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    ASTRONOMY experts? Anyone care to explain why the moon takes 24 hours to rotate once?

    Banned
    I know it is basically gravity that is responsible but anyone care to explain in layman's terms why it is exactly the same as Earth?

    So does this also mean that we can observe the dark side of the moon or is it a case that this side only faces Earth when the sun is blocked from its surface by the Earth?

    20 Comments

    Banned

    The moon doesn't rotate on an axis, hence why you only ever see the "face on the moon" and not the dark side. When the moon is in the way of the sun - its still the same "moon face" thats facing.


    /thread

    ]A nice answer here

    Copy of text:
    Why Do We Only See One Side of the Moon?

    You may have heard references made to the "dark side" of the Moon. This popular, although somewhat inaccurate term refers to the fact that only one face of the Moon, the "near side", is visible to us. The dark side or far side is permanently rotated away from our planet.

    Why is this the case? We all know that the Earth rotates on its own axis, so theoretically, the Moon should also do the same, allowing us to get a full picture of the planetoid. Why are we limited to seeing only 50 percent? It turns out that the speed at which the Moon rotates has lead to this particular phenomenon. Millions of years ago, the Moon spun at a much faster pace than it does now. However, the gravitational influence of the Earth has gradually acted upon the Moon to slow its rotation down, in the same way that the much smaller gravitational influence of the Moon acts upon the Earth to create tides. This influence slowed the rotational period of the Moon to match that of its orbit – about 29.5 days – and it is now "locked in" to this period.

    If the Moon didn't spin at all, then eventually it would show its far side to the Earth while moving around our planet in orbit. However, since the rotational period is exactly the same as the orbital period, the same portion of the Moon's sphere is always facing the Earth.

    Another interesting fact is that actually a little bit more than half of the Moon's surface is observable from Earth. Since the Moon's orbit is elliptical, and not circular, the speed of its orbital travel increases and decreases depending on how close it is to our planet. The rotational speed of the Moon is constant however – and this difference between orbital speed and rotational speed means that when the Moon is farthest from the Earth, its orbital speed slows down just enough to allow its rotational speed to overtake it, giving observers a small glimpse of the usually hidden area. The term for this "rocking" motion of the Moon is called libration and it allows for 59 percent of the Moon to be seen in total (over time).

    Finally, the reason that the far side of the Moon is frequently referred to as the "dark side" is because many people mistakenly think that it never sees any light from the sun. This notion results from a misinterpretation of the fact that it is never illuminated so that it can be observed from Earth. In fact, since the Moon is constantly rotating on its own axis, there is no area of the planetoid which is in permanent darkness, and the far side of the Moon is only completely devoid of sunlight during a Full Moon – when the Sun is facing the Moon with the Earth in between.

    nah the moon actually does rotate,i remember summat about it taking same time to rotate as it takes to orbit the earth, so it virtually keeps the same side facing the earth at all times :thumbsup:

    Original Poster Banned

    guv;8046445

    The moon doesn't rotate on an axis, hence why you only ever see the "face … The moon doesn't rotate on an axis, hence why you only ever see the "face on the moon" and not the dark side. When the moon is in the way of the sun - its still the same "moon face" thats facing./thread


    thread :thumbsup:

    but the moon does rotate. I was wrong about 24 hours though. It makes one rotation every time it orbits the earth (27.32 days). So surely all the surface should be visible at some stage.

    http://upload.wikimedia.org/wikipedia/commons/c/c0/Lunar_libration_with_phase2.gif

    Original Poster Banned

    melipona;8046470

    ]A nice answer here


    Thanks & repped. Reading now :-D

    Also freaks me out that the moon's diameter is EXACTLY 400 times smaller than the sun and exactly 400 times the distance from the sun than it is from the earth, hence a full solar eclipse :w00t:

    and yes, I was watching The SOlar System last night but does my head in sometimes (e.g. enough energy is produced from the sun in 1 second to power the USA for a Million Years!)

    Original Poster Banned

    kungfu;8046547


    Is that image fully rotating once though? Seems to be going back and forward slightly

    csiman;8046569

    Is that image fully rotating once though? Seems to be going back and … Is that image fully rotating once though? Seems to be going back and forward slightly



    yeh its a full rotation, it goes slightly wonky as the orbit of the moon is elliptical not circular. wierd how its rotation is exactly the same speed as its orbit like, prob summat to do with the gravity of earth thats locked it like that tho

