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[Paulie pchris00]

With an unexpectedly clear sky last night, I found myself observing the Moon (well before the occultation of Zeta Tauri). I would have guessed the waxing gibbous Moon was about 8 days old at the time. I was caught up in observing and imaging what I could see, not what I might have expected to see.

Later that night, while looking through the images I'd taken, I realized that normally on an eight day old (it was actually nine days old, although I didn't know that yet) Moon, Rupes Recta- the Straight Wall- can be seen. I hadn't noticed it while observing, but I didn't specifically look for it. Later, while looking through my images, I saw that Rupes Recta was in full daylight, and therefore not visible. This led me to believe that libration had turned the visual western limb away from us.

I remembered that in early October 2011 I had noticed libration tilting the other direction, allowing me to see the "far side" along the visual western limb. I checked an image I took October 4 that is a similar lunar phase. Sure enough, the images from these two nights show a starkly different lunar landscape.




October 4, 2011- 7:50 PM CDST.




March 1, 2012- 8:12 PM CST.


Wanting to know more about these two nights, I looked up some information from the Virtual Moon Atlas:


October 4, 2011- 7:50 PM CDST
Distance- 383908km
Apparent Diameter- 31.13’
Lunation- 7.53 days
Illumination- 59.3%
Sub-solar latitude- -1.4°
Libration in latitude- -2° 57’
Libration in longitude- +7° 14’

March 1, 2012- 8:13 PM CST
Distance- 391694km
Apparent Diameter- 30.51’
Lunation- 9.15 days
Illumination- 60%
Sub-solar latitude- 1.5°
Libration in latitude- +1°53 ’
Libration in longitude- -6°0 ’

Credit: Virtual Moon Atlas.


Although the phase looks very similar, VMA gives a difference in lunation of over 36 hours. The difference in illumination, though, is only 0.7%, close enough that even very skilled observers would notice little difference, in my opinion. The difference in libration in longitude, however, is over 13 degrees. Luna's visual western limb was indeed turned away from us last night.


For further comparison, I’ve found an image from October 5, and details from Virtual Moon Atlas.




October 5, 2011- 9:00 PM CDST

Distance- 388667km
Apparent Diameter- 30.74’
Lunation- 8.58 days
Illumination- 69.6%
Sub-solar latitude- -1.4°
Libration in latitude- 4° 09 ’
Libration in longitude- +6° 39’

Credit: Virtual Moon Atlas


While the lunation of 8.58 days on October 5 is still over half a day short of last night's 9.15 days, the Moon shows a much fuller disk, and was over 69% illuminated. It's a neat comparison, but I think October 4 better illustrates the difference in libration.

[Centaur]

That's a fine analysis, Paulie. Thank you; quite interesting. Keep in mind however that librations are not the only effects related to the matter. Correlating the Moon's illumination to its "age" can be misleading. The Moon will gain faster than usual in elongation from the Sun when nearer to perigee than apogee. Hence comparisons from different months of the Moon at a particular age can result in varying fractions of its apparent disk being illuminated.

[Paulie pchris00]

Mar 2, 2012 18:05:44 GMT -6 Centaur said:

That's a fine analysis, Paulie. Thank you; quite interesting. Keep in mind however that librations are not the only effects related to the matter. Correlating the Moon's illumination to its "age" can be misleading. The Moon will gain faster than usual in elongation from the Sun when nearer to perigee than apogee. Hence comparisons from different months of the Moon at a particular age can result in varying fractions of its apparent disk being illuminated.

Thank you. I knew that, but hadn't considered it. It's been a long week, and I can't wrap my brain around all the factors involved at my best, let alone when I'm worn out. I will try to keep it in mind from now on, though.

[Paulie pchris00]

This video has been posted somewhere on another thread, but this one includes some explanations, which might be useful, especially for newer members.

