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I've been studying the idea of travelling through space and navigation - in particular: Apollo sextant (used by astronauts to plot the position of their spacecraft relative to stars). And, in order to appreciate the fundamental characteristic of the solar system, in terms of planes and orbits, I've also been reading about the route of the recently discovered interstellar Comet 2I/Borisov, which passed through the ecliptic plane from above and exited below the solar system.

The goal is to visualise how planes (planets) might appear from different parts of the solar system (in terms of Line Of Sight) - parallel to the ecliptic plane and from different compass points... I find the eyes.nasa.gov/apps/ website for Mars really useful for moving through and around the solar system.

Finally, considering that the Moon has a 5° tilt to the Earth, and Mars is on the same ecliptic plane as Earth - where exactly was Mars and Earth and the Moon when this photo was taken by Curiosity Rover as detailed on this space.com article?

I guess Mars was positioned near Earth September Equinox, and Earth positioned just after the Perihelion, and full Moon.

I can't quite understand how the moon seems to be much lower than Earth.

EDIT: answering the general position of the Earth and Moon, which is the first step towards determining the exact.

Interestingly, the light seen from Mars is that reflecting from the surface of the Pacific ocean.

On the question of "exact", there is a difference, obviously, between knowing the exact and general position. And the first knowing is most suited for the purposes of science, navigation, research - whereas the second form of knowing (generally) for the sake of natural curiosity. But, I think there is a great deal to be gained from appreciating both the exact and general position (us and the Earth) in space - I think this can broaden our perspective.

This is (in general) the position of the Earth and Moon as seen from Mars...

Firstly, the mountain range in the background is the same as the range visible in the 2nd image below. We can compare and notice the same peak and shape of the summits.

Curiosity at Dingo Gap

Image of Earth taken by Curiosity Rover

The Dingo Gap is situated at Gale Crater.

Mars, Earth, Moon, in space...

In general... January 31, 2014 - 10:30pm. This broad view looking downwards at the plane.

Solar system illustration

And again...

Solar system illustration

And from beneath the plane... showing us just how far ahead Mars was relative to Earth.

Solar system illustration

Finally, considering the exact position of the Moon in order to answer the question for why the Moon appears to be positioned beneath Earth.

In fact, the Moon, at the time, was midway through its 5° tilt orbit around Earth. And, from certain angles and from such distance from Mars, could have appeared beneath Earth, as shown in the photo taken by Curiosity.

Solar system illustration

Because our galaxy is at an angle, it is difficult to determine where planets are relative to one another - consequently, from one perspective, as shown in the above image, Earth appears to be ahead of Mars. The only absolute way to determine the general position (visually) of planets is from beneath or above the ecliptic plane(?).

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    $\begingroup$ You may find info here at NASA/JPL Horizons ephemeris; ssd.jpl.nasa.gov/horizons.cgi $\endgroup$ – Adrian Howard Jan 21 at 0:49
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    $\begingroup$ BTW, although the inclination of Mars's orbit to the ecliptic plane is quite small (1.851°), given its orbital radius, it can get quite a distance above or below the ecliptic. (Maybe around 7 million km at perihelion). $\endgroup$ – PM 2Ring Jan 21 at 1:29
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    $\begingroup$ Space.com says it was taken on January 31, 2014, “80 minutes after local sunset,” but let’s use 0 h UT—it doesn’t matter much: Mars moves by about ~0.5°/d and the Earth ~1°. The Moon travels about 13.2° per day, but we’ll use an approximation since we don’t know the exact time, although you could find it from Curiosity’s position on Mars. Using JPL Horizon as suggested by Adrian Howard, we have Earth long = 100.8825, lat = -0.0002; Moon long = 101.0055, lat = +0.0136; and Mars long = 359.7556, lat = -1.4133. This should get you going. ;-) $\endgroup$ – Pierre Paquette Jan 21 at 3:39
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    $\begingroup$ There are a lot of resources in the answer to Where can I find the positions of the planets, stars, moons, artificial satellites, etc. and visualize them? you may find that some of them are easy enough to do your self, and in that case you are always welcome to post an answer to your own question. What form do you want your positions in? There's an Ecliptic coordinate system where you can have X, Y, Z in kilometers (or meters or AU or whatever) $\endgroup$ – uhoh Jan 21 at 12:35
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    $\begingroup$ link $\endgroup$ – PM 2Ring Jan 21 at 19:20
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NASA Photojournal item PIA17936 says:

Researchers used the left eye camera of Curiosity's Mast Camera (Mastcam) to capture this scene about 80 minutes after sunset on the 529th Martian day, or sol, of the rover's work on Mars (Jan. 31, 2014).

Between sols 528 and 532, Where is Curiosity? shows it in a place called Dingo Gap at Martian longitude 137.41°, latitude -4.63°.

At that location on Mars in Stellarium, sunset on 2014-01-31 occurs around 21:00 UT, so the picture was taken around 22:20 UT.

JPL HORIZONS gives these J2000 heliocentric positions at that time:

lon. (l) lat. (b) dist. (r)
Mars 168.784° 1.613° 1.662 au
Earth 131.767° -0.001° 0.985 au
Moon 131.732° 0.010° 0.983 au

and these Mars-centric positions:

lon. (λ) lat. (β) dist. (Δ)
Earth 22.935° -2.535° 1.058 au
Moon 22.826° -2.522° 1.059 au

In other words, the Moon should appear about 0.11° west of Earth in the Martian sky, or to the right if Mars's north celestial pole is up:

Stellarium: Earth and Moon from Mars, equatorial orientation

But looking toward the western horizon (zenith up) from a tropical latitude, celestial north is to the right, so the Moon appears below Earth in the photo.

Stellarium: Earth and Moon from Mars, alt-az orientation

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  • $\begingroup$ Beautiful answer! There is certainly something to be said for using real programs that run with easy-to-use GUIs and generate spectacular images instead of downloading tables of state vectors in barycentric coordinates from Horizons and trying to make plots with Python. $\endgroup$ – uhoh Jan 21 at 23:51
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    $\begingroup$ @uhoh Under the hood it's all the same. If you have such a WIP I look forward to seeing it. $\endgroup$ – Mike G Jan 22 at 0:23
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    $\begingroup$ Many+ thanks Mike... I was just checking the Stellarium website. Personally, I think there's great benefit to using the data+programming approach, alongside GUI software. The 'Where is Curiosity': wow! I'll look through all of this info, and aim to draw it out using the elliptical layout to illustrate. $\endgroup$ – Dylan Jan 22 at 0:25
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    $\begingroup$ @Dylan I hope you'll post your illustration as an answer. $\endgroup$ – Mike G Jan 22 at 0:35
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    $\begingroup$ @MikeG - I must admit, I was under the impression that your heliocentric positions table states where each were, what I'd try to do next is (understand them) plot it out on paper. If I can add this to the question later, definitely. $\endgroup$ – Dylan Jan 22 at 0:43

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