A Question About the Moon

[onesmallstep]

<p>Here's a head scratcher for the astronomers out there in SDC land. </p><p>It's one of those things that intuitively should work, but doesn't. I have noticed this several times throughout my life, and again today when the sun and the approximate 1/2 moon were in the sky together.</p><p>See my diagram below, if you draw an imaginary line connecting the "horns" of the phase of the moon and then another line perpendicular to the first line, this second line should point directly to the sun...But it doesn't, not even close.&nbsp; If you hold a straight edge up approximating this line, it misses the sun by several degrees.&nbsp; I would think it would be close enough to be within the range of "eyeball error", but it is so far off that it is obvious the sun doesn't fall on this line.</p><p>My question is, why not?<img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-undecided.gif" border="0" alt="Undecided" title="Undecided" /></p><p><br /><img src="http://sitelife.space.com/ver1.0/Content/images/store/0/12/d022edf6-0380-4c25-8c16-40b79409ac43.Medium.jpg" alt="" width="251" height="247" /></p> <div class="Discussion_UserSignature"> </div>

 

[MeteorWayne]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Here's a head scratcher for the astronomers out there in SDC land. It's one of those things that intuitively should work, but doesn't. I have noticed this several times throughout my life, and again today when the sun and the approximate 1/2 moon were in the sky together.See my diagram below, if you draw an imaginary line connecting the "horns" of the phase of the moon and then another line perpendicular to the first line, this second line should point directly to the sun...But it doesn't, not even close.&nbsp; If you hold a straight edge up approximating this line, it misses the sun by several degrees.&nbsp; I would think it would be close enough to be within the range of "eyeball error", but it is so far off that it is obvious the sun doesn't fall on this line.My question is, why not? <br />Posted by onesmallstep</DIV><br /><br />Question and comment. What are you using as a reference to the sun direction?</p><p>Second (and I'm not sure) but are looking at the 3D representation, including the viewing angle from a point on erath and the moon being above or below the ecliptic?</p><p>The answer to the question may clear up my comment.</p><p>I often find that when considering events in the vicinity of the earth, 3D reconstructions are required in order to gain a true understanding.</p><p>Wayne</p> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[kg]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Here's a head scratcher for the astronomers out there in SDC land. It's one of those things that intuitively should work, but doesn't. I have noticed this several times throughout my life, and again today when the sun and the approximate 1/2 moon were in the sky together.See my diagram below, if you draw an imaginary line connecting the "horns" of the phase of the moon and then another line perpendicular to the first line, this second line should point directly to the sun...But it doesn't, not even close.&nbsp; If you hold a straight edge up approximating this line, it misses the sun by several degrees.&nbsp; I would think it would be close enough to be within the range of "eyeball error", but it is so far off that it is obvious the sun doesn't fall on this line.My question is, why not? <br />Posted by onesmallstep</DIV><br /><br />Wow, good observation!&nbsp; I think what you have noticed is Lunar Libration which is a result of the eccentricity and inclination&nbsp;in the&nbsp;moons orbit.&nbsp; The moon does appear to wobble about in the sky.</p><p>http://en.wikipedia.org/wiki/Orbit_of_the_Moon#Libration</p><p>&nbsp;http://en.wikipedia.org/wiki/Image:Lunar_libration_with_phase_Oct_2007.gif</p>

 

[MeteorWayne]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Wow, good observation!&nbsp; I think what you have noticed is Lunar Libration which is a result of the eccentricity and inclination&nbsp;in the&nbsp;moons orbit.&nbsp; The moon does appear to wobble about in the sky.http://en.wikipedia.org/wiki/Orbit_of_the_Moon#Librationhttp://en.wikipedia.org/wiki/Image:Lunar_libration_with_phase_Oct_2007.gif <br />Posted by kg</DIV><br /><br />I don't think that's right. Libration referes to the fact that you can see more than half the moon due to the facts you mention.</p><p>&nbsp;</p><p>But AFAIK, the sun&nbsp;has to light up the side of the sun that is faces </p> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[onesmallstep]

<p>I don't think it's an effect of libration, as MW said that has to do with the wobble of the moon. What I am talking about has to do with the lighting from the sun. I made a&nbsp;good observation of this yesterday, 12-6-08. The moon was a little past 1/2 and the sun was just above the horizon. I extended my imaginary line and it did not intersect the sun as you would think it should.&nbsp; </p><p>It is probably an optical illusion caused by the fact that sun is so much farther away than it appears...But still, it is a very simple problem, there is the light source (sun), there is the lighted object (moon), in the sky together and the orientation of the moon's phase does not seem to "fit" the sun's location.</p><p>I will try to make a better diagram in the next couple of days, for now here is another, maybe simpler description of how to construct my imaginary line: Find the midpoint of the moon's terminator, then find the midpoint of the limb opposing the terminator.&nbsp; Connect these two midpoints and extend this line all the way to the sun's location, the sun should fall on this line, but doesn't.&nbsp;&nbsp;&nbsp;&nbsp; </p> <div class="Discussion_UserSignature"> </div>

