Cruithne

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cosmicdustbunnie

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Why is Cruithne referred to as a moon, it doesn't orbit Earth does it? Is it just an asteroid? <div class="Discussion_UserSignature"> <p><font size="2" color="#ff0000">*<font color="#ff6600">t</font><font color="#ffcc00">w</font><font color="#00ff00">i</font><font color="#00ffff">n</font><font color="#00ccff">k</font><font color="#993366">l</font><font color="#0000ff">e </font><font color="#800080">t</font><font color="#ff00ff">w</font><font color="#ff0000">i</font><font color="#ff6600">n</font><font color="#ffcc00">k</font><font color="#00ff00">l</font><font color="#00ffff">e</font><font color="#993366">*</font></font></p> </div>
 
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adrenalynn

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Excellent question. *very* detailed answer to follow. It's one of my favorite NEOs. <div class="Discussion_UserSignature"> <p>.</p><p><font size="3">bipartisan</font>  (<span style="color:blue" class="pointer"><span class="pron"><font face="Lucida Sans Unicode" size="2">bī-pär'tĭ-zən, -sən</font></span></span>) [Adj.]  Maintaining the ability to blame republications when your stimulus plan proves to be a devastating failure.</p><p><strong><font color="#ff0000"><font color="#ff0000">IMPE</font><font color="#c0c0c0">ACH</font> <font color="#0000ff"><font color="#c0c0c0">O</font>BAMA</font>!</font></strong></p> </div>
 
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tony873004

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Here's a webpage I made describing the orbit of Cruithne: http://www.orbitsimulator.com/gravity/articles/cruithne.html<br /><br />It's fun to call it "Earth's 2nd Moon", but it really isn't. It's just a play with words. Cruithne does not directly orbit the Earth in a gravitational sense, as the Moon does. If the Sun instantly vanished, Earth and Cruithne would part ways forever. But the Earth and the Moon would remain together.<br /><br />But the Moon and Cruithne do share one orbital characteristic. They are both in a 1:1 mean motion resonance with Earth. Cruithne's orbit is classified as a horeshoe orbit. It was the second of several objects discovered which are co-orbital with Earth. The first discovered was the Moon. This might be the reason for the confusion. There are at least 4 types of co-orbital orbits:<br /><br />1) Horseshoe Orbits (like Cruithne)<br />2) quasi-orbits (like 2002 AA29, see my webpage: http://www.orbitsimulator.com/gravity/articles/2002aa29.html )<br />3) Trojan or tadpole orbits<br />4) Direct orbits (like the Moon)<br /><br />Any object in one of these orbits will orbit the Sun, on average, once for every one time Earth orbits the Sun. Through various mechanisms, Earth's gravity makes sure that such an object never gets more than an orbit ahead of or behind Earth, ensuring that over long periods of time the ratio averages into exactly 1:1. Additionally, there are other asteroids in resonances other than 1:1 with Earth.<br /><br />The first of these 3 types of co-orbitals I mention often jump from one state to another. For example, 2002 AA29 will ultimately leave its quasi-orbit around Earth and enter a horseshoe orbit.<br /><br />Earth recently has an object that could truly be described as a 2nd moon: 6R10DB9 . This object entered Earth orbit, completed a few la
 
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adrenalynn

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That sums it up pretty well, so I won't bother except for follow-on. I have a theory regarding Cruithne and the triplets. But I'm going to hold off on those theories until the simulations are done. <div class="Discussion_UserSignature"> <p>.</p><p><font size="3">bipartisan</font>  (<span style="color:blue" class="pointer"><span class="pron"><font face="Lucida Sans Unicode" size="2">bī-pär'tĭ-zən, -sən</font></span></span>) [Adj.]  Maintaining the ability to blame republications when your stimulus plan proves to be a devastating failure.</p><p><strong><font color="#ff0000"><font color="#ff0000">IMPE</font><font color="#c0c0c0">ACH</font> <font color="#0000ff"><font color="#c0c0c0">O</font>BAMA</font>!</font></strong></p> </div>
 
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tony873004

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"I have a theory regarding Cruithne and the triplets. But I'm going to hold off on those theories until the simulations are done."<br />But now you have me curious <img src="/images/icons/smile.gif" />
 
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vogon13

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Regarding what happens to moon relative to earth if sun disappears, IIRC, earth's pull on moon is only 40% that of sun's pull on moon.<br /><br />If sun disappears (granted it is unlikely God will misplace it), the moons orbit will be <i><b>greatly</b></i> disturbed.<br /><br />Intersting if anyone has done a sim as to just what would happen . . . .<br /><br /><br />{blammo, kablooey, whomp!}<br /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>
 
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tony873004

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The Earth's gravity accelerates the Moon: GM/d^2 = G*5.97e24/384000000^2=0.00270126953125 m/s/s<br /><br />The Sun's gravity accelerates the Moon: G*1.98911e30/150000000000^2=5.89837418666667E-03<br /><br />So the Earth's gravity accelerates the Moon only 46% that of the Sun's gravity.<br /><br />However, the Sun accelerates the Earth as well, by an almost-identical amount. This cancels out most of its dominance. Since the Moon and the Earth are not exactly the same distance from the Sun, there is some difference. This is a gravitational tide, or gravitational gradient through the Earth Moon system. But this gravity gradient is small compared to the Earth's pull. So Earth wins big-time.<br /><br />Two noticable effects from the solar gravity gradient through the Earth Moon system is the Moon's precession of nodes in an 18 year cycle called the Saros cycle, and its precession of perigee in a 9 year cycle. Here's an animation of these cycles: http://www.orbitsimulator.com/gravity/saros.GIF<br /><br />If the Sun instantly vanished, these cycles would disappear. The Moon's orbit would be virtually frozen in its current instantaneous state.<br /><br />
 
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cosmicdustbunnie

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Thanks guys <img src="/images/icons/smile.gif" /><br /><br />Adrenalynn please tell your theory! i'm so intrigued! <div class="Discussion_UserSignature"> <p><font size="2" color="#ff0000">*<font color="#ff6600">t</font><font color="#ffcc00">w</font><font color="#00ff00">i</font><font color="#00ffff">n</font><font color="#00ccff">k</font><font color="#993366">l</font><font color="#0000ff">e </font><font color="#800080">t</font><font color="#ff00ff">w</font><font color="#ff0000">i</font><font color="#ff6600">n</font><font color="#ffcc00">k</font><font color="#00ff00">l</font><font color="#00ffff">e</font><font color="#993366">*</font></font></p> </div>
 
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jmilsom

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Hey. Very interesting thread. Great site Tony! <div class="Discussion_UserSignature"> </div>
 
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vogon13

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Ah, ha.<br /><br />The moon's orbit would be greatly perturbed, but so too, the earth's, and in a highly symmetrical fashion.<br /><br /><br /><br /><br />Crikey, where is the fun in that dull scenario ??<br /><br /><br /><br /><br /><br /><br /><br />Oh, yeah, the sun is gone, we all freeze and DIE.<br /><br /><br /><br />Nevermind.<br /><br /><br /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>
 
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tony873004

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It might be more correct to say the Moon's orbit would be greatly <i>unperturbed</i>, in contrast to its current greatly perturbed orbit.<br /><br />yes, we would all freeze and die <img src="/images/icons/smile.gif" />
 
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