[Centaur]

Sorry, but that “tilting” in the video is mainly due to various perspectives as the Moon appears in different portions of the sky as the Earth rotates, and not libration. And as is so typical of popular science writers, they attribute an effect to ellipticity rather than eccentricity. That leads to the confusion seen in this thread: www.bautforum.com/showthread.php/129115-Orbit-calculation . I’ve seen far better animations that illustrate librations: www.inconstantmoon.com/not_libr_ac.htm . NASA and Phil Plait get a D. You get an A for effort.

[Paulie pchris00]

Mar 5, 2012 17:33:50 GMT -6 Centaur said:

Sorry, but that “tilting” in the video is mainly due to various perspectives as the Moon appears in different portions of the sky as the Earth rotates, and not libration. And as is so typical of popular science writers, they attribute an effect to ellipticity rather than eccentricity. That leads to the confusion seen in this thread: www.bautforum.com/showthread.php/129115-Orbit-calculation . I’ve seen far better animations that illustrate librations: www.inconstantmoon.com/not_libr_ac.htm . NASA and Phil Plait get a D. You get an A for effort.

Phil Plait is telling us "Bad Astronomy?!?" How ironic...

[Paulie pchris00]

I haven't written much for my blog lately, but I happened to check my reader stats Wednesday, and saw that the version of this thread that is posted on my blog had a couple hundred hits this week. I've never had any post get read so much in such a short time span. I looked to see where the traffic was coming from, and found my post linked to on the conspiracy theory site Above Top Secret.

www.abovetopsecret.com/forum/thread868768/pg1

I've responded to it, and linked back here.

I'm kind of upset that one of the few things I've done that was rather scientific- confirming the predicted libration of Virtual Moon Atlas with observation- is being used to support some wild claim (that really isn't stated, but I can read between the lines). Maybe we can edumacate some of the woo-woo here.

[patrickm]

Mar 2, 2012 18:05:44 GMT -6 Centaur said:

The Moon will gain faster than usual in elongation from the Sun when nearer to perigee than apogee. Hence comparisons from different months of the Moon at a particular age can result in varying fractions of its apparent disk being illuminated.

My job here is to ask: what?

[Centaur]

Aug 10, 2012 15:31:23 GMT -6 patrickm said:

Mar 2, 2012 18:05:44 GMT -6 Centaur said:

The Moon will gain faster than usual in elongation from the Sun when nearer to perigee than apogee. Hence comparisons from different months of the Moon at a particular age can result in varying fractions of its apparent disk being illuminated.

My job here is to ask: what?

I suggest that you reread my statement and then think it through. If that fails, then your job here is to present your question with more than simply "what".

[Chicago Astronomer - Astro Joe]

Needs car chases and explosions.

[patrickm]

Thanks for that suggestion, Curt. I read it three times before I posted and I don't understand it. I read it out loud to my wife. She doesn't understand it either.

I don't think I am an idiot, but I am a liberal arts major. My brain clearly works differently than yours and Paulie's. My educational background is different. I'm sure my multiple sclerosis-challenged, slightly above average IQ is much lower than yours as well. So if your goal here is to educate, then occasionally further explanation in layman's terms would likely be helpful. If your goal is otherwise, then I guess don't bother. If this place is for people who understand things at a higher level to have discussions among themselves, and is thus exclusionary, then I'll stop asking what jargon-filled statements mean.

I also try to speak not only for myself but for the many lurkers here who are too shy to speak up.

[Centaur]

Aug 10, 2012 17:05:55 GMT -6 patrickm said:

Thanks for that suggestion, Curt. I read it three times before I posted and I don't understand it. I read it out loud to my wife. She doesn't understand it either.

I don't think I am an idiot, but I am a liberal arts major. My brain clearly works differently than yours and Paulie's. My educational background is different. I'm sure my multiple sclerosis-challenged, slightly above average IQ is much lower than yours as well. So if your goal here is to educate, then occasionally further explanation in layman's terms would likely be helpful. If your goal is otherwise, then I guess don't bother. If this place is for people who understand things at a higher level to have discussions among themselves, and is thus exclusionary, then I'll stop asking what jargon-filled statements mean.

I also try to speak not only for myself but for the many lurkers here who are too shy to speak up.

