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Seen from Earth, the sun travels on a year-long orbit across the celestial sphere, passing through the twelve zodiac constellations.

As I understand it, this path depends on our orbital plane---if our orbital plane were tilted, the sun's path would pass through different zodiac constellations.

Is that right? If so, does the sun's annual path pass through different constellations on any other planets in our system? I know that most planets lie in approximately the same orbital plane---but what about Mercury, with a 6.3 degree tilt?

Note that this is not a question about whether the stars themselves will look the same; I know that the interplanetary distance is much smaller than the distance to the nearest stars, so the stars will not noticeably shift as you move throughout our solar system. It is a question about whether the sun's path will transit through different constellations when seen from different planets.

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    $\begingroup$ different but related: How will planets behave in the night sky as seen by Mars colonists? $\endgroup$
    – uhoh
    Nov 22 at 13:30
  • $\begingroup$ Does this answer your question? How will planets behave in the night sky as seen by Mars colonists? $\endgroup$ Nov 22 at 13:37
  • $\begingroup$ @uhoh Might even be a duplicate $\endgroup$ Nov 22 at 13:37
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    $\begingroup$ @fasterthanlight I disagree. This can be answered with a boolean yes/no and a short explanation. There's nothing here about the details of prograde-retrograde motion, oppositions, etc. This question is likely to receive a speedy and concise answer if you don't block answers by closing it, whereas the other question requires a substantially more detailed, planet-by-planet answer, which is why it's remained unanswered for so long. $\endgroup$
    – uhoh
    Nov 22 at 13:43
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Even from Earth, the Sun passes through non-zodiac constellations (if you use IAU constellation boundaries) It spends more time in Ophiuchus than in Scorpio, for instance.

From Mercury, the Sun path would deviate from the Ecliptic (which is indeed defined by the plane of the Earth's orbit). The Sun would still pass through Ophiuchus, and it would also pass into Cetus, and just clip the bottom of Auriga. From Mars, the path of the sun would also just edge into Cetus.

The path of the sun from Mercury is different and it passes through 15 constellations, not only the 13 that the sun passes through as seen from Earth.

Of course you don't have to use the IAU constellation boundaries. You can use the astrological signs, but these are not related to the patterns of stars in the sky, except historically. They just divide the whole sky into 30* slices.

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  • $\begingroup$ Thanks! What sources did you use to determine which constellations the sun would pass through as seen from other planets? $\endgroup$
    – user326210
    Nov 23 at 0:50
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    $\begingroup$ Stellarium, I changed location to Mercury. Turned on a constellation grid and stepped day by day $\endgroup$
    – James K
    Nov 23 at 6:41
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The orbital planes of the different planets are all tilted in various random directions with respect to the equatorial plane of the Sun, and thus tilted in varius random directions with respect to each other.

There is a difference in angle between the Sun's equatorial plane and what is called the invariable plane of the Solar System.

The invariable plane of a planetary system, also called Laplace's invariable plane, is the plane passing through its barycenter (center of mass) perpendicular to its angular momentum vector. In the Solar System, about 98% of this effect is contributed by the orbital angular momenta of the four jovian planets (Jupiter, Saturn, Uranus, and Neptune). The invariable plane is within 0.5° of the orbital plane of Jupiter,1 and may be regarded as the weighted average of all planetary orbital and rotational planes.

The article has a table of the orbital planes of the various planets and some other objects in the solar system, listing how much each orbital plane is tilted compared to the ecliptic (the orbital plane of Earth), the Suns equator, and the invariable plane of the solar system.

https://en.wikipedia.org/wiki/Invariable_plane

As seen from planet Earth, the Sun appears to move thorugh the ecliptic plane, the plane of Earth's orbit.

Of the major planets, the orbit of Uranus is tilted the least from the ecliptic plane, by only 0.77 degree, while the orbit of Mercury is tilted the most compared to the ecliptic plane, by 7.01 degrees.

A tilt of 7.01 degrees is not much, and I expect that the Mercurian zodiac is very simular to Earth's zodiac.

On Earth there are 12 constellations of the zodiac. But the ecliptic plane passes through 13 constellations, with Ophiuchus being the ecliptic constellation not included in the astrological zodiac.

So depending on the exact direction of the tilt of Mercury's orbit, the ecliptic planet of Mercury could pass through Ophiuchus much more or much less, perhaps not passing thorugh Ophiuchus at all. There are examples of other ecliptic constellations where the ecliptic passes very close to their official boundries with aother contellations, and where a slight tilt might make the ecliptic plane pass through other constellations.

Thus you need to find out details about the orbit of any particular planet you are interested and find out how to plot the planet's orbital plane against the background of the stars to trace the apparent movements of the Sun in the sky of that planet.

And possibly there is some specialized astronomy or astrology site on the internet which has done that.

And the orbits of planets in other star systems are tilted very randomly with respect to our solar system, and no doubt there are exoplanets with orbital planes at right angles to that of Earth.

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  • $\begingroup$ Thank you for the background info. Do you know how large, approximately, the constellations are? Maybe we can shortcut the answer to my question (Does the sun pass through different constellations) by comparing the angular size of the constellations to the angular difference in orbital tilt. $\endgroup$
    – user326210
    Nov 23 at 0:48
  • $\begingroup$ @Pierre Paqutte I did not discuss axial titling of the rotational axis of planets but tilting of the orbital planes of the planets relative to each others. $\endgroup$ Nov 24 at 20:33
  • $\begingroup$ @M.A.Golding: You are absolutely right. I apologize for misreading. $\endgroup$ Nov 25 at 0:16

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