 

[MeteorWayne]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I don't think it's an effect of libration, as MW said that has to do with the wobble of the moon. What I am talking about has to do with the lighting from the sun. I made good observation of this yesterday, 12-6-08. The moon was a little past 1/2 and the sun was just above the horizon. I extended my imaginary line and it did not intersect the sun as you would think it should.&nbsp; It is probably an optical illusion caused by the fact that sun is so much farther away than it appears...But still, it is a very simple problem, there is the light source (sun), there is the lighted object (moon), in the sky together and the orientation of the moon's phase does not seem to "fit" the sun's location.I will try to make a better diagram in the next couple of days, for now here is another, maybe simpler description of how to construct my imaginary line: Find the midpoint of the moon's terminator, then find the midpoint of the limb opposing the terminator.&nbsp; Connect these two midpoints and extend this line all the way to the sun's location, the sun should fall on this line, but doesn't.&nbsp;&nbsp;&nbsp;&nbsp; <br />Posted by onesmallstep</DIV></p><p>I undertstand your confusion, but the fact is, at the scale of the solar system light travels in straight lines, so it is impossible for the moon not to be lit exactly in the direction of the sun. Are you using your own observations of the sun position? If so, there is a possible source of misinformation in that the position of the sun is subtly refracted by the atmosphere (as is the moon, but since it's higher the refraction would be much smaller.</p><p>I just know that the physics is immutable, so whatever the reason is for your observations, it is not related to the actual position of the sun.</p><p>So you are basing it on your physical observations of the sun? If so, there are geometric problems with that interpretation. I won't bother with the details right now, if you can be clear about what you are using as a reference to the sun (i.e. is it an astronomical program of some kind, or your actual in the sky observation?)</p> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[onesmallstep]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I undertstand your confusion, but the fact is, at the scale of the solar system light travels in straight lines, so it is impossible for the moon not to be lit exactly in the direction of the sun. Are you using your own observations of the sun position? If so, there is a possible source of misinformation in that the position of the sun is subtly refracted by the atmosphere (as is the moon, but since it's higher the refraction would be much smaller.I just know that the physics is immutable, so whatever the reason is for your observations, it is not related to the actual position of the sun.So you are basing it on your physical observations of the sun? If so, there are geometric problems with that interpretation. I won't bother with the details right now, if you can be clear about what you are using as a reference to the sun (i.e. is it an astronomical program of some kind, or your actual in the sky observation?) <br />Posted by MeteorWayne</DIV><br /><br />No, actual eyeballs on the sky observation.&nbsp; If there is a clear sky where you are right now, approx 4:52 pm est, 12-7-08, you can go outside and observe it, if the sun is still above the horizon.</p><p>That is the crux of my question, it does not appear that the sun is in the right&nbsp;location to cause the moon's phase to be oriented the way it is.&nbsp; I know this is impossible, but why does it seem that way?</p><p>&nbsp;</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[nimbus]

Must be the landscape around you that skews your impression. Probably related, if not the same effect, to the way you can easily misjudge position of stars or meteors in the 180 degree field of view of the sky. Out in space there would likely be no such effect. <div class="Discussion_UserSignature"> </div>

 

[onesmallstep]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Must be the landscape around you that skews your impression.&nbsp; <br />Posted by nimbus</DIV><br /><br />Could be, but I don't really think so.&nbsp; I am concentrating on only two objects, the sun and moon, and constructing a straight line between the two...There's no landscape between these two objects, only clear blue&nbsp;sky.</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[MeteorWayne]

Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Could be, but I don't really think so.&nbsp; I am concentrating on only two objects, the sun and moon, and constructing a straight line between the two...There's no landscape between these two objects, only clear blue&nbsp;sky.&nbsp; <br />Posted by onesmallstep</DIV><br /><br />Look, in physics, this is invioable. The light goes from the sun to the moon. If you draw the line from the horns and make a line perpendicular to that, it points toward the source of the light. Anything else is an optical illusion, and there are amny that could apply. But physics clearly shows that if it's not perfectly aligned, it is some kind of illusion! <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[onesmallstep]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Look, in physics, this is invioable. The light goes from the sun to the moon. If you draw the line from the horns and make a line perpendicular to that, it points toward the source of the light. Anything else is an optical illusion, and there are amny that could apply. But physics clearly shows that if it's not perfectly aligned, it is some kind of illusion! <br />Posted by MeteorWayne</DIV><br /><br />Don't start throwing your physics books at me, I betcha I've had more physics classes than you, having a BS in engineering.&nbsp; I know it is some kind of illusion, that is my question.</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[nimbus]

