Talk:Libration

message: The article would benefit if molecular libration was also explained.
--Mfrosz 06:44, 25 July 2006 (UTC)
replies: text: No, that's a separate topic, now moved to Libration (molecule).--Jerzy•t 07:06, 6 September 2010 (UTC)
thread_title:  Molecular libration 

message: === 59% ===
It would be nice if the article stated where this number comes from. I'd have a stab at some approximate calculations, but I'm busy right now. Shinobu 16:14, 14 April 2007 (UTC)
replies: text: This number doesn't come with any accompanying calculations because I am quite sure it'd be a complex formula. Both NASA and ESA use this number in their moon info publications, so I imagine that should satisfy any question of the number's value. As for how it's calculated, maybe contact a boffin at NASA. Links: ESA - Moon  and NASA - Moon. 130.102.44.52 (talk) 04:55, 14 October 2008 (UTC)

text: It's probably an integral of some sort, knowing the horizontal and vertical variations. Tom Ruen (talk) 15:44, 14 October 2008 (UTC)

text: This is not an important effect: according to the Wolfram Alpha page "Angle subtended by the Moon when viewed from the Earth", that number was less than 0.6 of a degree at the time the server prepared its response to me (it should vary ±10% over the month), and my view of a full moon would have been short of 180° by that small angle. The full moon loses illumination (at 360° per lunar cycle) from about that much of its surface in about 40 minutes. (The effect thus entails making the apparent full moon about 40 minutes longer!) This is not at all relevant to how much of the moon's surface can be mapped without sending something far enuf out: the mapping from earth is cumulative, and the diurnal libration is sufficient to wipe out this parallax-related issue's effect on mapping.   Taking note of the effect is moderately clever; for those a speck cleverer than that, it may induce the desire for the numbers i've furnished. (I invest my cleverness elsewhere, and for me the numbers' only value is their relevance to what should be in the article.) My read is that interest directly in the cited phenomenon is sufficiently narrow that it applies to professional astronomers (those happy few), perhaps astronomy students, and probably dedicated amateurs: i.e., IMO it is probably not fodder for a general-purpose encyclopedia.   BTW, "How long is the moon really full?" is a related question (IM-offhand-O more interesting and thus the best reason for considering inclusion of the restricted view of the moon), and the sun subtends (from earth and, shall i say, to the moon) an angle about 10% less than the moon from the earth. (Note that one answer is "only an instant", focusing on monthly maxiumum illumination of either the instantaneous near hemisphere or the median near hemisphere.) Offhand, i think that means that at the moment in each lunar cycle when the three bodies are closest to alignment, the Moon appears full at solar midnight (i.e., at the longitude where sunset is as far in the past as sunrise is in the future), but simultaneously, at the longitudes where sunset or sunrise is occurring, appearing full is either recently over or soon to start (not necessarily respectively; i'm getting tired of getting such details right). That could BTW be worth a passage in a science-fiction novel that involves separated lovers, or precision treatment of lycanthropy!--Jerzy•t 19:36, 9  & 08:07, 10 September 2010 (UTC)
replies: text:    My clumsy language (in the last of those 3 'graphs) re a core instant of full moon deserves rewording. It reflects my attempts to stand in, with the math and physics, where only colleagues lacking those tools had previously ventured re the fraction -- perhaps also lacking (as i do) adequate command of much astronomy-specific background.   My wording "maximum illumination of ... the instantaneous near hemisphere" (which actually echoes the fact that my parents had no idea why the kids'-TV-show demonstration of the three-body explanation of lunar phases didn't also imply monthly lunar and solar eclipses) should have referred centrally to the instant of closest alignment among sun, a moon longitude, and either the earth as a whole or the observer, since the sun (duh) is not emerging from behind the earth and rapidly increasing its illumination. That maximum of illumination would, i'm pretty sure, be so "broad" and thus at the mercy of subjective judgments as to be an observation useless for predicting future observations, and its use as a reference pointless.   All that said, alignment to the median longitude (or, on reflection, rather the mean, which presumably converges faster in the face of random censoring of rare amd crucial extreme observations by bad weather or inaccessibility of desirable earth longitudes) (in any case, to be recognized relative to surface features) or to the center of the disk, may nevertheless both be workable conventions; the accompanying article should identify the accepted or predominant one. (That convention may already be stated in other articles.)--Jerzy•t 08:07, 10 September 2010 (UTC)

