# Talk:Longitude of the periapsis

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## Applicability to exoplanets?

I've asked for some clarification of how the concepts described here apply to exoplanets on the argument of periapsis talk page. AldaronT/C 03:28, 24 July 2009 (UTC)

## Application in general

What is the practical purpose of this variable? It doesnt denote any physical angle that can be visualized or measured with a protractor. It is the linear sum of two angles existing in entirely different planes. It seems entirely abstract and purposeless. At what point in, say, the computations of planetary positions, for example, might this variable even be useful? The Argument of Periapsis and the Longitude of the Ascending Node are useable and practical and reflect real concepts. I guess that I (a novice) just dont see what this is for, how its used, why we need it, so on. It seems to me that at any point when Longitude of periapsis is being used, we are deducting from it one of the two variables it is comprised of in order to arrive at the other. I am left wondering why we ever derived this variable in the first place - was it just to confuse people? 64.134.140.40 (talk) 01:25, 10 June 2011 (UTC)

Most objects in the solar system have relatively small inclinations, so it just gives a rough idea of where the periapsis is in the orbit without having to do any complex calculations. --Lasunncty (talk) 03:18, 12 June 2011 (UTC)
I agree with the above comment - basically it tells you in what direction the perihelion (perigee, etc) point occurs when projected onto the reference plane, which is convenient for, say, publishing or other situations where a two-dimentional diagram is the only option. — Preceding unsigned comment added by 50.10.91.64 (talk) 21:34, 28 November 2013 (UTC)
I think it makes sense for objects which are roughly in the same plane. For example a bunch of objects that are anti-aligned to the hypothesized Planet Nine have a common Argument of Perihelion that is supposed to be 180° away from that of P9's.J mareeswaran (talk) 22:24, 25 October 2016 (UTC)