<p>Well.. What else could it be, if not the landscape? I dont think theres any atmospheric phenom. that could warp what you see to cause it.&nbsp; It's the landscape and/or your ground plane (the permanent sense of the plane your feet are on)&nbsp;affecting your perception of the moon-sun vector with respect to the moon terminator.</p><p>Lots and lots of people make mistakes when judging positions in the sky.. I think even MW does it from time to time </p> <div class="Discussion_UserSignature"> </div>

 

[vogon13]

<p>&nbsp;</p><p>If I understand the question correctly, the shortest line between the sun and moon is incorrect for determining the perpendicularity of the illumed tips of the moon.</p><p>&nbsp;</p><p>The correct line is a segment of a circle that bisects earth and sky.</p><p>&nbsp;</p><p>&nbsp;</p> <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>

 

[vogon13]

<p>&nbsp;</p><p>More:</p><p>&nbsp;</p><p>A 'straight line'&nbsp; (like light rays) from sun to moon when projected on to the hemisphere of the sky will appear curved to you.</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p> <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>

 

[schmack]

<br /><br />Don't forget the effect you see when you poke a straight stick into a pool of water. The stick "appears" to be bent. Could making your observationo through the earths atmosphere be having a similar effect on what is observed? <div class="Discussion_UserSignature"> <p><font size="4" color="#ff0000"><font size="2">Assumption is the mother of all stuff ups</font> </font></p><p><font size="4" color="#ff0000">Gimme some Schmack Schmack!</font></p> </div>

 

[vogon13]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Don't forget the effect you see when you poke a straight stick into a pool of water. The stick "appears" to be bent. Could making your observationo through the earths atmosphere be having a similar effect on what is observed? <br /> Posted by schmack</DIV></p><p>&nbsp;</p><p>Recall in grade school learning about 'Great Circles'&nbsp; ??</p><p>&nbsp;</p><p>Same thing, only drawn on the inside of the sphere of the sky instead of on the outside of the sphere of the earth.</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p> <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>

 

[onesmallstep]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;More:&nbsp;A 'straight line'&nbsp; (like light rays) from sun to moon when projected on to the hemisphere of the sky will appear curved to you.&nbsp;&nbsp;&nbsp;&nbsp; <br />Posted by vogon13</DIV><br /><br />Wow, I like that one, Vog...this is something I have not heard before, but makes a good explanation for the effect in question here.&nbsp; But, if this is true wouldn't it skew all sorts of other astronomical observations?&nbsp; It would literally mean that the shortest distance between two points is not a straight line when it comes to ground based astronomical observations...We would live in a sort of fishbowl.</p><p>I may have to take you off ignore for coming up with that<img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-wink.gif" border="0" alt="Wink" title="Wink" /></p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[crazyeddie]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Don't forget the effect you see when you poke a straight stick into a pool of water. The stick "appears" to be bent. Could making your observationo through the earths atmosphere be having a similar effect on what is observed? <br /> Posted by schmack</DIV></p><p>I had the same thought. &nbsp;It sounds like some sort of refractive effect of the atmosphere. &nbsp;After all, at first and last quarter, the sun should be 90 degrees from the position of the sun, if you are looking at the arrangement of these bodies from a perspective high above the solar system. &nbsp;But from the surface of the Earth, you are looking through a relatively dense atmosphere, so refraction might distort the true positions of the respective bodies, especially when one is close to the horizon.</p> <div class="Discussion_UserSignature"> </div>

 

[MeteorWayne]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Posted by onesmallstep</DIV><br /><br />I'm not sure you ever answered my question, which is relevant. What are you using as a refernce for the direction to the sun in your diagrams?</p><p>Edit, sorry, I see you did. I think if you work the problem in 3D is makes sense. The line between the sun and earth is the ecliptic. But the moon is above or below that line at all times except for 2 instants a month. So where the sun is in our sky is not the same angle as thet in the moon's "sky".</p> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[vogon13]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I may have to take you off ignore for coming up with that&nbsp; <br /> Posted by onesmallstep</DIV></p><p>&nbsp;</p><p>I know it is difficult to take me at times, being the smartest, and funniest one here is fraught with perils, both profound and sublime.</p><p>&nbsp;</p><p>&nbsp;</p> <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>

 

