Does the moon rotate on its own axis?
Discussion
Think about it.
The Moon consistently displays one face to the Earth (hence the term 'Dark side of the Moon), yet the Moon orbits the Earth.
Therefore the Moon MUST rotate about its own axis - one rotation in any 24 hr period (actually its not quite 24 hrs but I'm not getting into the definition of Solar and Sidereal days).
The Moon consistently displays one face to the Earth (hence the term 'Dark side of the Moon), yet the Moon orbits the Earth.
Therefore the Moon MUST rotate about its own axis - one rotation in any 24 hr period (actually its not quite 24 hrs but I'm not getting into the definition of Solar and Sidereal days).
elanfan said:
Am I being a bit thick here -- but if the Moon rotates how come we always see the same side of it. You know the man in the moon!
this is the cool thing - because of tidal forces, the moon gets locked into this freaky thing where it takes the same time to orbit the earth as it does to spin on its own axis - hence we keep seeing the same bit!elanfan said:
Am I being a bit thick here -- but if the Moon rotates how come we always see the same side of it. You know the man in the moon!
curious_about_astronomy said:
Your question is very interesting because the answer is that, no, the Moon is not unique. Almost all moons in the Solar System keep one face pointed toward their planet. (The only exception we know of is Hyperion, a moon of Saturn.) This tells us it's probably not a coincidence, that there is probably a reason for this to happen, a physical process that happens to most moons to slow their rotation.
That process is called tidal friction. You probably know that the Moon's gravity affects the Earth's oceans. Well, the Earth's gravity also affects the Moon. It distorts the Moon's shape slightly, squashing it out so that it is elongated along a line that points toward the Earth. We say that the Earth raises "tidal bulges" on the Moon.
The Earth's gravity pulls on the closest tidal bulge, trying to keep it aligned with Earth. As the Moon turns, feeling the Earth's gravity, this creates friction within the Moon, slowing the Moon's rotation down until its rotation matches its orbital period exactly, a state we call tidal synchronization. In this state, the Moon's tidal bulge is always aligned with Earth, which means that the Moon always keeps one face toward Earth.
Other planets raise tides on their moons, too, so almost all the moons in the Solar System are tidally synchronized. There's even one planet that is sychronized to its moon! Charon, Pluto's moon, is so large and so close to Pluto that the planet and moon are both locked into the same rotational rate. The Moon slows the Earth's rotation, too, but at a very slow rate, increasing the length of the day by a couple of milliseconds each century.
http://curious.astro.cornell.edu/question.php?numb...That process is called tidal friction. You probably know that the Moon's gravity affects the Earth's oceans. Well, the Earth's gravity also affects the Moon. It distorts the Moon's shape slightly, squashing it out so that it is elongated along a line that points toward the Earth. We say that the Earth raises "tidal bulges" on the Moon.
The Earth's gravity pulls on the closest tidal bulge, trying to keep it aligned with Earth. As the Moon turns, feeling the Earth's gravity, this creates friction within the Moon, slowing the Moon's rotation down until its rotation matches its orbital period exactly, a state we call tidal synchronization. In this state, the Moon's tidal bulge is always aligned with Earth, which means that the Moon always keeps one face toward Earth.
Other planets raise tides on their moons, too, so almost all the moons in the Solar System are tidally synchronized. There's even one planet that is sychronized to its moon! Charon, Pluto's moon, is so large and so close to Pluto that the planet and moon are both locked into the same rotational rate. The Moon slows the Earth's rotation, too, but at a very slow rate, increasing the length of the day by a couple of milliseconds each century.
-
Stuart
Edited by sstein on Tuesday 17th March 20:15
elanfan said:
Am I being a bit thick here -- but if the Moon rotates how come we always see the same side of it. You know the man in the moon!
Captured rotation - the Moon rotates in closely the same time as it takes to orbit the Earth. Due to elements of asymmetry in this situation there are times when you can see more around one limb (edge) and then times when you can see more around the other.ETA much as others have said.
The phenomenon of lunar libration means we can see nearly 60% of the Moon's surface from Earth, but only 50% at any one full moon.
Edited by turbobloke on Tuesday 17th March 20:18
elanfan said:
Am I being a bit thick here -- but if the Moon rotates how come we always see the same side of it. You know the man in the moon!
I agree with you and disagree with everyone else (so far). I think if you could tie a rope to the moon (like a ball on the end of a string) it would not start to wrap around the circumferance of the moon as lunar months passed. Therefore I think the moon is not rotating on its own axis. Fantic SuperT said:
elanfan said:
Am I being a bit thick here -- but if the Moon rotates how come we always see the same side of it. You know the man in the moon!
I agree with you and disagree with everyone else (so far). I think if you could tie a rope to the moon (like a ball on the end of a string) it would not start to wrap around the circumferance of the moon as lunar months passed. Therefore I think the moon is not rotating on its own axis. The Moon's orbital period is 27.322 days
The Moon's axial rotation period is 27.322 days
Ginetta G15 Girl said:
Think about it.
The Moon consistently displays one face to the Earth (hence the term 'Dark side of the Moon), yet the Moon orbits the Earth.
Therefore the Moon MUST rotate about its own axis - one rotation in any 24 hr period (actually its not quite 24 hrs but I'm not getting into the definition of Solar and Sidereal days).
Must not!!The Moon consistently displays one face to the Earth (hence the term 'Dark side of the Moon), yet the Moon orbits the Earth.
Therefore the Moon MUST rotate about its own axis - one rotation in any 24 hr period (actually its not quite 24 hrs but I'm not getting into the definition of Solar and Sidereal days).
Fantic SuperT said:
elanfan said:
Am I being a bit thick here -- but if the Moon rotates how come we always see the same side of it. You know the man in the moon!
I agree with you and disagree with everyone else (so far). I think if you could tie a rope to the moon (like a ball on the end of a string) it would not start to wrap around the circumferance of the moon as lunar months passed. Therefore I think the moon is not rotating on its own axis. place the second ('moon') 6 inches away. take a bite out of the side of this second apple which is furthest away from the first.
Move the 'moon' apple around the 'earth' apple keeping the same side facing the 'earth'.
Notice how it rotates on its axis as it goes round? the bite mark ('alien monitoring base') orientation changes.
mas99 said:
Fantic SuperT said:
elanfan said:
Am I being a bit thick here -- but if the Moon rotates how come we always see the same side of it. You know the man in the moon!
I agree with you and disagree with everyone else (so far). I think if you could tie a rope to the moon (like a ball on the end of a string) it would not start to wrap around the circumferance of the moon as lunar months passed. Therefore I think the moon is not rotating on its own axis. place the second ('moon') 6 inches away. take a bite out of the side of this second apple which is furthest away from the first.
Move the 'moon' apple around the 'earth' apple keeping the same side facing the 'earth'.
Notice how it rotates on its axis as it goes round? the bite mark ('alien monitoring base') orientation changes.
turbobloke said:
UncappedTag said:
How come you always see the same side of the moon if it rotates?
Because if it didn't rotate (in the same period as its orbit) you'd see more than one side 
-
Stuart
Edited by sstein on Tuesday 17th March 20:50
sstein said:
turbobloke said:
UncappedTag said:
How come you always see the same side of the moon if it rotates?
Because if it didn't rotate (in the same period as its orbit) you'd see more than one side :tongue:
-
Stuart
Gassing Station | The Pie & Piston Archive | Top of Page | What's New | My Stuff