# at what angle does mars rotate? what is its north star? **URL:** \ **Category:** Factual Questions\ **Created:** [September 29, 2003, 6:50pm UTC](https://boards.straightdope.com/t/at-what-angle-does-mars-rotate-what-is-its-north-star/204526 "2003-09-29T18:50:14Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [September 29, 2003, 6:50pm UTC](https://boards.straightdope.com/t/at-what-angle-does-mars-rotate-what-is-its-north-star/204526/1 "2003-09-29T18:50:14Z")
Mars has seasons. This must be because it’s tilted on its axis, as Earth is. We’re tilted some 23 degrees or so. What about Mars? And what’s Mars’ north star? Does their sky resemble ours except that it spins around a different star? The sky must be virtually the same as ours, except for that. Dopers - any help? ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [September 29, 2003, 7:54pm UTC](https://boards.straightdope.com/t/at-what-angle-does-mars-rotate-what-is-its-north-star/204526/2 "2003-09-29T19:54:48Z")
Mar’s axial tilt is currently 25.19° Orbital Period 686.98 days Inclination of orbit to ecliptic 1.85° and I believe the closest bright star to Mars’s north pole would be Deneb, but I might be a bit adrift. * * * SF worldbuilding at [http://www.orionsarm.com/main.html](http://www.orionsarm.com/main.html) ---
**Author:** ![Bytegeist](https://avatars.discourse-cdn.com/v4/letter/b/9dc877/32.png) [@Bytegeist](https://boards.straightdope.com/u/Bytegeist)\ **Post date:** [September 29, 2003, 7:57pm UTC](https://boards.straightdope.com/t/at-what-angle-does-mars-rotate-what-is-its-north-star/204526/3 "2003-09-29T19:57:18Z")
> [@](#): > > Mars has seasons. This must be because it’s tilted on its axis, as Earth is. We’re tilted some 23 degrees or so. What about Mars? From [this site](http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html), we learn that Mars’ axial tilt (a.k.a. obliquity of orbit) is 25.19 degrees. So, very similar to Earth’s. > [@](#): > > And what’s Mars’ north star? Mars’ north celestial pole is at 317.681 degrees in right ascension (or about 21h 10m), and +52.886 degrees in declination — approximately in the direction of Deneb. It has no “bright” north star however. (Then again, Polaris ain’t that bright either.) > [@](#): > > Does their sky resemble ours except that it spins around a different star? The sky must be virtually the same as ours, except for that. Exactly. A Martian’s celestial sphere will be well nigh identical to ours, except for its axis of rotation. The parallax they’d observe for nearby stars would be larger, because of planet’s larger orbit, but that’s not something you could discern with the naked eye. Or not my eyes, anyway. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [September 30, 2003, 5:24am UTC](https://boards.straightdope.com/t/at-what-angle-does-mars-rotate-what-is-its-north-star/204526/4 "2003-09-30T05:24:47Z")
> [@](#): > > \*Originally posted by CC \* > \*\*The sky must be virtually the same as ours, except for that. \*\* Planets and moons appear in different positions too, obviously. I imagine the earth would look quite impressive through a telescope right about now. ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [September 30, 2003, 5:36am UTC](https://boards.straightdope.com/t/at-what-angle-does-mars-rotate-what-is-its-north-star/204526/5 "2003-09-30T05:36:29Z")
Hmmm… Is Earth’s Moon ever a naked-eye object from Mars? If so, that’d be pretty sweet. ---
**Author:** ![MonkeyMensch](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@MonkeyMensch](https://boards.straightdope.com/u/MonkeyMensch)\ **Post date:** [September 30, 2003, 6:15am UTC](https://boards.straightdope.com/t/at-what-angle-does-mars-rotate-what-is-its-north-star/204526/6 "2003-09-30T06:15:39Z")
> [@](#): > > \*Originally posted by Achernar \* > \*\*Hmmm… Is Earth’s Moon ever a naked-eye object from Mars? \*\* My guess would be maybe, but certainly not now. Realize that right now Earth is a “new Earth for any Martians.” That is to say we are in inferior conjunction for those damned bacteria weak weasels. At most the Moon would present about one half of a degree of angular separation from the image of the Earth. That’s about the size of the full moon. It sounds big but it ain’t. (No rebounds on this, please.) When the Earth is at maximum elongation, (or brightest, nearabouts) as viewed from Mars, the Moon would be around 5 minutes (or around 1/6 the size of the moon) from the Earth in the sky. This is when the Earth is at the best viewing for Martian evening/morning star viewing. And don’t I love the evening star over Mount Olympus… The maybe part comes in with Earth in maximum elangation. The Moon would be a relatively faint object awash in the glow of the brilliant evening star that the Earth would present. If you have sharp eyes and clear skies (and doesn’t a near-vacuum give you good viewing) you could pick it out. ---