    Original Poster Banned

    melipona;8046470

    ]A nice answer hereCopy of text:Why Do We Only See One Side of the Moon? … ]A nice answer hereCopy of text:Why Do We Only See One Side of the Moon? You may have heard references made to the "dark side" of the Moon. This popular, although somewhat inaccurate term refers to the fact that only one face of the Moon, the "near side", is visible to us. The dark side or far side is permanently rotated away from our planet. Why is this the case? We all know that the Earth rotates on its own axis, so theoretically, the Moon should also do the same, allowing us to get a full picture of the planetoid. Why are we limited to seeing only 50 percent? It turns out that the speed at which the Moon rotates has lead to this particular phenomenon. Millions of years ago, the Moon spun at a much faster pace than it does now. However, the gravitational influence of the Earth has gradually acted upon the Moon to slow its rotation down, in the same way that the much smaller gravitational influence of the Moon acts upon the Earth to create tides. This influence slowed the rotational period of the Moon to match that of its orbit – about 29.5 days – and it is now "locked in" to this period. If the Moon didn't spin at all, then eventually it would show its far side to the Earth while moving around our planet in orbit. However, since the rotational period is exactly the same as the orbital period, the same portion of the Moon's sphere is always facing the Earth. Another interesting fact is that actually a little bit more than half of the Moon's surface is observable from Earth. Since the Moon's orbit is elliptical, and not circular, the speed of its orbital travel increases and decreases depending on how close it is to our planet. The rotational speed of the Moon is constant however – and this difference between orbital speed and rotational speed means that when the Moon is farthest from the Earth, its orbital speed slows down just enough to allow its rotational speed to overtake it, giving observers a small glimpse of the usually hidden area. The term for this "rocking" motion of the Moon is called libration and it allows for 59 percent of the Moon to be seen in total (over time). Finally, the reason that the far side of the Moon is frequently referred to as the "dark side" is because many people mistakenly think that it never sees any light from the sun. This notion results from a misinterpretation of the fact that it is never illuminated so that it can be observed from Earth. In fact, since the Moon is constantly rotating on its own axis, there is no area of the planetoid which is in permanent darkness, and the far side of the Moon is only completely devoid of sunlight during a Full Moon – when the Sun is facing the Moon with the Earth in between.


    Understand it now. Thanks :thumbsup:

    /thread lol

    Original Poster Banned

    kungfu;8046598

    yeh its a full rotation, it goes slightly wonky as the orbit of the moon … yeh its a full rotation, it goes slightly wonky as the orbit of the moon is elliptical not circular. wierd how its rotation is exactly the same speed as its orbit like, prob summat to do with the gravity of earth thats locked it like that tho


    Thanks kungfu. repped :thumbsup:

    Banned

    kungfu;8046518

    nah the moon actually does rotate,i remember summat about it taking same … nah the moon actually does rotate,i remember summat about it taking same time to rotate as it takes to orbit the earth, so it virtually keeps the same side facing the earth at all times :thumbsup:



    I blame my teachers!

    Could have sworn the reason was no rotation.... and from the explanation, still don't get how a same rotation pattern to the rotation of the Earth would do as suggested..... But I didn't google it (as you can gather!!) :whistling:

    guv;8047203

    I blame my teachers! :pCould have sworn the reason was no rotation.... … I blame my teachers! :pCould have sworn the reason was no rotation.... and from the explanation, still don't get how a same rotation pattern to the rotation of the Earth would do as suggested..... But I didn't google it (as you can gather!!) :whistling:



    lol. it rotates at a certain speed during its orbit that would keep its same face (virtually) pointing towards the earth, im doing it on my desk with an orange as the moon, and a large flange as the earth, but obvo you cant see it


    edit, ive drew a face on the orange and its not working, oh well good job you cant see it

    When nobody is looking....
    Put a chair in the middle of the room and face it, walk around it making sure that you always face the same direction, half way round your back will be facing the chair and when you are where you started then you will be facing it again.

    Now this time, face the chair and walk around it making sure that you always face the chair, notice that you have to turn as you walk to do this.

    Of course that is only part of the story, now you need a friend to sit on the chair and rotate to simulate the earth, but I aint asking anybody for help to do a moonie!

    Original Poster Banned

    kungfu;8047220

    lol. it rotates at a certain speed during its orbit that would keep its … lol. it rotates at a certain speed during its orbit that would keep its same face (virtually) pointing towards the earth, im doing it on my desk with an orange as the moon, and a large flange as the earth, but obvo you cant see it :(edit, ive drew a face on the orange and its not working, oh well good job you cant see it


    LOL - I just did it with a beer bottle and a football.


    too much time.....................

    time for the pub methinks :-D

    Guv,

    just walk sideways around any central point facing that point and you'll see that you have actually done one full revolution about your own axis.

    I know, very sad!

