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I am trying to figure out how you would navigate on Venus. On Earth you can use Polaris as a North Star to find north. Would there be a star on the Venus sky which could function as either a north star or south star?

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    $\begingroup$ It seems unlikely that one could see stars from the surface through the perpetual cloud cover. $\endgroup$ – Organic Marble Jul 31 '17 at 22:37
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    $\begingroup$ If you were navigating in the sky, in some sort of plane, say, the stars are the same as on Earth. It takes a change in location much larger than the distance from here to anywhere else in the solar system for the stars in the sky to look different. For instance, as Earth moves around the sun over the course of the year, it changes location much more than Venus does, which orbits well inside the orbit of Earth. $\endgroup$ – kim holder Jul 31 '17 at 22:51
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    $\begingroup$ @kimholder polaris is our "north star" because of the direction that Earth's axis is pointing. So the question is really "which way does Venus' axis point"? and the answer is that Venus' north star would be at RA=18h11m, Dec=67.16 deg (Wikipedia). But with a little bit of knowledge of the stars, one does not need a North star to navigate. Especially if one is smart enough to build an airplane. astronoo.com/en/articles/axial-tilt-planets.html $\endgroup$ – uhoh Jul 31 '17 at 23:26
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    $\begingroup$ @uhoh - right, i wasn't thinking there at all. Though we are imagining different scenarios - flying blind because your navigation is down. $\endgroup$ – kim holder Jul 31 '17 at 23:29
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A pole star for a given planet would be a star that coincidentally just happens to be in the direction that the planet's axis of rotation is pointed. According to Wikipedia, that direction for Venus is RA=18h11m, Dec=67.16 deg.

You can see on the screenshot that the Earth's pole star Polaris is not exactly at the pole position, and if you watched it over centuries or eons you'd see that its always moving around.

An interesting question might be how to do navigation on Venus without a view of the night sky due to the (very) opaque clouds. An antenna large enough to receive radio signals from the Sun, Jupiter, or a variety of bodies outside of the solar system may not be so portable, and the very thick atmosphere would tend to block X-rays and any directional components that might be found in cosmic rays.

However, a robotic solar power plane flying somewhere around 60 - 80 km above the surface where sunlight can recharge its batteries might venture near the darker parts of the terminator to spot some stars and planets for additional location cues (assuming it had an on-board ephemeris). It wouldn't necessarily need a pole star to do this though.


below: Screen shots from a planetarium view at in-the-sky.org, but with a "star" shape added at the approximate position of a hypothetical north or south pole star for Venus.

Edit: But stating which one is which requires some careful definition as was pointed out by @TomSpilker's comment. If you look down at the solar system "from above" and looked at each planet, you'd see that all planets rotate around the Sun in the same direction, counter-clock-wise. The direction of this rotation is called prograde. If you then look at the direction of the rotation of each planet around its own axis you'd see that Venus and Uranus spinning was retrograde. https://en.wikipedia.org/wiki/Retrograde_and_prograde_motion

So if you use the right hand rule to define a North for each planet, Venus' North points to the same hemisphere as Earth's South. So I've left the plots of the locations of Venus' hypothetical pole stars unlabeled.

Definition of rotation       Axial Tilt
     "retrograde"                2.64°
    right-hand-rule            177.36°

enter image description here

enter image description here

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    $\begingroup$ This raises an interesting question -- the precise forum for which it is appropriate I don't know, maybe worldbuilding.se? How would our ability to navigate the earth have developed and evolved if we didn't have a pole star to start with? $\endgroup$ – Tristan Aug 2 '17 at 17:19
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    $\begingroup$ @Tristan Step back from a Eurocentric point of view for a moment and think of how many civilizations close to the equator and below it (such that viewing polaris was impractical or impossible) did just fine without it. $\endgroup$ – uhoh Aug 2 '17 at 17:27
  • $\begingroup$ How many of those developed reliable transoceanic navigation capability? (Not a rhetorical question, I am not familiar with the history) -- Celestial navigation (and all the technology derived therefrom) isn't as necessary when you can stay near land, but in the middle of a featureless expanse, it's quite a different story. $\endgroup$ – Tristan Aug 2 '17 at 17:32
  • $\begingroup$ @Tristan stars are also helpful when walking or riding on animals for long distances. I'm no scholar of this either, so as for where to ask, perhaps History of Science and Math stackexchange then? $\endgroup$ – uhoh Aug 2 '17 at 18:08
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    $\begingroup$ @Tristan Just saw this post. The polynesians were navigating the Pacific ocean, reliably finding tiny islands hundreds to thousands of km apart, long before the European explorers ventured forth. They did it using multiple references, including stars, but none of those stars were Polaris. $\endgroup$ – Tom Spilker Jun 2 '18 at 18:49

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