View from Earth of an object at EML1

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j05h

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How visible would a large space station be if placed at Earth-Moon L1? These kinds of orbits are generally halos around the Lagrange point, so compared to the full Moon, what degree of the sky would the halo orbit cover? How visible would a 1km, roughly reflective truss be?<br /><br />Thanks,<br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>
 
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vogon13

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IIRC, one (or more?) Lunar Orbiter was photographed from Mt. Wilson, seems like the magnitude was around 13.<br /><br />Doing the math in my head, I am not encouraged, although a much smaller structure if flat on one side could easily produce specular reflections visible to the naked eye, like the Iridium satellites.<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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j05h

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are you saying that even a 1km truss in EML1 would barely appear to the naked eye? <br /><br />josh<br /> <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>
 
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nexium

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Even with the best telescopes, objects on the Moon smaller than about ten meters are esentually invisable from Earth, so that would be about 8 meters, since L1 is only about 20% closer to Earth than the moon. Smaller objects, very brightly lighted would be visable as a point of light. Neil
 
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nimbus

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If I remember the math right, a 1km object at 50km is about 1 degree wide. EML1 is roughly 6000 times further. <div class="Discussion_UserSignature"> </div>
 
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j05h

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Thanks guys! So is it safe to assume that any reasonable space station at EML1 is not going to block the Moon or otherwise really change the view? 6000x further should translate into something only arc-seconds wide, correct? And that means it is visible as basically a point source?<br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>
 
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nimbus

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If my math is correct, and assuming the naked eye can't resolve something smaller than 1', the resolution threshold of a 1km truss would be at a distance of about 3,500km, or very roughly 100 times less than EML1, unfortunately. <br /><br />I'm not sure what sort of telescope you'd need to see it, or if binoculars the average joe can afford could resolve it. <div class="Discussion_UserSignature"> </div>
 
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CalliArcale

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<blockquote><font class="small">In reply to:</font><hr /><p>Thanks guys! So is it safe to assume that any reasonable space station at EML1 is not going to block the Moon or otherwise really change the view? 6000x further should translate into something only arc-seconds wide, correct? And that means it is visible as basically a point source? <p><hr /></p></p></blockquote><br /><br />Bear in mind that the ISS (a lot smaller than 1km, but pretty darned big as spacecraft go) is no more than a point, and it's just a few hundred miles up. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>
 
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j05h

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thanks, Nimbus! The reason I asked the question is there was some opposition based on "spoiling the view" of the Moon if we built a large EML1 transfer station - we're discussing it in M&L. I picked 1km as a large-by-our-standards-but-still-tiny structure for discussion purposes. It's really encouraging to know that it would be something between invisible and a point source.<br /><br />j <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>
 
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nimbus

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Yes, I read that thread.. I'm a novice on almost all aspects of space but I read just about every one of these anticipation and/or number crunching threads. <br /><br />Glad I helped <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>
 
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j05h

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Nimbus - you should contribute to that thread, it can use some fresh ideas.<br /><br /> <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>
 
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nimbus

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I'll try.. I need to learn more, though, lest I suggest ideas too flawed to be useful <img src="/images/icons/smile.gif" /><br /><br />I already do try my best to correct people's understanding of space's proximity and value. <div class="Discussion_UserSignature"> </div>
 
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