definition, but also defines it according to the barycenter distance, which might be wrong. Gigarose (talk) 14:01, 19 April 2017 (UTC)

The ephemerides of the Moon and planets used by most of the world is described in Explanatory Supplement to the Astronomical Almanac, Chapter 8: Ephemerides of the Sun, Moon, and Planets, 3rd edition, 2013. This is an iterative calculation of this n-body problem. The daily positions of all planets are calculated relative to the barycenter of the Solar System, page 4. However, elliptical dimensions such as their semimajor axis is not specified because ellipses are not used. Instead, their Keplerian elements are curve fitted to the results giving a lower accuracy relative to the center of the Sun (Heliocentric), page 28. The distance from the center of the Sun to the center of Jupiter is specified as 5.20288700 au −0.00011607 au/cty for the mean ecliptic and equinox of J2000 valid for 1850–2050, where au = astronomical unit = 149597870.691 km, and cty is a Julian century of 36525 SI days. Thus at J2000 (2000 January 1 noon T_epm ≅ Barycentric Dynamical Time), the distance from Jupiter to the Sun was 7.78340817 × 10⁸ km. — Preceding unsigned comment added by Joe Kress (talk • contribs) 15:16, 24 April 2017 (UTC)‎

Two bodies orbiting their common barycenter in elliptic orbits??

The Gallery's fifth image shows two bodies orbiting their common barycenter in elliptic orbits. Is that true? According to Isaac Newton's Principia (Book I Corol. 4 to the laws of motion; Sect. 1 "To find centripetal forces", Prop. 1) the orbits around a barycenter to which the common central force is directed must be circular in the absence of another force, as is correctly shown in the first four images.84.144.158.99 (talk) 07:54, 11 May 2017 (UTC)

Did Newton say that? Was there not an additional condition? The general two-body problem allows circular, elliptical, parabolic and hyperbolic orbits. So, yes, the fifth image is correct.

Newton's theory of the common center of gravity (Principia Book I Corol. iv to the laws)

Why is Newton's theory of the common center of gravity ignored in this article? See Principia Book I Corol. IV to the laws of motion. Some statements directly oppose Newton's theory. What are the scientific basics of this article's assertions? Ed Dellian84.170.236.180 (talk) 10:01, 4 June 2017 (UTC)

Which statements contradict Newton's theory? Dbfirs

barycenter formula

mass1 / mass2 * distance * .5 = barycenter distance = distance between the centers of the 2 objects mass1 = smaller of the 2 objects mass2 = larger of the 2 objects barycenter= ration of mass between the 2 objects * distance divided ny 2 it doesn't just just looks easier to understand than the formula presented. computers can run it faster — Preceding unsigned comment added by Jonathan scott james (talk • contribs) 07:45, 31 October 2020 (UTC)

The last paragraph starts with "For objects at such high eccentricity". I guess you mean "For objects with such large semi-major axes"?

Suggestion re the animations

The animations of various bodies rotating about their center of gravity would be improved if it were clear that the bodies are in fact rotating.

Because the bodies have no decoration but are instead a uniform color, this is not clear. One's instinctive reaction is to perceive especially the large body as simply translating in space but not rotating. In other words, it can easily be an optical illustion.

Putting some kind of (non rotationally symmetric) design or decoration on the bodies will eliminate this illusion.

I hope the original contributor can do this.

Additional comment: This subject should not be classified as astronomy: It is physics.

Very basic newtonian physics, in fact.