Talk:Argument of periapsis

message: Figure 1 is intended to show the argument of periapsis (omega).  In the figure, omega is labeled 'argument of perihelion'.  Perhaps it should be relabeled 'argument of periapsis' to agree with the title.
Mike Kestell 03:35, 23 August 2007 (UTC)
replies: text: Perihelion is what the periapsis is called if the orbit is around the Sun. The image is a svg so it would be easy to change it. Bobby D. DS. 00:04, 25 September 2007 (UTC)
thread_title:  Suggest Correction to Figure 1 

message: The page states that for equatorial orbits, the argument of periapsis is assumed to be:
: \omega = \arccos { {e_x} \over { \mathbf{\left |e \right |} }} 
Can this be right? Argument of periapsis can be in range [0, 360) degrees, while the arccos function has the range of [0, 180] degrees. Formula obviously won't work for periapsides in the III and IV quadrant.
Makes more sense if the formula is:
: \omega = \arctan2 ({e_y}, {e_x})
Because its range are all four quadrants. However, I have no reference for this...
The formula would be correct if the longitude of ascending node is defined differently (ie. 180 degrees for quadrant III, IV periapsides), but that's not what the wikipedia page on ascending node states.  —Preceding unsigned comment added by 109.121.79.228 (talk) 16:01, 19 June 2010 (UTC)
replies: text: Why do |n| and |e| appear in the denominator?  If they're unit vectors then |n| and |e| are both 1 and are not needed.  Should they be deleted, or should the requirement that n and e are unit vectors be dropped? Vaughan Pratt (talk) 21:22, 22 December 2013 (UTC)
replies: text: Good point.  Either way would work, but to avoid confusion with other Wikipedia articles, I removed the unit-vector requirement.  --Lasunncty (talk) 06:35, 1 January 2014 (UTC)
thread_title:  Formula for equatorial orbits incorrect? 

message: The diagram shows a perfectly circular orbit with periapsis exactly 90 degrees from the node. This is unfortunate becuase it masks many subtle details.  For example, precession causes radial motion of the node. The diagram also implies that periapsis occurs at the highest point over the ecliptic.  NOrbeck (talk) 10:36, 16 July 2010 (UTC)
replies: text: I'll work on it.  I didn't intentionally design it that way, but I admit it does appear as you say.  I've actually been admiring this image:  Orbital elements.svg.  Would something like that be better?  --Lasunncty (talk) 12:54, 16 July 2010 (UTC)

text: I agree. Also, the periapse should be labeled. Trying to convey 3D concepts in 2D is inherently confusing (like this figure and the cited alternative); I think two side-by-side images showing the orbit in two different planes would be better. Jdeast (talk) 15:41, 21 June 2011 (UTC)

text: The description says "the plane of reference from South to North", but there is no indication of these directions on the diagram.  I found that confusing.  Which way is "north"on the diagram? 2.31.164.79 (talk) 18:10, 17 September 2017 (UTC)
thread_title:  Diagram could be improved 

message: Article says this:
An argument of periapsis of 90° means that the orbiting body will reach periapsis at its northmost distance from the plane of reference.
which is true, given diagram in Fig. 1.
However, if the inclination of the orbit is between 180 and 360 degrees, in that case the article should specify that an argument of periapsis of 90° means that the orbiting body will reach periapsis at its southernmost distance from the plane of reference.
Yes the orbit in the diagram should be a little elliptical so it is clear what periapsis is, not just some radius on a circle.  — Preceding unsigned comment added by 91.201.80.240 (talk) 12:11, 5 April 2012 (UTC)
thread_title:  arg of periapsis 90deg at northmost distance ? 

message: The “apsis” is the point closest to or furthest from the main object. There are two apses: the apoastron and the periastron. Not the periapsis! From MEEUS, Jean, Astronomical Algorithms, Second Edition, 1998, p. 411: “The word ‘periapse’, used by some authors, is incorrect. The word *perihelion* means the point of the orbit that is closest to the Sun (from the Greek *peri* = near + *helios* = Sun). Similarly, *perigee* is the point closest to the Earth (*ge* = Earth). Therefore, ‘periapse’ would really mean the point closest to the apse; but this is ridiculous, because what is meant is the apse itself!”
This article should thus be renamed "Argument of periastron."
CielProfond (talk) 01:04, 24 November 2020 (UTC)
replies: text: Despite the perhaps incorrect etymology, periapsis is the general term used by most astronomers.  Periastron is specific to stars, so would not be suitable for this general article. --Lasunncty (talk) 06:03, 5 December 2020 (UTC)
thread_title:  Argument of periastron, not periapsis