Talk:Orbital inclination

retrograde
"An inclination greater than 90° and less than 180° is a retrograde orbit."

Unecessarily confusing. I was searching for what others deem as a retrograde orbit so I could make my computer code as accurate as possible, and found this website. Bad choice to look at it! between 90-180° is a *northbound* trajectory that is retrograde, but there is also *southbound* retrograde orbit that... well, that's why I was searching for this; they have inclinations reported sometimes as 180-270°, but is that how its properly defined by the "space-people"? Maybe -90..-180? I don't know, and neither do you! Which renders your arcticle useless.

I might add, that this distinction is very important during actual rocket launches, otherwise your 12 million dollar payload gets hurled in the completely wrong direction (try it in Kerbal Space Program sometime :P).
 * — Preceding unsigned comment added by 144.138.140.227 (talk) 10:50, 29 December 2019 (UTC)

Picture
Here is a tip for your article: I have just uploaded a neat and simple illustration to Wikimedia Commons that shows just the inclination. See http://commons.wikimedia.org/wiki/Image:Inclination_in_Elliptical_Orbit.png Peo from Danish Wikipedia

I think that the illustration Peo links to is more helpful than the current illustration. The current illustration includes many parameters that are not discussed in this article (and shouldn't be discussed in this article). It might be confusing to someone new to this topic. How do other people feel about changing the image? J. Tyler 21:23, 16 January 2007 (UTC)

Terms and Usage for Inclination, Obliquity, and Axial Tilt
The pages detailing the Planets and the Planetoids (asteroids, TNO, dwarf planets) are great. The authors do great work and I appreciate all the effort and dedication they take. I do have a suggestion, however. I believe that we need some additional consistency regarding some items on the tables. A problem stems from several of the pages using inconsistent relationship reference points for the Inclination, Obliquity, and Ecliptic (earth’s orbital plane) data. In doing so, the pages need to be brought into some consistent term usage. For example:
 * 1) INCLINATION:  The use of the item for INCLINATION, under the Orbital Characteristics table section (under the various Planet/Planetoid pages), is inconsistent.  Suggestion -- INCLINATION should relate to the body's orbital plane in relation to the Earth's ecliptic (orbital) plane.  If the authors use something else, then they need to specify the "from-and-to" relationship.  Otherwise, the reader is open to confusion, assumption, and the need to check alternative source documents.  Examples of variations-of-use that need to be specified on various Planet/Planetoid pages:  Axial Tilt in relation to the Ecliptic, Body's orbital plane in relation to the Sun's equator, Body's equatorial inclination in relation to the Ecliptic).
 * 2) OBLIQUITY:  The use of the items under the Physical Characteristics table section (on the various planet/planetoid pages) is inconsistent, as well.  Some authors use the term:  Axial Tilt.  Others use the term:  Equatorial Inclination.  The ambiguous term, Inclination, is used as well.  Suggestion -- OBLIQUITY should be used, and refer to the Body's equatorial inclination to its own orbital plane around the Host Star.  In the case of satellites and sub-members of binary systems, the relationship can be to the Principal Subsystem Host (instead of the Host Star), but  references to such should be added to the label or to the supporting text.  Im addition, if the author wishes to indicate additional information on the table, that is super -- but doing so should include clarification text
 * Examples: The Pluto page referencing Pluto's axial tilt in relation to its orbital plane and to the Earth's Ecliptic (an unusual relationship reference for a planet’s axial tilt).  Charon's relationship to Pluto (its principal.  Etc.

At present, several of the Planet and Planetoid (asteroid and TNO pages) use INCLINATION and AXIL TILT as table items, without clarification as to the relationships (orbital plane, ecliptic, Sun's equator, etc.). Again, this ambiguity puts the reader in the position of having to go to secondary source documents to verify the intent and accuracy of the page data. I do not know if this is the page best suited to post these suggestions, but I will copy this under the Inclination and Obliquity sections too. Tesseract501 7 March 2007

Calculation
I made a diagram to illustrate the questioned calculation, but I'm not sure it is done well enough for the article, so I put it here for now. -- Theoprakt (talk) 23:46, 8 February 2010 (UTC)

