# Astronomy: What is it that defines the cardinal directions on extraterrestrial objects?

**URL:** <https://boards.straightdope.com/t/astronomy-what-is-it-that-defines-the-cardinal-directions-on-extraterrestrial-objects/926400>\
**Category:** Factual Questions\
**Created:** [November 25, 2020, 8:34am UTC](https://boards.straightdope.com/t/astronomy-what-is-it-that-defines-the-cardinal-directions-on-extraterrestrial-objects/926400 "2020-11-25T08:34:41Z")\
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**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\
**Post date:** [November 25, 2020, 9:15am UTC](https://boards.straightdope.com/t/astronomy-what-is-it-that-defines-the-cardinal-directions-on-extraterrestrial-objects/926400/3 "2020-11-25T09:15:51Z")

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[Previous thread on the subject](https://boards.straightdope.com/t/how-do-they-decide-which-is-north-and-south-on-an-asteroid/591303).

From the [Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2009](https://astropedia.astrogeology.usgs.gov/alfresco/d/d/workspace/SpacesStore/28fd9e81-1964-44d6-a58b-fbbf61e64e15/WGCCRE2009reprint.pdf):

> **5 Rotational elements for dwarf planets, minor planets, their satellites, and comets**
> 
> For planets and satellites, the IAU definition of north pole is the pole that lies above the invariant plane of the Solar System, and the rotation can be either direct or retrograde.  
> …  
> The choice of a rotational pole for a body in simple rotation with slow precession is straightforward. One can choose the pole that follows either the right-hand rule or the left-hand rule, and the right-hand rule is chosen here. This would be the “positive” pole to avoid confusion with the north-south terminology.

So as **eburacum\_45** notes, for planets and satellites, north is north of the plane of the Solar System. However, dwarf planets, etc. use the right-hand rule, assuming the body isn’t undergoing some complicated, possibly irregular rotation.

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