My statement was a reply to Paulie's initial post of this thread. It was for no other purpose. I presumed he would understand. He responded that he did. That is what mattered. When I am responding to someone who I believe has a certain level of astronomical understanding, I am not going to write a chapter length article for the benefit of the lowest common denominator. However, I'm happy to amplify for those who ask more than "what".

I have no way of knowing your degree of astronomical knowledge or understanding of jargon, if you simply ask "what". Sorry, but I am not a mind reader. Perhaps googling the terms will be sufficient. A community college course in astronomy may be helpful. In any event, if you provide some insights into what you did and did not grasp, I would attempt a clarifying response.

[patrickm]

I would never expect anybody to define every term that they use in every sentence, here or anywhere else. That is clearly absurd and also clearly not what I was requesting or suggesting. I was asking about a specific sentence that I could not get to add up.

[Centaur]

Aug 10, 2012 17:38:30 GMT -6 patrickm said:

I would never expect anybody to define every term that they use in every sentence, here or anywhere else. That is clearly absurd and also clearly not what I was requesting or suggesting. I was asking about a specific sentence that I could not get to add up.

Nothing is “clear” when the question is simply “what”. No mention appears to be forthcoming of what specifically or generally was not understood. Therefore I have no idea if the problem is with a single word or the entire concept. So let’s just drop it.

[Centaur]

Aug 10, 2012 17:03:12 GMT -6 Chicago Astronomer - Astro Joe said:

Needs car chases and explosions.

LOL. Love it. I have a computer word game in which one of the bots indicates frustration by saying he would rather see car chases and things blowing up.

[Centaur]

Aug 10, 2012 17:05:55 GMT -6 patrickm said:

...So if your goal here is to educate, then occasionally further explanation in layman's terms would likely be helpful...

If I had initiated the thread, that would be a quite reasonable suggestion. However, since I was replying to a rather knowledgeable astronomer who had initiated the thread, my goal was to write in succinct language that he would be expected to understand. He did. Nevertheless, I would have been happy to have elaborated for a curious layman, if he had indicated his degree of expertise and described the specific matters that puzzled him with a query more descriptive than "what".

BTW, my college degree is in business management. Astronomy was one of the original liberal arts. I never took a course in the subject. I'm very sorry to learn about your MS. I have a good friend who has it. I hope a cure is soon discovered that would greatly benefit both of you and so many other good people.

[Centaur]

Aug 10, 2012 7:04:59 GMT -6 Paulie pchris00 said:

I haven't written much for my blog lately, but I happened to check my reader stats Wednesday, and saw that the version of this thread that is posted on my blog had a couple hundred hits this week. I've never had any post get read so much in such a short time span. I looked to see where the traffic was coming from, and found my post linked to on the conspiracy theory site Above Top Secret.

www.abovetopsecret.com/forum/thread868768/pg1

I've responded to it, and linked back here.

I'm kind of upset that one of the few things I've done that was rather scientific- confirming the predicted libration of Virtual Moon Atlas with observation- is being used to support some wild claim (that really isn't stated, but I can read between the lines). Maybe we can edumacate some of the woo-woo here.

I checked out that other thread, Paulie. Obviously that forum was specially designed to entice credulous woos who imagine the most incredible things, and seem to believe that all truly knowledgeable people have joined a massive permanent leak-proof conspiracy to hide truths from them. As you note, the complaint in this case is not specifically spelled out. I can only imagine it has something to do with mysterious forces or entities that the thread initiator supposes are able to manipulate the Moon’s movements. As you know, the Moon’s dynamics are quite complicated. Newton said the problem gave him headaches. But he and others eventually developed rational solutions. You’re response was marvelous, but it will fall on substantially deaf ears that only receive what they want to hear.

[RobbW]

Paulie, I just read your reply on the ATS forum. Awesome job laying down the facts and smacking them upside the head with science! Ain't science neat?!?!

[Chicago Astronomer - Astro Joe]

I like Libations.

[Paulie pchris00]

Where to start, where to start?

Joe: libations are good, but don't drive afterward.

