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Static moon question for a book

  1. Feb 4, 2014 #1
    "Static" moon question for a book

    Hi there,

    I was wondering if some scenario (about the moon) was possible for the book I'm writing (heroic fantasy) :
    - my planet is a standard one, potentially bigger than earth
    - I'd like my moon to be always between my planet and the sun, so whenever it's daytime, you "see" the moon. My guess is that the moon has to orbit on the other way the planet is rotating, at a revolution time around the planet equal to its revolution time around the sun (or almost to compensate the ellipsoid of the orbit + the distance between planet and moon). I don't need precise numbers, only an idea of what it needs.
    So, is it possible ?
    Can I also imagine a moon of pink quartz for instance ? (not a big one) My point is, all the photons from sun going through the moon transforms into a particule that provides magic while you are exposed to. As a consequence, my moon will be invisible except on its disk (every photons going through are no more light, but the ones reverbering on the disk are still photons). Hence the moon is not totally invisible, provides magic always during the day, wherever you live on the planet (I may have an issues at the poles though). I don't care if it takes ages to move on the other side of the planet (the moon can't really be "static" the way I want forever ^^)

    thanks for responding, I appreciate your help :)
  2. jcsd
  3. Feb 4, 2014 #2


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    hi soldierftl! welcome to pf! :smile:
    the sun goes round the earth once a year

    you want the moon to go round the earth once a year?

    then won't it need to be at the same distance as the sun? :wink:
  4. Feb 4, 2014 #3
    Sorry my english is quite bad ^^

    I don't want the moon to go around the earth at all. Actually, it would be like the moon was a planet, going parallel to the earth on a smaller ellipsoid (so the moon will always be between the sun and the earth). But I want my moon not to be millions miles away from earth. I want it to be, like ours, around 345 000km away from earth !

    Do you think this is possible ?
    In the moon referential, earth will be immobile, turning on its axis.
  5. Feb 4, 2014 #4


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  6. Feb 4, 2014 #5
    Ah ! thank you very much, that was exactly what I wanted ^^
    I knew Lagragian points, since I read some things about Theia, but it was not in L1.

    So now I just have to do some calculus with the equations :)

    And what do you think about this moon's visibility ? If it's smaller and farest than our moon, we won't see it at all, not even a circle right ? or we might ?
  7. Feb 4, 2014 #6


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    (btw, it's "farther" or "further" :wink:)

    if it's directly between the Earth and the Sun, there'll be a permanent eclipse

    if it's a little to the side, it'll be visible as a crescent …

    but i don't know how far to the side it can be without eventually drifting away completely
  8. Feb 4, 2014 #7
    Earth, sun & moon are not aligned, so there will never be an eclipse

    why is it a crescent ? because the moon doesnt reflect light to the earth except on its frontier ? (speaking of it as a disk) or due to the earth's shadow (which is not possible ?)

    I was thinking what we would see on the early morning a point growing then a crescent then an ovoid then a crescent on the other side of the ovoid and finally some kind of point/trait : it will be the "contour" of our real moon going from new moon (no contour) to full moon and then new moon again (1 month contour condensated into 1 day on my planet). What's your opinion about it? Do you think this is what would happen ?
    Remember that my moon is totally opaque (incoming light is transformed into "magic particle" at almost 100%, so only the ones reflecting on the sides of the moon are not converted)
  9. Feb 4, 2014 #8


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    i don't really understand what your pink quartz does

    so far as reflected light is concerned, it must be a crescent for the same reason that the real Moon is a crescent when we see it near the sun in daylight
  10. Feb 4, 2014 #9
    this is not real pink quartz. It was an example. The moon will be made of some translucid rock which transforms every photon that goes through into an other particle which is no more "light" but an other particle, a "magitron" for instance ^^ So the moon doesnt reverb any light to the earth, it should be black, but the process doesnt work at 100% and there is diffraction... so this is not a dark hole in the sky neither.
  11. Feb 4, 2014 #10


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    if it's off the Earth-Sun centre line, and doesn't reflect any light towards the earth, then you will never see it, just as we don't when our current moon is close to "new moon" position each lunar month.

    Did you know there are already a satellites at the L1 Lagrangian point ?

    The SOHO satellite was placed at that point for observing the sun. And because of its position between the Earth and the Sun it gave early warning of incoming Coronal Mass Ejections heading towards Earth

  12. Feb 5, 2014 #11
    ah yes, I understand now ^^ In my mind, it would darken the sky where the moon is (like during the night, it would hide stars) but that's false on day !

    So, if my moon reflect light only on its border like I said before, will it be visible ? You know, if only "almost tangential ray of light are reflected to the earth ? Will it be like I explained (a dot growing into almost a circle) ?

    And thanks for SOHO, I didn't know ! that's really interesting, I'll dig up more :D
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