[onesmallstep]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;I know it is difficult to take me at times, being the smartest, and funniest one here is fraught with perils, both profound and sublime.&nbsp;&nbsp; <br />Posted by vogon13</DIV><br /><br />Don't forget the most modest.</p><p>Let me understand correctly, when we see the sun, moon, or any object through the veil of Earth's atmosphere the location where we think we see it is not it's true location?&nbsp; Like the spearfisher that must compensate for the refracting effect of water, the object, be it fish, moon, or Halley&rsquo;s comet is not really where we think it is.&nbsp; </p><p>If the spearfisher wants dinner, he usually aims below the apparent target he sees with his eyes.&nbsp; Likewise, if we could shoot an imaginary spear in a perfectly straight line at the moon, we would aim below the image we see in the sky?, (also assuming instantaneous travel time for our imaginary spear.)</p><p>I would also presume that the effect is more pronounced for objects closer to the horizon than objects higher in the sky since we are looking through more air closer to the horizon.&nbsp; I knew there was some amount of refractive effect due to this which I always&nbsp;assumed was minimal, but apparently the actual difference of the two locations, one apparent, and one real can be quite large...as evidenced just from my little backyard observations. </p><p>I observed the effect of my OP question again today, and the "error" of my imaginary line seems to get bigger as the moon&nbsp;gets higher&nbsp;in the sky, the sun gets lower, and the two get farther apart.&nbsp; However, when I attempted to construct your great circle arc, things seemed to line up somewhat better.&nbsp; Of course I am doing all of this with my "calibrated eyeball" so I can not be certain, but I am leaning your way...for now.<img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-cool.gif" border="0" alt="Cool" title="Cool" /></p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[bobw]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'><br /> Posted by onesmallstep</DIV></p><p>I have been wondering if you are remembering that the moon is a sphere when you draw your lines in your mind.&nbsp; In the picture the slimmest crescent or almost full will both have the same "red" arrow.&nbsp; In reality the slim crescent moon will have the sun almost behind it and the almost full moon will have the sun almost behind you.<br /><br />The real direction to the sun is a vector tangent to the sphere of the moon at the terminator.&nbsp; In your pictures, the top one will have the sun to the right but "out of the page" and the bottom one will have the sun to the right but slightly "into the page".</p><p><br /> <img src="http://sitelife.space.com/ver1.0/Content/images/store/4/6/f4f3c753-80d0-407d-a6da-964a6fbed35c.Medium.jpg" alt="" /></p> <div class="Discussion_UserSignature"> </div>

 

[onesmallstep]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I have been wondering if you are remembering that the moon is a sphere when you draw your lines in your mind.&nbsp; In the picture the slimmest crescent or almost full will both have the same "red" arrow.&nbsp; In reality the slim crescent moon will have the sun almost behind it and the almost full moon will have the sun almost behind you.The real direction to the sun is a vector tangent to the sphere of the moon at the terminator.&nbsp; In your pictures, the top one will have the sun to the right but "out of the page" and the bottom one will have the sun to the right but slightly "into the page". <br />Posted by bobw</DIV><br /><br />Thanks, but yes, I know the moon is spherical, otherwise there would be no phases.</p><p>What you say is correct, but think about it...If the source of light is coming from your yellow arrows the phase would be oriented such that the terminator would be perpendicular to your yellow lines.</p><p>In the top picture for example, if the light rays are coming from the direction of the yellow line, then the bottom half would be lit a little more and the top half lit a little less, resulting in the midpoint of the terminator shifting around to about the 10 o'clock position from the 9 o'clock position.&nbsp; Which would basically leave my diagram as is but with the red arrow shifting location to the position of your yellow arrow.</p><p><br /><img src="http://sitelife.space.com/ver1.0/Content/images/store/0/9/20e322f6-fa68-46fb-89c3-2b162b34b2f4.Medium.jpg" alt="" /><br /></p> <div class="Discussion_UserSignature"> </div>

 

[bobw]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'> Posted by onesmallstep</DIV></p><p>I drew in an additional red line to represent the Z dimension.&nbsp; That yellow line isn't "down", its "out".&nbsp; It is still at a right angle to the vertical red line.</p><p><img src="http://sitelife.space.com/ver1.0/Content/images/store/2/14/02f95624-a4ec-4c4a-8ebd-422508ed71ed.Medium.gif" alt="" /><br /> </p> <div class="Discussion_UserSignature"> </div>

 

[onesmallstep]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I drew in an additional red line to represent the Z dimension.&nbsp; That yellow line isn't "down", its "out".&nbsp; It is still at a right angle to the vertical red line. <br />Posted by bobw</DIV><br /><br />I understand that, the amount your yellow lines go "in" and "out" also determines the phase of the moon.&nbsp; My red lines pointing to the sun also go in and out depending on the phase,&nbsp;however this does not change anything concerning the question posed in&nbsp;the OP.</p><p>Maybe this will help, the lower crescent moons are shown larger to illustrate they are closer to the viewer than the smaller gibbous moon images at the top.&nbsp; The lower red lines pointing to the sun are dashed to illustrate that they would be "hidden" behind the moon because they point in.</p><p><br /><img src="http://sitelife.space.com/ver1.0/Content/images/store/8/1/a834fb67-2f0f-4bb6-a171-52f9b7dee058.Medium.jpg" alt="" /></p> <div class="Discussion_UserSignature"> </div>