    Brilliant programme nonetheless (the solar system). I always thought the solar system ended around Pluto, not 500 times as much distance again!

    Banned

    kungfu;8047220

    lol. it rotates at a certain speed during its orbit that would keep its … lol. it rotates at a certain speed during its orbit that would keep its same face (virtually) pointing towards the earth, im doing it on my desk with an orange as the moon, and a large flange as the earth, but obvo you cant see it :(edit, ive drew a face on the orange and its not working, oh well good job you cant see it



    LOL... Unbelievable. I just did the same with a satsuma and roll of sellotape!

    melipona;8047338

    When nobody is looking....Put a chair in the middle of the room and face … When nobody is looking....Put a chair in the middle of the room and face it, walk around it making sure that you always face the same direction, half way round your back will be facing the chair and when you are where you started then you will be facing it again.Now this time, face the chair and walk around it making sure that you always face the chair, notice that you have to turn as you walk to do this.Of course that is only part of the story, now you need a friend to sit on the chair and rotate to simulate the earth, but I aint asking anybody for help to do a moonie!



    Yeh, i can see it. One of those real freaky coincidences. I'm fairly sure the same thing occurs on Mercury too?

    Strong influence in this thread! :-D

    Another strange thing is The sun is 400 times bigger than the moon but the sun is 400 times further away so when an eclipse occurs they both look exactly the same size.

    Original Poster Banned

    guv;8047376

    LOL... Unbelievable. I just did the same with a satsuma and roll of … LOL... Unbelievable. I just did the same with a satsuma and roll of sellotape!Yeh, i can see it. One of those real freaky coincidences. I'm fairly sure the same thing occurs on Mercury too?Strong influence in this thread! :-D


    Bizarre!

    how come you managed to quote Melliponas example of walking around a chair? I dont even see that post :w00t:

    THIS IS POST #19 on my thread

    Banned

    csiman;8047434

    Bizarre! how come you managed to quote Melliponas example of walking … Bizarre! how come you managed to quote Melliponas example of walking around a chair? I dont even see that post :w00t:THIS IS POST #19 on my thread



    Perhaps Mellipona is on the dark side!

    Dunno... post is still there!

    melipona;8046470

    ]A nice answer hereCopy of text:Why Do We Only See One Side of the Moon? … ]A nice answer hereCopy of text:Why Do We Only See One Side of the Moon? You may have heard references made to the "dark side" of the Moon. This popular, although somewhat inaccurate term refers to the fact that only one face of the Moon, the "near side", is visible to us. The dark side or far side is permanently rotated away from our planet. Why is this the case? We all know that the Earth rotates on its own axis, so theoretically, the Moon should also do the same, allowing us to get a full picture of the planetoid. Why are we limited to seeing only 50 percent? It turns out that the speed at which the Moon rotates has lead to this particular phenomenon. Millions of years ago, the Moon spun at a much faster pace than it does now. However, the gravitational influence of the Earth has gradually acted upon the Moon to slow its rotation down, in the same way that the much smaller gravitational influence of the Moon acts upon the Earth to create tides. This influence slowed the rotational period of the Moon to match that of its orbit – about 29.5 days – and it is now "locked in" to this period. If the Moon didn't spin at all, then eventually it would show its far side to the Earth while moving around our planet in orbit. However, since the rotational period is exactly the same as the orbital period, the same portion of the Moon's sphere is always facing the Earth. Another interesting fact is that actually a little bit more than half of the Moon's surface is observable from Earth. Since the Moon's orbit is elliptical, and not circular, the speed of its orbital travel increases and decreases depending on how close it is to our planet. The rotational speed of the Moon is constant however – and this difference between orbital speed and rotational speed means that when the Moon is farthest from the Earth, its orbital speed slows down just enough to allow its rotational speed to overtake it, giving observers a small glimpse of the usually hidden area. The term for this "rocking" motion of the Moon is called libration and it allows for 59 percent of the Moon to be seen in total (over time). Finally, the reason that the far side of the Moon is frequently referred to as the "dark side" is because many people mistakenly think that it never sees any light from the sun. This notion results from a misinterpretation of the fact that it is never illuminated so that it can be observed from Earth. In fact, since the Moon is constantly rotating on its own axis, there is no area of the planetoid which is in permanent darkness, and the far side of the Moon is only completely devoid of sunlight during a Full Moon – when the Sun is facing the Moon with the Earth in between.



    kungfu;8046547



    nice read and nice pic to go with it :thumbsup:

    Original Poster Banned

    Artonox;8048213

    nice read and nice pic to go with it :thumbsup:


    Makes a nice change from all the religious / political threads :thumbsup:

    Keeps the trolls out too :-D
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