text: Consider the right triangle formed by the Moon's center (C), your eye (E), and the limb of its apparent disc (L, the right angle).  Clearly the angle ECL is short of a right angle by CEL, the angular radius of the moon in your sky, which is about a quarter degree. —Tamfang (talk) 22:13, 11 September 2010 (UTC)
thread_title:  (Adjustments to visible area) 

message: It would be nice if the article stated where this number comes from. I'd have a stab at some approximate calculations, but I'm busy right now. Shinobu 16:14, 14 April 2007 (UTC)
replies: text: This number doesn't come with any accompanying calculations because I am quite sure it'd be a complex formula. Both NASA and ESA use this number in their moon info publications, so I imagine that should satisfy any question of the number's value. As for how it's calculated, maybe contact a boffin at NASA. Links: ESA - Moon  and NASA - Moon. 130.102.44.52 (talk) 04:55, 14 October 2008 (UTC)

text: It's probably an integral of some sort, knowing the horizontal and vertical variations. Tom Ruen (talk) 15:44, 14 October 2008 (UTC)
thread_title:  59% 

message: Also, because the ratio of the moon's diameter to its distance from earth is non-negligible, at any given moment an earth observer can see slightly less than half the surface.  —Preceding unsigned comment added by 131.193.179.146 (talk) 03:10, 4 October 2007 (UTC)
replies: text: This is not an important effect: according to the Wolfram Alpha page "Angle subtended by the Moon when viewed from the Earth", that number was less than 0.6 of a degree at the time the server prepared its response to me (it should vary ±10% over the month), and my view of a full moon would have been short of 180° by that small angle. The full moon loses illumination (at 360° per lunar cycle) from about that much of its surface in about 40 minutes. (The effect thus entails making the apparent full moon about 40 minutes longer!) This is not at all relevant to how much of the moon's surface can be mapped without sending something far enuf out: the mapping from earth is cumulative, and the diurnal libration is sufficient to wipe out this parallax-related issue's effect on mapping.   Taking note of the effect is moderately clever; for those a speck cleverer than that, it may induce the desire for the numbers i've furnished. (I invest my cleverness elsewhere, and for me the numbers' only value is their relevance to what should be in the article.) My read is that interest directly in the cited phenomenon is sufficiently narrow that it applies to professional astronomers (those happy few), perhaps astronomy students, and probably dedicated amateurs: i.e., IMO it is probably not fodder for a general-purpose encyclopedia.   BTW, "How long is the moon really full?" is a related question (IM-offhand-O more interesting and thus the best reason for considering inclusion of the restricted view of the moon), and the sun subtends (from earth and, shall i say, to the moon) an angle about 10% less than the moon from the earth. (Note that one answer is "only an instant", focusing on monthly maxiumum illumination of either the instantaneous near hemisphere or the median near hemisphere.) Offhand, i think that means that at the moment in each lunar cycle when the three bodies are closest to alignment, the Moon appears full at solar midnight (i.e., at the longitude where sunset is as far in the past as sunrise is in the future), but simultaneously, at the longitudes where sunset or sunrise is occurring, appearing full is either recently over or soon to start (not necessarily respectively; i'm getting tired of getting such details right). That could BTW be worth a passage in a science-fiction novel that involves separated lovers, or precision treatment of lycanthropy!--Jerzy•t 19:36, 9  & 08:07, 10 September 2010 (UTC)
replies: text:    My clumsy language (in the last of those 3 'graphs) re a core instant of full moon deserves rewording. It reflects my attempts to stand in, with the math and physics, where only colleagues lacking those tools had previously ventured re the fraction -- perhaps also lacking (as i do) adequate command of much astronomy-specific background.   My wording "maximum illumination of ... the instantaneous near hemisphere" (which actually echoes the fact that my parents had no idea why the kids'-TV-show demonstration of the three-body explanation of lunar phases didn't also imply monthly lunar and solar eclipses) should have referred centrally to the instant of closest alignment among sun, a moon longitude, and either the earth as a whole or the observer, since the sun (duh) is not emerging from behind the earth and rapidly increasing its illumination. That maximum of illumination would, i'm pretty sure, be so "broad" and thus at the mercy of subjective judgments as to be an observation useless for predicting future observations, and its use as a reference pointless.   All that said, alignment to the median longitude (or, on reflection, rather the mean, which presumably converges faster in the face of random censoring of rare amd crucial extreme observations by bad weather or inaccessibility of desirable earth longitudes) (in any case, to be recognized relative to surface features) or to the center of the disk, may nevertheless both be workable conventions; the accompanying article should identify the accepted or predominant one. (That convention may already be stated in other articles.)--Jerzy•t 08:07, 10 September 2010 (UTC)

