# How will planets behave in the night sky as seen by Mars colonists?

Certainly among the first colonists on Mars there will be a few people interested in Astronomy enough to enjoy the night sky.

For them, familliar Mars will be missing and there will be a new, unfamiliar planet instead.

Planet by planet, how will their appearance and especially their behavior as seen from Mars differ from the way they behave in the night sky as seen from Earth?

• Companion question in Space Exploration SE: What will shooting stars look like on Mars? – uhoh May 4 '18 at 6:55
• You're only going one planet further out so broadly, Earth would 'behave' like Venus but apart from that, what are you asking about? Their motions across the sky? Phases? If they'd be easier / harder to observe? – user10106 May 4 '18 at 7:36
• @Kozaky I've written over 1,000 SE questions and I've found that in some cases it's best not to over-constrain a question or spell out exactly the form of the answer ahead of time. You are welcome to post your comment as an answer, but if you just give this a day or two I think you'll find that someone will post an excellent and informative answer to the question in its current form. I think this will be a fun question to answer as-is. – uhoh May 4 '18 at 7:56
• Currently I would only think of answering with "They'd 'behave' more-or-less the same as they do from Earth", which reads as a broad answer to a broad question. That's just why I was asking if there was anything more specific. – user10106 May 4 '18 at 8:49
• Martian analemma is odd: apod.nasa.gov/apod/ap030626.html So planets might move a bit different than as seen from earth as well. – Wayfaring Stranger May 4 '18 at 17:19

This should be a relatively simple problem to solve - which is the Academician's way of saying "do it as a homework problem" :-) .

First thing: find some celestial mechanics calculator and determine when each outer and inner planet is visible in Mars' night sky. That gives you timings.

Next thing: compare the distance from each outer planet to Mars vs. Earth. Maybe start with closest and farthest approach as examples. That'll tell you both the angular extent of the planet as well as the relative brightness compared with Terran observations. Don't forget to add a fudge factor for the atmosphere.

In fact, probably the most obvious difference will be that stars no longer twinkle. (yeah I'm ignoring during serious dust storms). You could use a wicked large primary and have no need of adaptive optic corrections.

BTW there are photos of Earth as seen by the Mars rovers (or maybe just the surveying satellites, I forget) so you can get an idea of the color/features available.

• After thinking about userLTK's comment a while I'm beginning to think the question is indeed too broad for this site. One way to fix would be to ask only about Earth's appearance from Mars, as it would contain all of the necessary science and math to address the other planets later. Since you've already posted an answer, I'd like to ask if you would be OK with me making that change? – uhoh May 6 '18 at 2:32
• @uhoh sure, or you could just post a new question on that specific topic. – Carl Witthoft May 7 '18 at 11:21

Celestia may do what you want.

Summary to "Planet by planet, how will their appearance and especially their behavior as seen from Mars differ from the way they behave in the night sky as seen from Earth?"

• Mercury and Venus are very similar. I don't observe retrograde motion in these planets or Earth.
• Earth: wildly different. It seems much farther away and dimmer.
• Mars: wildly different. It seems much closer and brighter.
• Jupiter and other outer planets: very similar. These mostly creep across the field of distant stars near the ecliptic. Periods are closer to a Martian year than a calendar year. If you track (described below) an outer planet, you can observe its retrograde motion. For instance Jupiter turns retrograde in March 2069 and does not turn prograde until October 2069.

To see that for yourself...

In Celestia 2.7, pick your viewpoint. Let's pick the center of Mars, at latitude 0, longitude 0, altitude 0 km.

(menu)Navigation | Go to Object...
Object Name:  Mars
Latitude:  0
Longitude:  0
Distance: 0
km


Now sometimes the texture wrapped on Mars is visible and we don't want that getting in the way, so let's make Mars invisible.

While we're here, let's also pick "Follow" so that Mars will not leave us behind when we speed up time.

Now we need to find the Sun.

Celestial Browser | (tab)Solar System |
(item) Solar System Barycenter |
(subitem) Sol | (context menu) Center


If we speed up time now, we will be at the center of Mars, always pointed in the same direction (relative to the distant stars), so every Martian year, the Sun will roll back through our field of view. We need to track the Sun. Click on the Sun in the starfield, which will highlight it with four red arrowheads. Then type "T" (the capital letter "T"), which will set us to track Sol.

Now let some time pass. Rather a lot of time. Maybe raise the rate to between 1e+06 and 1e+08 -times faster so some of the outer planets will wander in among the inter planets.

(menubar)Time | (button) 10x faster


(repeat as needed).

It can be helpful to have visible coordinate systems. In my screenshots, the "Ecl" (ecliptic line) is shown, using the toggle on the (menubar)Guides.

You may notice that Mercury's orbit doesn't quite fit in the field of view (shown in the lower-right corner, together with out "Track Sol" and "Follow Mars" conditions). You can narrow the field of view by typing comma, ",", and widen it by typing period, ".". A FOV of 70-ish degrees seems to keep the inner planets in view at all times.

The easiest way to track an outer planet seems to be to wait until the one you want passes Sol, click on it to Select it (which takes focus away from the Celestial Browser, which does not happen if you use the Celestial Browser to Select the planet), then "T" to track it. Retrograde motion should be during periods when the distance to the planet is near minimal.

• Thanks for your tutorial! I think this is a work in progress, if you can add a tl;dr at some point specifically addressing "...Planet by planet, how will their appearance and especially their behavior as seen from Mars differ from the way they behave in the night sky as seen from Earth?" that would be great! – uhoh Apr 28 at 22:27
• @uhoh : Some comments added. Not entirely sure what would be a compact characterization of "behaviour". – Eric Towers Apr 28 at 22:44
• Well wouldn't Mercury and Venus remain a lot closer to the Sun? (also see 1, 2) Wouldn't their synodic periods and times between moving form "morning stars" to "evening stars" be substantially different (3, 4, 5)? Would we see a lot more "lunar" occultations of planets? – uhoh Apr 28 at 22:53
• @uhoh : Seems likely. I'm unlikely to measure these things... – Eric Towers Apr 28 at 22:54
• synodic period is gotten from algebra, maximum elongation from trigonometry; these don't need fancy programs and texture wrappers necessarily – uhoh Apr 28 at 23:00