Robb: thanks, but as Curt says, it probably won't do much good. I'd like to see a response from the initiator of the thread, but from what I can tell, by the time I found it, interest in that thread had fallen off substantially. Probably a good thing.

Patrick, I doubt I think much differently than you. My brain dislikes working with numbers. I sometimes wish it didn't, but it does. I had the advantage of taking two semesters of introductory astronomy at Purdue University North Central shortly after I got into astronomy. I learned the science side of our hobby in the best possible way, in a structured environment, from knowledgeable instructors. I learned to observe on my own, through reading books, magazines, and online articles, again, the best possible way, in my opinion.

The statement that puzzled you made sense to me. It's not how I would put it, but it made sense to me. I don't know if I can explain it any better, and certainly not in fewer words. I'll try to explain the entire thing, as best I can.

In my mind, a first quarter Moon is seven days old. That's a reasonable assumption, but not always correct. In the two images I compared, the percentage of illumination was within 1%, so the phase according to the percentage of illumination was very comparable.

In the first image, though, the lunation was 7.53 days. In the second image the lunation was 9.15 days. Lunation refers to the time since what Curt calls geocentric conjunction with the Sun (please correct me if I have that wrong), which is what we more commonly call New Moon. It specifically refers to the moment (again, correct me if I'm wrong) that the Sun and Moon share the same celestial longitude from the point of view Earth. An object in orbit speeds up when it is closer to the object it is orbiting (and as pointed out above, the Moon's orbit is eccentric- off-center- and elliptical, so it's distance varies through the cycle), and slows down when farther away. We call the Moon's closest point to Earth perigee, and farthest point from Earth apogee.

Now, back to the difference in lunation. The first image, October 4, the Moon was 383908 Km from Earth. The second image, March 1, the Moon was 391694 Km from Earth, a difference of 7,786 Km, according to Virtual Moon Atlas. Being nearer to Earth on October 4, the Moon was orbiting faster than March 1, and took only 7.53 days after "new" to reach almost 60% illumination. Being farther from Earth on March 1, it had taken the Moon 9.15 days after "new" to reach 60% illumination. Does this make sense?

So, when I see a first quarter Moon, off the top of my head I assume it to be about seven days old. This will always be close, but due to the Moon's variable orbital speed, it's not always the case. Obviously, when thinking it through, I know this. As astronomers we often estimate when explaining things to the public, like stating that Saturn is a billion miles away when we know it's more like 900 million. It's a good figure to keep in the top of your head, but not exactly accurate. I questioned why there was over a day and a half difference in lunation between these two similar phases of the Moon, and Curt pointed out what I should have already considered, but hadn't. His statement made sense to me, I went back and checked the lunar distances between those two nights, and had a "duh" moment. Lunar observing is hard, when trying to make sense of it all, and I'm sure even astrophysicists have their "duh" moments. Nobody is putting you down for not understanding.

Curt, I appreciate your input, but your reply to Patrick seemed a little condescending. Your point was valid, but kind of edgy in tone. I saw Patrick at his store a few days after the original post, and remember discussing libration then. I failed to explain it well at that time. Patrick's "what?" looks like a smart@$$ remark, but I know he truly wanted to understand what we were discussing. Who better to ask here than you?

Now, can we all get along?


Okay, for anybody who still doesn't understand, here are your car chases and explosions.

[patrickm]

Thank you, Paulie. I now understand this perfectly!! I had never thought about it that way.

My college astronomy class was one of my least favorite classes in four years of school. I got an A, but you can tell how much stuck (Doppler shift and that's about it). No telescopes were utilized at all, or in my memory even referred to, even though UT has two great ones right on campus! It put me off astronomy until about three years ago.

Thank you for taking the time to explain all that. I know it took some effort. I appreciate it. Hope we get to hang out soon.

[Centaur]

Aug 13, 2012 7:47:56 GMT -6 Paulie pchris00 said:

...Patrick's "what?" looks like a smart@$$ remark, but I know he truly wanted to understand what we were discussing. Who better to ask here than you?

Now, can we all get along?

