Talk:Retrograde and prograde motion

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Missing information[edit]

To make this article comprehensive there are still some more things to include:

  • info about differences between prograde and retrograde orbits in general relativity.
  • info on the orbits and rotations of stars in binary and multiple star systems (talk) 08:57, 19 October 2009 (UTC)


How come this page says there are 8 planets? What about Pluto? (talk) 18:12, 4 September 2011 (UTC)

You didn't get the memo? —Tamfang (talk) 19:41, 10 October 2011 (UTC)

hahaha Pluto is out... ____Ἑλλαιβάριος Ellaivarios____ 01:18, 26 February 2012 (UTC)

the range of inclination[edit]

Recent changes:

... An object with an inclination between -90 and +90 degrees is orbiting or revolving in the same direction as the primary is rotating. ... An object with an inclination between 90 degrees and 270 degrees is in a retrograde orbit.
... An object with an axial tilt between 90 degrees and 270 degrees is rotating in the opposite direction to its orbital direction.

Inclination is the angle between two vectors in 3-space; it is not signed, nor can it exceed 180°.

Am I mistaken? Can someone illustrate for me the difference between negative and positive inclination, or between 120° tilt and 240° tilt? —Tamfang (talk) 19:32, 23 October 2011 (UTC)

There are multiple mathematically equivalent descriptions of the same situation. An inclination <0° is the same as a declination >0° with the line of nodes rotated 180°. An inclination >90° is the same as an inclination <90° with the period negated. Retrograde motion can be described as motion with an inclination >90° with a period >0, or as motion with an inclination <90° with a period <0. It doesn't matter. When solving different problems, different descriptions of the same situation may be more practical. PiusImpavidus (talk) 17:03, 17 December 2015 (UTC)

Still not clear on WHY/HOW retrogate planetary motion occurs[edit]

it seems MOST celestial bodies will follow a prograde motion, but I am not sure the article clearly answers or provides a clear explanation as to why/how retrograde rotation and retrograde orbit occur as well as whether there is any connection between retrograde orbit and retrograde rotation. Don't forget it has to be written in a away that even the amateur or idiot (that's me) should understand it.

____Ἑλλαιβάριος Ellaivarios____ 01:21, 26 February 2012 (UTC)

There are various possibilities. Simulations have shown that is is somewhat "easier" for an object to be captured into a retrograde orbit around a planet than a prograde one. Capture normally requires an interaction with a third body, usually the Sun, or occasionally a pre-existing satellite. It's easier for a body to be captured in the opposite direction than the planet's motion around the Sun or the satellite's motion around the planet. So captured satellites tend to be in retrograde orbits.
Another possibility involves impacts. A planet may have satellites revolving in the same direction as the planet's rotation, but then a collision may reverse the direction of the rotation, leaving the satellites in retrograde orbits. The planet's rotation also becomes retrograde.
Long-period comets have orbits that are aligned pretty randomly. When they fall in from the Oort Cloud, then may end up going around the Sun in any direction. So about half of these comets have retrograde orbits.
DOwenWilliams (talk) 18:34, 31 March 2013 (UTC)

Article scope[edit]

The article scope seems to only consider celestial bodies, yet the scope is not so limited by the article title. So I'm a bit surprised their is no mention of retrograde orbits for artificial satellites. One example of this from earlier this month was at the recent NASA workshop on the Global Exploration Roadmap on 10 April 2014, retrograde orbits are mentioned at 8:55 in the video of the workshop.

Is there any particular reason why? What do others think about expanding the article a bit to address retrograde orbits for artificial satellites? N2e (talk) 18:00, 28 April 2014 (UTC)

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