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Thread: Libration of a Tidally Locked Planet

  1. #1 Libration of a Tidally Locked Planet 
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    I was wondering if anyone has any knowledge about 'libration'. I've been thinking about tidally locked planets a lot lately, and know about the habitable zone [terminator], etc.-- the zone of 'twilight-intense' light in a ring around the planet where life could potentially survive. However, I could only find a few facts about libration-- and it appears to be an oscillating motion.
    Do this mean that the habitable zone with oscillate slightly, and both edges of the rings will actually experience day/night cycles, as opposed to my thinking now-- that the habitable zone around the tidally-locked planet is rigid, and there is no day or night cycles?
    If this is the case-- there is an oscillation that causes some day/night cycle on the edges of the ring....
    How much time would this oscillation be? Would it oscillate and create day/night cycles in the zone of 24 hours [an Earth-day], or would the oscillation occur over more of a 'geologic' time scale-- the light/darkness on the edges of the habitable ring would change over many years?
    And if so, how much could this potentially shift the night/light? A few miles? Hundreds of miles?
    Thanks!!!


    Last edited by Janus; November 24th, 2012 at 02:26 PM.
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    Lunar Phases 2013: Hour by hour depiction of the Moon

    You probably noticed that the Moon appears to rock around, too, tipping and tilting over the course of every month. That's called libration, and is due to the Moon's orbit being elliptical, and slightly tilted with respect to the Earth's equator. We see it from a slightly different angle every day, and that's what causes that apparent motion.

    the video on this page above may give you an idea and an explanation


    Sometimes it is better not knowing than having an answer that may be wrong.
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    Quote Originally Posted by MrPiano View Post
    I was wondering if anyone has any knowledge about 'libration'. I've been thinking about tidally locked planets a lot lately, and know about the habitable zone [terminator], etc.-- the zone of 'twilight-intense' light in a ring around the planet where life could potentially survive. However, I could only find a few facts about libration-- and it appears to be an oscillating motion.
    Do this mean that the habitable zone with oscillate slightly, and both edges of the rings will actually experience day/night cycles, as opposed to my thinking now-- that the habitable zone around the tidally-locked planet is rigid, and there is no day or night cycles?
    If this is the case-- there is an oscillation that causes some day/night cycle on the edges of the ring....
    How much time would this oscillation be? Would it oscillate and create day/night cycles in the zone of 24 hours [an Earth-day], or would the oscillation occur over more of a 'geologic' time scale-- the light/darkness on the edges of the habitable ring would change over many years?
    And if so, how much could this potentially shift the night/light? A few miles? Hundreds of miles?
    Thanks!!!

    There are two main types of libration. One is libration of longitude, which is the effect brought up by Chrispen Evan. The other is libration of latitude which is caused the satellite's own axis of rotation being tilted. The Moon shows both, so it appears to both rock back & forth and nod up & down. The period of these librations will equal that of the satellite's own orbit.