Which angle?
What is Inclination? An angle between the reference plane and the plane of the orbit (as it is stated in the article) or an angle between an orbit and the reference plane at a node (as it is shown on the picture)? These are not equal (if the orbit at the node is not perpendicular to the line of nodes). --Jonah.ru (talk) 11:50, 8 March 2012 (UTC)
 * Took me a moment to realize you were refering to the diagram already in the article. Maybe I should put my little doodle in the article, it does not look half as good as the isometrical view already there, but I think it might help to illustrate the concept of inclination while avoiding the issue you named here. -- Theoprakt (talk) 10:28, 1 April 2013 (UTC)

Planetary Equatorial Alignment
I have a question of which I can't find an answer: How often are the equatorial planes of Venus and Mercury aligned? Is this something which is known? It's needed in a physics competition where an additional non-Newtonian force is assumed between the planets on their plane of rotation. Thank you for you help. — Preceding unsigned comment added by 195.59.118.105 (talk) 09:49, 10 September 2012 (UTC)

±

 * an inclination greater than −90° and less than 90° is a prograde orbit.

What's the difference between negative and positive inclination? —Tamfang (talk) 18:09, 3 July 2013 (UTC)


 * The orientation of the orbit. Inclinations above 180° or below 0° are unnecessary, because such orbits can be characterized using a value of the inclination between 0° and 180° and a different value longitude of the ascending node. --JorisvS (talk) 21:52, 3 July 2013 (UTC)


 * So is there a difference or not? Ideally I'd like to see a diagram showing two orbits, one inclined +n° and another inclined &minus;n°, if the distinction is meaningful. —Tamfang (talk) 01:56, 5 July 2013 (UTC)
 * Orbits with +n° and −n° are tilted in the other direction. However, if you turn of them around 180° in the plane, then these orbits are the same. This is what the longitude of the ascending node does. So, if you have an orbit with parameterized with inclination and longitude (i,Ω)=(−n°,k°), it can also be parameterized with (i,Ω)=(+n°,(k+180)°). The latter is what is done in practice. --JorisvS (talk) 18:52, 25 July 2013 (UTC)

I'd be much happier if the inclination were expressed as an unsigned value, measured at the ascending node. We're talking about the angle between two vectors; when is it ever useful to give that angle a sign? (When they're confined to one plane, that's when.) —Tamfang (talk) 03:39, 26 July 2013 (UTC)
 * Which is what is done anyway: only values between 0° and 180° are used. In principle, one could use higher and lower values, but this is unnecessary. Change it if you like. --JorisvS (talk) 10:11, 30 July 2013 (UTC)

Slight confusion
In the article, it says a zero degree orbit is equatorial, while 180 degrees is retrograde equatorial orbit. I'm almost positive that it means when an object orbits in the opposite direction of a zero degree orbit, but it is not made clear here. Can I get a clarification or a fix to the sentence? (Not that good at astronomy terms, I'm afraid, wouldn't want to screw things up by improper terminology) Leobold111 (talk) 07:01, 20 March 2015 (UTC)
 * An inclination of 180° degrees is the same orbit as 0°, but in the opposite direction, which is what retrograde means. --JorisvS (talk) 09:03, 20 March 2015 (UTC)
 * Told you I'm not good at the terms. Leobold111 (talk) 19:31, 20 March 2015 (UTC)

Apogee drift
Hello! I have added to the Intro to ease in novices, in response to the request via template at the top of the article. I've also rearranged Section 1.1 and fleshed it out. That section includes the terms "apogee drift" and "critical inclination" which are not used elsewhere in Wikipedia, though they are presumably elaborated on in the citation (a .PS file). I'd appreciate it if someone knowledgeable would add detail (maybe a single sentence) in Section 1.1. Spike-from-NH (talk) 01:42, 15 December 2016 (UTC)
 * There should be more info in Orbital perturbation analysis but the article is a clusterfuck. I might give a go at improving it later Spacepine (talk) 02:23, 9 March 2019 (UTC)

About the source of Inclination to Sun's equator data
Recently, trying to convert the orbital parameters of planets I searched for "Orbital inclination" in Wikipedia I found the table with the values of the planet inclinations (in "Observations and theories") calculated with respect to Ecliptic, Sun's equator and Invariable plane. However, references are shown only for the values calculated for the ecliptic and the invariable plane. Naturally one would expect references to the sun's equator as well. This really matters to me and I would be grateful if someone could show the origin (the reference) where to find how these values are calculated. CecoRogo (talk) 09:23, 19 February 2023 (UTC)