**Author:** ![Phage](https://avatars.discourse-cdn.com/v4/letter/p/a4c791/32.png) [@Phage](https://boards.straightdope.com/u/Phage)\ **Post date:** [September 30, 2003, 11:20am UTC](https://boards.straightdope.com/t/at-what-angle-does-mars-rotate-what-is-its-north-star/204526/7 "2003-09-30T11:20:53Z")
Out of curiosity, how was the “North” pole of Mars decided? Was a solar North decided on, and from that the planet’s North and South poles? ---
**Author:** ![Earthworm\_Jim](https://avatars.discourse-cdn.com/v4/letter/e/f07891/32.png) [@Earthworm\_Jim](https://boards.straightdope.com/u/Earthworm_Jim)\ **Post date:** [September 30, 2003, 11:27am UTC](https://boards.straightdope.com/t/at-what-angle-does-mars-rotate-what-is-its-north-star/204526/8 "2003-09-30T11:27:55Z")
Also, IIRC, some think Mars tilt varies pretty significantly over time (due, I believe, to lacking a large moon to hold it steady). ---
**Author:** ![Chicago\_Faucet](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chicago_faucet/32/13910_2.png) [@Chicago\_Faucet](https://boards.straightdope.com/u/Chicago_Faucet)\ **Post date:** [September 30, 2003, 11:46am UTC](https://boards.straightdope.com/t/at-what-angle-does-mars-rotate-what-is-its-north-star/204526/9 "2003-09-30T11:46:45Z")
Cool. On Mars I would be only 15 years old. Ahhh, to be 15 again. Sweet. ---
**Author:** ![bryanmcc](https://avatars.discourse-cdn.com/v4/letter/b/eada6e/32.png) [@bryanmcc](https://boards.straightdope.com/u/bryanmcc)\ **Post date:** [September 30, 2003, 11:47am UTC](https://boards.straightdope.com/t/at-what-angle-does-mars-rotate-what-is-its-north-star/204526/10 "2003-09-30T11:47:29Z")
**Phage** - Since it’s only about two degrees different than ours (and it rotates in the same direction), north was set to be in the same direction as for earth. ---
**Author:** ![BobLibDem](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/boblibdem/32/3149_2.png) [@BobLibDem](https://boards.straightdope.com/u/BobLibDem)\ **Post date:** [September 30, 2003, 11:54am UTC](https://boards.straightdope.com/t/at-what-angle-does-mars-rotate-what-is-its-north-star/204526/11 "2003-09-30T11:54:19Z")
I believe that north on other planets was determined by Earth reference. That side of the orbital plane that is north on Earth is also north for the other planets. It works reasonably well except for the sidespinning Uranus. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 30, 2003, 8:39pm UTC](https://boards.straightdope.com/t/at-what-angle-does-mars-rotate-what-is-its-north-star/204526/12 "2003-09-30T20:39:41Z")
There are at least three ways I can think of that you can define “north” for a planet. You could say that it’s the pole matched most closely to Earth’s north pole; you could define “solar north” based on the Earth and use that to define planetary north, or you could define north to be the direction of angular momentum. I’m not sure which convention is most standard, but they all agree for the case of Mars (and most planets, in fact), so it’s easy. Incidentally, Asimov once had a short story which hinged on the fact that Earth’s moon would be easily naked-eye visible from Mars (as easy as Mercury, at any rate). I _think_ that it was called “The Three Lucifers”, but I might be misremembering that. It’s in one of the Black Widowers collections. Incidentally, since Mars and Earth have close to the same inclination, even though they’re in different directions now, we share much the same set of approximate north stars. Right now, we’re pointed at Polaris, but it shifts slowly due to precession to various other points, and Vega, for instance, is sometimes Earth’s north star. Any star which can be an Earthly north star can approximately be a Martian north star, and versa vice.