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Is Venus upside down? Does its north point in the same direction as Earth's south? (roughly) Or does it just spin clockwise and its north points towards Earth's north? (also roughly) It seems that the right-hand rule would point Venus north in the same direction Earth's south (roughly) but some have said Venus is not upside down, which I believe would mean Venus' north points (rougly) in the same direction as Earth's north.

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    $\begingroup$ This is probably way overkill for your question, but orientation data for all solar system planets, and many other objects are published by the IAU Working Group on Cartographic Coordinates and Rotational Elements. The publication contains the data as well as an explanation on how they're defined. astropedia.astrogeology.usgs.gov/download/Docs/WGCCRE/… $\endgroup$ Nov 28, 2023 at 15:56
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    $\begingroup$ But doesn't Venus' North point up at some point and then point down as the seasons change, the same way the seasons change on Earth (but unlike Earth, the tilt is closer to 180 degrees on Venus)? $\endgroup$
    – mchid
    Nov 28, 2023 at 15:58
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    $\begingroup$ @mchid, that's not how the seasons change, the poles do not change (much) relative to the distant stars. The poles do point towards and away from the Sun during different seasons, but this is due to the motion of the planet around the Sun, not the poles moving. The diagram on this page may help timeanddate.com/calendar/aboutseasons.html $\endgroup$ Nov 28, 2023 at 16:51
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    $\begingroup$ @GregMiller Okay, I thought it also tilted back and forth but I guess that only happens every 40,000 years and only by a couple of degrees. Thanks for the explanation. $\endgroup$
    – mchid
    Nov 28, 2023 at 17:19
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    $\begingroup$ @mchid, you're not alone, that's what I was taught in school too, along with being able to stand an egg on its end on the equinox. I hope things have improved since then. $\endgroup$ Nov 29, 2023 at 16:35

3 Answers 3

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This is a matter of defintion and convention, not science.

By convention "North pole" is defined to be the pole that lies to north side of the solar system's "invariable plane" (that is the plane in which the planets orbit). And so, by definition, its North Pole points the same way as Earth's North pole (roughly).

However axial tilt is defined relative to the positive pole, as defined by the right-hand-rule. For Earth and five other planets, the positive pole is the North pole. For Venus and Uranus the positive pole is the South pole, so these planets have inclinations that are greater than 90 degrees.

But remember that these are just arbitrary choices of nomenclature.

See this explanation on astronomy.com

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This is a matter of convention and definition, not science (as @jamesk states).

It depends what "north" means. Presumably, you are not asking about magnetic north.

Generally, the celestial north pole is defined relative to a spinning body as the celestial pole in the positive direction along it's axis of rotation, applying the right-hand rule as normal. Celestial poles are the points on the surface of the body intersected by its axis of rotation. This matches your description. Earth and Venus's celestial poles do not align relative to their respective surfaces, and change relative to each other as their relative orbital positions change. Celestial north is used for describing satellites in Earth orbit and is nearly the same as magnetic north, so is usually what "north" means without additional context.

Orbital poles are the surface points of an orbiting object which are intersected by a line through that object's center of gravity and perpendicular to its orbit. The north one is the one in the positive direction when applying the right-hand rule to the object's motion relative to the point it is orbiting (usually a larger object, but it works for two similarly-sized objects as well). This is essentially @jamesk's answer. Because Earth and Venus orbit in essentially the same plane, their orbital poles are essentially parallel. Orbital poles are non-intuitive as applied to a planet, because they sweep through a latitude over the course of about a day. They are much more convenient when discussing relative planetary positions though, and so can also be a natural answer to your question.

Wikipedia has a good summaries: celestial and orbital.

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    $\begingroup$ "Celestial poles are the points on the surface of the body intersected by its axis of rotation." No, celestial poles and orbital poles are on the celestial sphere, as your Wikipedia links explain. Also see astronomy.swin.edu.au/cosmos/c/Celestial+Poles $\endgroup$
    – PM 2Ring
    Nov 29, 2023 at 10:24
  • $\begingroup$ @PM2Ring you are correct. However, the celestial sphere is a separate concept, which didn't seem necessary or helpful here. $\endgroup$
    – fectin
    Nov 30, 2023 at 23:29
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I'm going to disagree with the other two answers in a particular way.

There is a way to take the "roughness" out of this question, and make this question more precise and scientific, not just definition and convention.

Namely, assuming by approximation that one has an inertial coordinate system for the solar system, the axis of each of Venus and Earth can be oriented in such a way that the spin around the axis and the orientation of the axis obey the right hand rule. One can then measure the angle between those two oriented axes. The numerical value of this angle will not depend on which inertial coordinate system you picked.

One could actually do this measurement: put a gyroscope in your spaceship with its axis oriented to have $0^\circ$ angle with the Earth's axis; then fly to Venus and observe the angle between your gyroscope axis and Venus' axis.

To say that Venus is "upside down" with respect to earth would then mean that this angle is $180^\circ$, to within some acceptable error.

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  • $\begingroup$ But this then just gets right back to how to define "upside down." It does not seem obvious that "spinning the other direction" should imply "upside down." So, the answer is still just "It's a matter of convention." $\endgroup$
    – reirab
    Nov 30, 2023 at 23:58

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