    The degree of libration depends on the conditions. With libration of longitude it would depend on the eccentricity of the orbit, and libration of latitude depends on the axial tilt.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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    Quote Originally Posted by MrPiano View Post
    I was wondering if anyone has any knowledge about 'libration'. I've been thinking about tidally locked planets a lot lately, and know about the habitable zone [terminator], etc.-- the zone of 'twilight-intense' light in a ring around the planet where life could potentially survive. However, I could only find a few facts about libration-- and it appears to be an oscillating motion.
    Do this mean that the habitable zone with oscillate slightly, and both edges of the rings will actually experience day/night cycles, as opposed to my thinking now-- that the habitable zone around the tidally-locked planet is rigid, and there is no day or night cycles?
    If this is the case-- there is an oscillation that causes some day/night cycle on the edges of the ring....
    How much time would this oscillation be? Would it oscillate and create day/night cycles in the zone of 24 hours [an Earth-day], or would the oscillation occur over more of a 'geologic' time scale-- the light/darkness on the edges of the habitable ring would change over many years?
    And if so, how much could this potentially shift the night/light? A few miles? Hundreds of miles?
    Thanks!!!
    The machanics of libration seem pretty straight foreward, but I sense you are looking at the possibility of finding life in a very narrow band around a planet which is tidally locked around a star with one side to hot and the other to cold for life. A very interesting topic, that I've also thought about. I do think it would be possible, but then IMO anywhere life can exist, it will sooner or later.
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    Quote Originally Posted by Janus View Post
    Quote Originally Posted by MrPiano View Post
    I was wondering if anyone has any knowledge about 'libration'. I've been thinking about tidally locked planets a lot lately, and know about the habitable zone [terminator], etc.-- the zone of 'twilight-intense' light in a ring around the planet where life could potentially survive. However, I could only find a few facts about libration-- and it appears to be an oscillating motion.
    Do this mean that the habitable zone with oscillate slightly, and both edges of the rings will actually experience day/night cycles, as opposed to my thinking now-- that the habitable zone around the tidally-locked planet is rigid, and there is no day or night cycles?
    If this is the case-- there is an oscillation that causes some day/night cycle on the edges of the ring....
    How much time would this oscillation be? Would it oscillate and create day/night cycles in the zone of 24 hours [an Earth-day], or would the oscillation occur over more of a 'geologic' time scale-- the light/darkness on the edges of the habitable ring would change over many years?
    And if so, how much could this potentially shift the night/light? A few miles? Hundreds of miles?
    Thanks!!!

    There are two main types of libration. One is libration of longitude, which is the effect brought up by Chrispen Evan. The other is libration of latitude which is caused the satellite's own axis of rotation being tilted. The Moon shows both, so it appears to both rock back & forth and nod up & down. The period of these librations will equal that of the satellite's own orbit.

    The degree of libration depends on the conditions. With libration of longitude it would depend on the eccentricity of the orbit, and libration of latitude depends on the axial tilt.

    --So [still a little confused, out of my element...] would the amount of time the oscillation takes depend on the individual planet, i.e. it could be any range depending on the planet's own rotation, tilt, etc.?
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    Moderator Moderator Janus's Avatar
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    Quote Originally Posted by MrPiano View Post
    Quote Originally Posted by Janus View Post
    Quote Originally Posted by MrPiano View Post
    I was wondering if anyone has any knowledge about 'libration'. I've been thinking about tidally locked planets a lot lately, and know about the habitable zone [terminator], etc.-- the zone of 'twilight-intense' light in a ring around the planet where life could potentially survive. However, I could only find a few facts about libration-- and it appears to be an oscillating motion.
    Do this mean that the habitable zone with oscillate slightly, and both edges of the rings will actually experience day/night cycles, as opposed to my thinking now-- that the habitable zone around the tidally-locked planet is rigid, and there is no day or night cycles?
    If this is the case-- there is an oscillation that causes some day/night cycle on the edges of the ring....
    How much time would this oscillation be? Would it oscillate and create day/night cycles in the zone of 24 hours [an Earth-day], or would the oscillation occur over more of a 'geologic' time scale-- the light/darkness on the edges of the habitable ring would change over many years?
    And if so, how much could this potentially shift the night/light? A few miles? Hundreds of miles?
    Thanks!!!

    There are two main types of libration. One is libration of longitude, which is the effect brought up by Chrispen Evan. The other is libration of latitude which is caused the satellite's own axis of rotation being tilted. The Moon shows both, so it appears to both rock back & forth and nod up & down. The period of these librations will equal that of the satellite's own orbit.

    The degree of libration depends on the conditions. With libration of longitude it would depend on the eccentricity of the orbit, and libration of latitude depends on the axial tilt.

    --So [still a little confused, out of my element...] would the amount of time the oscillation takes depend on the individual planet, i.e. it could be any range depending on the planet's own rotation, tilt, etc.?
    The time of the libration will always equal the time it takes for the planet to complete one orbit. Libration is not a physical "oscillation" of the planet; It is an apparent oscillation as seen from the sun which is caused by either axial tilt or the fact that the orbital speed for elliptical orbits varies over the orbit, but the planet's rotational speed doesn't (Even though the orbital and rotational periods of the planet are equal.)
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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