Paulie, I thank you as the thread initiator for providing that thorough explanation to Patrick. You are a wise man. However if I had done that for my brother, whom Patrick has met, he would have scolded me for elaborating on things he already knew and demanded that I focus on only what was new to him. So I normally begin discussions in succinct terms and wait to learn from the listener which specific details require enhancement. Those who do not fully spell out their needs often say to me, “Never mind, that’s more than I wanted to know.”

Perhaps at age 66 I’ve become a curmudgeon. But this was by no means the first time that a responder has in the briefest terms implied that a post of mine was not as comprehensive as he would like. So I felt it was time to put an end to that. Sorry if that was taken harshly. I’m pleased that Patrick now understands the science related to your thread and expressed appreciation for the effort you took to bring him up to speed. In future I’ll attempt to respond either in a more laid back manner or simply ignore certain comments. Yes, let’s all get along.

[Paulie pchris00]

Aug 13, 2012 8:45:28 GMT -6 patrickm said:

My college astronomy class was one of my least favorite classes in four years of school. I got an A, but you can tell how much stuck (Doppler shift and that's about it).

My astronomy classes were a blast. I started watching the sky naked eye five years ago, during the summer of 2007. By January 2008 I took ASTR 264, thinking I was going to learn the stars, and maybe celestial navigation. Nope. It was about the physics of light and nuclear fusion in stars, the processes that created the solar system, stellar evolution, galactic structure, the Big Bang, and the possibilities of how our universe might end. Awesome stuff. Had some math in it, and my teacher the first semester was a physics guy, and tried to push the math on us. Only one student in the class was going into engineering, though. The rest just needed a science credit, and ASTR 264 was the only thing that fit their schedule. And then there was me who just wanted to learn astronomy. How it fit into my plan to major in English, I didn't care. Mike let the math slide on our last test.

By the end of February, I had read the entire textbook, which covered both semesters. I was checking out books from the library to find a cool topic for my paper. (My paper was about finding the scale of the solar system, which conveniently let me read and write about Transits of Venus. I was obsessed with it even back then). The other students were coming to me for help, so I put together study sessions. That was how I first got started sharing astronomy with others.

By the time the fall semester rolled around, I had heeded Mike's last words to me, "You need to get a telescope."

Aug 13, 2012 8:45:28 GMT -6 patrickm said:

No telescopes were utilized at all, or in my memory even referred to, even though UT has two great ones right on campus! It put me off astronomy until about three years ago.

We weren't required to observe with a telescope, but we had to observe in some way for something like 5% of our grade. We had one class observation (I remember seeing Saturn that night, but I had seen it in Valpo University's 16" telescope about two weeks before. Seeing it again in an 8" was something of a let down. (I know, it's unfathomable that anybody could be let down by the Ringed Planet). There were alternate observing projects for those who missed the class observation, and of course, I worked on those, too. I did two out of the four alternate projects, thinking I could sell or trade them to a desperate classmate or two. Wound up using them myself for extra credit.

For the semester of ASTR 263 in the fall of 2008, I had a different teacher, who had little background in astronomy. He let me bring my Dob to class one night and lead our observation. It was my first audience with a telescope, and I was nervous, but excited. Those two classes planted the seeds for me to become the public astronomer that I am now. Well worth the student loan debt and no degree. Wait, not really, but it was a great time for me. I kind of figured out what I wanted to do, just not how to make money at it.

Aug 13, 2012 8:45:28 GMT -6 patrickm said:

Thank you for taking the time to explain all that. I know it took some effort. I appreciate it. Hope we get to hang out soon.

You're welcome. Yes, soon.

[Paulie pchris00]

Aug 13, 2012 11:50:32 GMT -6 Centaur said:

Paulie, I thank you as the thread initiator for providing that thorough explanation to Patrick. You are a wise man. However if I had done that for my brother, whom Patrick has met, he would have scolded me for elaborating on things he already knew and demanded that I focus on only what was new to him. So I normally begin discussions in succinct terms and wait to learn from the listener which specific details require enhancement.

A reasonable approach.

