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Which moons don't rotate?


Targa
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The Mun, Ike and all of Jool's moons are tidally locked. Gilly and Minmus aren't. A tidally locked moon rotates around itself in the same time it rotates around its planet, this means that it is always showing the same face to its planet. The Moon IRL is tidally locked to the Earth: we only see one side.

While a moon may be tidally locked to its planet, it doesn't mean that it doesn't have a night and day cycle. The "dark side of the Moon" is not always dark, it has a day/night cycle as long as its rotation period (which is the same as its orbital period since it's tidally locked): the "dark" side of the Moon is fully lighted by the Sun during new moons.
It's the same for all the moons in KSP: they have a day/night cycle where each day lasts one rotation period, whether or not they are tidally locked. When standing on a tidally locked moon, the planet it is orbiting will appear not to move at all even if days and nights happen (it would move north and south in the sky if the moon has a non-zero inclination, like Bop and Pol).

For a body to not have any day/night cycle it would need to have a rotation period equal to its orbital period around the Sun, which isn't the case for any planets in KSP.

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???

All moons have day/night cycles. Is this about ones that are tidally locked to their planet (on the wiki, but IIRC Mun, Ike, Laythe, Vall, and Tylo), planets that are tidally locked to Kerbol (none since Moho was spun up in 0.18), or something else?

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4 hours ago, Gaarst said:

(it would move north and south in the sky if the moon has a non-zero inclination, like Bop and Pol).

It will also move east-west by a small amount if the moon's orbit is eccentric.  This is because the moon's orbital angular velocity is variable (faster at perispsis and slower at apoapsis), but its rotational angular velocity is constant.  So for a tidally locked moon in both an inclined* and eccentric orbit, the parent planet in the moon's sky will oscillate in both north-south and east-west directions, resulting in the planet tracing out a small figure 8 pattern.

This also means that even for a tidally locked moon, it's possible to observe more than half its surface from the parent planet.  At times in a moon's orbit, parts along the moon's limb that were previously hidden from view will rotate into view, while parts on the opposite side will rotate out of view.  This is called libration.  From Earth we can, over time, see about 59% of our moon's surface.  Of course we can never see more than 50% at any one time.

(edit)

* Technically it's not the inclination of the orbit that matters, but the inclination of the moon's rotational axis relative to its orbital plane.  In KSP, however, it's one in the same.  All bodies in KSP have axes that are normal to the ecliptic plane.  So if we incline the orbit relative to the ecliptic, we also incline the axis relative to the orbital plane normal by the same amount.
 

Edited by OhioBob
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Also note that even though tidally locked moons do have day-night cycles, the days and nights can last a long time.  Pol, for instance, has an orbital period and day with a duration equal to about 42 Kerbin days.  This means you will have 21 days of sunlight followed by 21 days of darkness.  The long nights is something you have to take into consideration when planning something like a moon base.  Even Mun, with is relatively short period, still has night that lasts nearly 20 hours, compared to only 3 hours on Kerbin.  If you are using solar panels for power, you must be certain to provide enough battery capacity to power the station through the long night.
 

Edited by OhioBob
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On 7/27/2017 at 4:18 PM, OhioBob said:

If you are using solar panels for power, you must be certain to provide enough battery capacity to power the station through the long night.

Or radio-generators.

All moons/bodies rotate, the question is, relative to what? 

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37 minutes ago, Gargamel said:

Or radio-generators.

All moons/bodies rotate, the question is, relative to what? 

Wiki list the Sideral Rotation Period, that is relative to the 'start background'. In any case all have days/nights and some* have looonnnnngggg day/nights.

 

*dozen of kerbin days for Moho, Pol and Bop.

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