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    colbtech's Avatar
    colbtech Posts: 748, Reputation: 66
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    #1

    Jun 16, 2011, 02:42 AM
    Eclipse
    After all the hoohah about the eclipse that occurred last night and as the moon is a satellite of the earth. Surely there is an eclipse every day somewhere on the planet?
    jcaron2's Avatar
    jcaron2 Posts: 986, Reputation: 204
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    #2

    Jun 16, 2011, 06:33 AM
    No, definitely not. First, it can only possibly happen when the moon is at its point in orbit where it is directly opposite the earth from the sun. This only occurs once per orbit (called the synodic month - approximately 29.5 days). If the moon rotated around the earth in the same plane as the earth rotates around the sun (picture all three objects lying on a flat surface like a table, tracing out their almost-circular orbits), then there would be an eclipse every month (at every full moon). However, those orbits are NOT in the same plane. The moon's orbit is inclined approximately 5 degrees from that of the earth around the sun (the latter is called the ecliptic plane). Thus, the moon is only in the same plane as the earth and the sun once every ~13.7 days (that's half of a sidereal month - the time it takes the moon to rotate around the earth. It differs from the synodic month because the earth's movement around the sun doesn't matter for the sidereal month). In order for a lunar eclipse to occur, BOTH of those situations have to occur: the moon must be at its furthest point from the sun in its rotation (i.e. the moon must be full), and it must be at the point in its orbit when it is very close to the ecliptic.
    RickJ's Avatar
    RickJ Posts: 7,762, Reputation: 864
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    #3

    Jun 16, 2011, 06:42 AM

    No. It is a rare occurrence.

    The eclipse that was on the 15th was a Lunar Eclipse. It only happens when the sun, earth and moon are lined up (exactly or almost exactly)...

    It's quite rare.

    Check out these two articles that will explain things a bit better than can be explained in a reply here:

    1. Lunar eclipse

    2. June 2011 lunar eclipse
    Ldog69's Avatar
    Ldog69 Posts: 9, Reputation: 1
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    #4

    Jul 2, 2011, 10:29 PM
    Hahahha, even I remember having this doubt, but let me answer you,
    See eclipse is when all the 3 object are in one line...
    When you say an eclipse should occur every day, I believe that you are unaware of the fact that the planes of motion of all three objects are different,

    "the plane of motion"
    This is what prevents us from seeing an eclipse everyday.
    :)
    RanWiz's Avatar
    RanWiz Posts: 18, Reputation: 2
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    #5

    Aug 2, 2011, 07:33 PM
    Ever so slightly different topic: Eclipses on JUPITER...
    Since there are many moons, and since Jupiter is so vast, there is a much wider window of opportunity for a moon to become between the Sun and some part of Jupiter. Therefore on Jupiter there is not only an eclipse most every day, but often SEVERAL occurring simultaneously! NASA has some good photos of this phenomenon.

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