Talk:Orbit

Understanding Orbits Sections

In the Understanding Orbits section I've described a "range of" parabolic and hyperbolic orbits.

Is that accurate?

Or -- from a given firing height, with a given mass -- is there:

• only one possible parabolic orbit and a range of possible hyperbolic orbits, or,
• a range of possible parabolic orbits and only one possible hyperbolic orbit, or,
• only one possible parabolic orbit and one possible hyperbolic orbit?

Note both a parallel firing direction, and the "tilted cannon" discussed in the next Talk subject.

An orbit is not a path around a point in space

Wikipedia currently gives the definition of orbit as follows: "In physics, an orbit is the gravitationally curved path of an object around a point in space..."

It is unclear what "around" means in this definition, but any meaning of "around" seems incorrect. If "around" is meant to imply that an orbit is a path traversing all 360° of arc surrounding a point, that implies that hyperbolic orbits are not orbits, and that is incorrect. If "around" is meant to imply that an orbit is a path which forms a concavity containing at least one point, then that contributes nothing to the definition. And if "around" is meant to imply that an orbit has a special affinity with a specific point, the barycenter, then that is a clear case of map/territory confusion -- orbits are in no way related to barycenters; only our models of orbits are related to barycenters.

I am stumped to think of a way that "around a point in space" aptly describes an orbit. I can see that one of the sources cited for Wikipedia's definition is the Encyclopædia Britannica, which describes an orbit as a path "around an attracting centre of mass". Perhaps this is the source of the problem -- Encyclopædia Britannica got the definition wrong, and the error was replicated here on Wikipedia.

-TC 47.142.130.130 (talk) 23:17, 10 May 2017 (UTC)

What would you suggest in place of the current wording? - MrOllie (talk) 23:38, 10 May 2017 (UTC)

How about just removing the "point in space" bit. For instance: "In physics, an orbit is the gravitationally curved trajectory of an object."

From what I can tell, the thing which truly distinguishes an orbit from any other type of trajectory is that an orbit is generated by gravitational forces only. That might suggest a definition something like this: "In physics, an orbit is the trajectory of an object which is subject primarily to gravitational forces." Could we nudge the definition in that direction?

-TC 47.142.130.130 (talk) 20:20, 21 July 2017 (UTC)

This seems to me to be a silly subdiscussion. But the major point that the Wikipedia definition is WRONG is well founded. The problem is the lack of context. Orbits in general can be open (hyperbolic) or closed (periodic, elliptical, circular). (Parabolic orbits aren't generally found in nature, and of course in real systems actual orbital paths are never precisely in a single plane (nor are they precisely ever ellipses for that matter).) So, you have all sorts of orbits. The two most general cases I can think of are 1. In a system of objects which are gravitationally bound and 2. In a system of objects which are close enough to one another such that their paths are significantly influenced by each other's gravity. Finally, and it is (imho) pretty important - the proposed definitions:"In physics, an orbit is the gravitationally curved trajectory of an object." & "In physics, an orbit is the trajectory of an object which is subject primarily to gravitational forces." are both just bad. These both would allow us to describe the path of a bullet, traveling at, say 0.99c relative to the nearest galaxy, and in intergalactic space as "an orbit". That is: neither one adequately distinguishes an orbit from a non-orbit. They both confuse orbit with trajectory. You should consider, imho, WHEN a trajectory will be described as an orbit and stick to those cases, although it is unlikely that you can capture all contexts in a single definition. I suggest that just like dictonaries give multiple definitions of words, that the term here needs several different definitions (in different given contexts).71.31.150.130 (talk) 14:31, 30 January 2018 (UTC)

Orbit = trajectory is unjustified

In the edits of 8 June 2017, Twinsday changed the definition of an orbit from a "path" to a "trajectory". However, the reference for the definition is https://www.britannica.com/science/orbit-astronomy, and that page describes orbit as a "path". NASA defines orbit on its website at https://www.nasa.gov/audience/forstudents/5-8/features/orbit_feature_5-8.html, and there too it is described as a "path". Furthermore, contextual clues suggest that NASA thinks of an orbit as a path. For instance, NASA's orbital elements page at https://spaceflight.nasa.gov/realdata/elements/ uses the phrase "an orbit and a satellite's position within the orbit", which makes sense if an orbit is a path, but not if it is a trajectory. I think this is a case of Wikipedia getting ahead of the literature. I suspect that in practice, "orbit" is ambiguous, with the "trajectory" meaning primary and the "path" meaning secondary. However, the literature does not reflect current practice and unambiguously describes "orbit" as a path. Therefore, I believe Twinsday's edits were premature. Would anyone object if I reverse them? 47.142.130.130 (talk) 16:58, 19 September 2017 (UTC)

The definitions I see for trajectory are clear enough, while path seems unnecessarily less specific. An orbit is a trajectory under gravitational forces. Tom Ruen (talk) 19:35, 6 November 2017 (UTC)