Aug 13, 2012 11:50:32 GMT -6 Centaur said:

Perhaps at age 66 I’ve become a curmudgeon. But this was by no means the first time that a responder has in the briefest terms implied that a post of mine was not as comprehensive as he would like. So I felt it was time to put an end to that. Sorry if that was taken harshly. I’m pleased that Patrick now understands the science related to your thread and expressed appreciation for the effort you took to bring him up to speed. In future I’ll attempt to respond either in a more laid back manner or simply ignore certain comments. Yes, let’s all get along.

I have to admit, just about the only time I'm not sarcastic is when I'm discussing astronomy. What I know best is that there is an awful lot that I don't know. Plus, it's hard to put anybody down when I realize how insignificant I am to the universe.

[Centaur]

Since we are elaborating on illumination variances of the Moon at a particular “age” during different months, I’ll add one more factor that I failed to mention before out of respect for brevity. This does not have much effect on the Moon when near quadrature (90° from Sun - first/last quarter position – Half Moon), but does for the days surrounding a Full or Dark (new) Moon.

The Moon’s geocentric ecliptical latitude oscillates between about ±5° over the course of a month. That is another consideration for determining the illuminated fraction of the Moon’s apparent disk. It’s particularly relevant for New Moon spotters this month, since the waxing crescent Moon will be well south of the ecliptic.

I’ll soon be posting my August New Moon spotting challenge. While the aforementioned factor will enhance the young Moon's illumination percentage, it will exacerbate the usual problem arising from the small angle at which the ecliptic strikes the horizon at sunset during this time of year. These factors will greatly delay the sighting of a young Moon this month. It will likely be about 3.5 days old before seen by naked eyes in Chicagoland.

[Paulie pchris00]

I also failed to mention the Moon's orbital inclination, not so much for sake of brevity, but of, what's the word? Ignorance. Not that I'm unaware, but I don't have much of an understanding as to how it factors in the percentage of illumination. Usually I can only tell if Luna is above or below the ecliptic by how the shadows are cast near the poles around full Moon.

[Centaur]

Aug 14, 2012 9:30:00 GMT -6 Paulie pchris00 said:

I also failed to mention the Moon's orbital inclination, not so much for sake of brevity, but of, what's the word? Ignorance. Not that I'm unaware, but I don't have much of an understanding as to how it factors in the percentage of illumination. Usually I can only tell if Luna is above or below the ecliptic by how the shadows are cast near the poles around full Moon.

During lunar-solar conjunction or opposition, it's possible for the Moon to appear more than 5° from the ecliptic. This prevents it's fraction of illumination from reaching 0% or 100%. At quadrature the separation is exactly 90° by both direct measurement and projection along the ecliptic, even it the Moon is at ecliptical latitude ±5°.

A third factor is the Earth's orbital speed. When the Earth is near perihelion the Sun appears to move faster than average against the background stars, and slower when the Earth is near aphelion. This further affects the angular speed at which the Moon appears to separate from the Sun.

[RobbW]

Curt, just wondering, how does the Sun appear to move faster against the background stars? I usually can't see background stars when looking at the Sun. I'm not trying to be facetious. I assume they must be referring to the projected or expected movement of the Sun with respect to the background stars, not actually visibly seeing the Sun against them, right?

[Centaur]

Aug 14, 2012 16:47:36 GMT -6 RobbW said:

Curt, just wondering, how does the Sun appear to move faster against the background stars? I usually can't see background stars when looking at the Sun. I'm not trying to be facetious. I assume they must be referring to the projected or expected movement of the Sun with respect to the background stars, not actually visibly seeing the Sun against them, right?

Yes. The ancients understood the basic concept and deduced the constellation/sign in which the Sun was located at any particular time of the year. At the Adler Planetarium sky show they'll display for you a darkened daytime sky with the Earth not rotating but its orbital speed greatly increased to demonstrate the Sun appearing to move against the background stars.

The point in this thread is how from an observer's perspective the Sun's apparent pace along the ecliptic affects the angular separation between the Sun and Moon.