If you see a clear definition of orbit as a trajectory in source material somewhere, then please cite that source material as a reference. As the article stands now, the sentence claiming that an orbit is a trajectory references an article which claims that an orbit is a path. If you are arguing that path and trajectory are substantially the same thing, with path simply being "unnecessarily less specific", then present your argument here so we can hash it out. In the meantime, please revert the article to what the source material supports, rather than using Wikipedia to express your unsupported opinion. — Preceding unsigned comment added by 70.191.93.96 (talk) 23:52, 6 November 2017 (UTC)

Let us start by defining path, it was not linked. - Patrick (talk) 11:46, 7 November 2017 (UTC)

There seems to be a bit of talking over one-another here. A BALLISTIC trajectory often is based on the assumptions that m1→0 (m1 << M2) and that there are no 3rd body influences. Given the widespread use of the term "trajectory" to mean ballistic trajectory within the influence of only one gravitational source and the term "path" to mean the actual ...path...of an object (either in a model system or in the real world), it is obvious that path is better here. Path - in a given coordinate system/frame of reference, the set of positions of an object at given times over a time interval. But everybody understands it. Just stop obfuscating what is perfectly clear. Path - one syllable; trajectory - four syllables and without ANY value here as far as I can see.71.31.150.130 (talk) 14:45, 30 January 2018 (UTC)

I only now have seen your comment, but I had the same issue when I was reading this first time. I added this at the end of the summary, but it was reverted (it was a bit messy I guess):

However because of influence of other bodies (mainly gravitational, but also due to magnetic influences and radiation pressure or Solar and Stellar wind), bodies never being perfectly uniform in density and shape (see for example figure of Earth), or due to loss of mass (best example being comets or rockets), even closely repeating trajectories (commonly referred as orbits), are perturbed and show slow gradual changes in time. Such bodies are still modeled using repeating trajectory parameters, but with orbit parameters (elements) slowly varying over days and years.

It was to some extent to address to general audience a subtle fact that orbits are essentially never a closed trajectories, and are paths. (I am not going to be invoking more complex topics like phase space). 81.6.34.246 (talk) 18:03, 18 October 2018 (UTC)

Awful sections on Relativity and Orbital Planes

So, we either have Newtonian orbits or General Relativistic orbits? Rubbish! Last I heard, Newtonian gravity works instantaneously and simply fails to adequately describe solar system dynamics. Special Relativity (or modified Newtonian Physics with a finite speed of interaction, c) is just as much Relativity as GR is. And then we have the FALSE assertion that orbits are in planes. THEY.ARE.NOT. (except for simple 2-body systems). The Relativity section needs a rewrite and the Orbital Planes section should be removed - its content is false, misleading and trivial.71.31.150.130 (talk) 14:58, 30 January 2018 (UTC)

Link to polar hole explanation

I'd like to link from another article to an explanation of why many earth-observing satellites have "polar holes", areas near the poles where they cannot gather data (obviously not the ones in polar orbits). Can anyone point me to a good explanation of this, preferably in a Wikpedia article? HLHJ (talk) 04:30, 25 February 2020 (UTC)

Merger proposal 7 April 2020

Orbital shell (spaceflight) → Orbit – The article Orbital shell (spaceflight) fails WP:GNG to have its own standalone article. I think that the content in that article can easily be explained in the context of Orbit, and the "Orbit" article is of a reasonable size that the merging of "Orbital shell (spaceflight)" will not cause any problems as far as article size is concerned. --Soumyabrata ^{stay at home} _{wash your hands} ^{to protect from coronavirus} 12:33, 7 April 2020 (UTC)

The Orbit article wouldn't be the right destination. If you're going to merge it, it should be to Satellite constellation, or possibly just transwikified to Wiktionary, with the article reduced to a redirect. Mathglot (talk) 19:04, 11 April 2020 (UTC)

Closing this proposal, given the uncontested objection. To discussed the new proposed target, see Talk:Satellite constellation#Merge proposal. Klbrain (talk) 17:12, 9 November 2020 (UTC)

Dubious

I've tagged "The paths of all the star's satellites are elliptical orbits about that barycenter" becaues I think that's a bad approximation of what really happens with respect to the Earth's orbit. Since our orbit is much closer to the Sun that Jupiter is, it would be more accurate to just say the Earth orbits the Sun, rather than the barycenter of the solar system. See the first answer to [1], which seems like the correct explanation.  — Amakuru (talk) 21:04, 13 September 2020 (UTC)

It may be a bad approximation (I don’t think so), but either way it’s still correct to say that earth orbits the barycenter. Healpa12 (talk) 01:05, 12 March 2021 (UTC)

Mistake in some use of the hat notation?

I've been away from physics for a while so forgive me if I'm completely wrong on this, do let me know, but in the Newtonian analysis of orbital motion section I'm seeing a repeated use of Ô that was confusing me and I realised it's because the article is using this notation for what's quite obviously a non-normalised vector. The hat notation is to represent unit vectors, no? Is this a mistake or am I just misunderstanding something here? CallumMScott (talk) 14:59, 3 September 2024 (UTC)

I agree. Looks like the hat notation is used for unit vectors. Probably ${\hat {\mathbf {O} }}$ should be $\mathbf {O}$ . Let's see if there are any other comments before changing it. Constant314 (talk) 17:31, 3 September 2024 (UTC)