text: Consider the right triangle formed by the Moon's center (C), your eye (E), and the limb of its apparent disc (L, the right angle).  Clearly the angle ECL is short of a right angle by CEL, the angular radius of the moon in your sky, which is about a quarter degree. —Tamfang (talk) 22:13, 11 September 2010 (UTC)
thread_title:  50% 

message: According to this source, the moon also wobbles slightly about its centre of gravity. Shouldn't something about his be included in the article? Kelisi 01:13, 22 July 2007 (UTC)
replies: text: The current text of the article (as at 27 January 2019) seems to be misleading.  The introduction to the article says that libration is due to 'three mechanisms detailed below, two of which are causing a relatively tiny physical libration...'  But as far as I am aware, none of the three mechanisms described are 'physical', because they are all due to the different angles at which the moon is seen from the earth, not to any motion of the moon itself.  There are some genuine physical 'wobbles' of the moon, but these are very slight, and at present they are not described in the article.109.150.6.143 (talk) 11:24, 27 January 2019 (UTC)
thread_title:  Physical libration 

message: I am unhappy about this explanation, and about the analogy with the seasons. Since there is tidal locking, the same polar tilt should be exhibited at all times (all things being equal, i.e. if we ignore the OTHER types of libration listed). In other words, the 59% arises from the other types, with this one not contributing.  — Preceding unsigned comment added by 92.2.211.127 (talk) 13:24, 24 October 2012 (UTC)
replies: text: The tidal lock determines the period of the rotation, but has not yet fixed its axis. —Tamfang (talk) 06:36, 23 April 2023 (UTC)
thread_title:  Latitude libration 

message: The article should mention whoever it was that discovered lunar librations. —MiguelMunoz (talk) 00:30, 4 September 2010 (UTC)
replies: text: It came pretty early; i think Brahe first mapped the range of the variability of the longitudinal limbs, but i'm not sure the Arabs didn't note the effect before telescopes.--Jerzy•t 08:24, 6 September 2010 (UTC)
thread_title:  History 

message: There doesn't seem to be any discussion as to the cause of lunar libration. Might it be due to gravitational waves, as have recently been proven experimentally? - Paul2520 (talk) 13:25, 18 March 2016 (UTC)
thread_title:  Gravitational waves? 

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thread_title:  External links modified 

message: The 6.7 degrees should be visible to the unaided eye.  — Preceding unsigned comment added by 2A00:23C0:7C80:8401:981D:286D:6C7:9A8D (talk) 16:50, 18 June 2018 (UTC)
replies: text: Harriot might have made the discovery some decades before Galileo. See http://rsnr.royalsocietypublishing.org/content/63/2/163  — Preceding unsigned comment added by 2A00:23C0:7C80:8401:981D:286D:6C7:9A8D (talk) 16:58, 18 June 2018 (UTC)
replies: text: Thanks for spotting, added caveat. Brandmeistertalk   17:23, 18 June 2018 (UTC)
replies: text: 7.7 degrees is about the same as 6.7 degrees.  — Preceding unsigned comment added by 86.179.131.222 (talk) 10:28, 19 June 2018 (UTC)
thread_title:  Visible 

message: I do not have a planetarium program but such a program might be able to generate an image of a full year's libration as one graph.  The position in the moon's sky of the Earth as seen from the center of the near side of the moon should be recorded by its Cartesian coordinates for 365 or more positions in the year and the points connected by a drawn curve which would be a graph of libration.  The citation for the image could be the name of the planetarium program.  I for one would like to see the graph.  - Fartherred (talk) 17:19, 8 June 2019 (UTC)
thread_title: Libration of the moon as seen from the moon

message: I just created a new page for libration point orbit, associated of late with the JWST. 
My mission was merely to cover a small, evident gap, but for as long as I attended to this, I came to the impression that this page should be renamed lunar libration and a top level libration page (not necessarily as reductive as a dab) could dispatch the various weakly related libration subpages. It's somewhat problematic in this instance that celestial mechanics is shot through with various and sundry libratory jitterbugs, lunar libration merely being the most parochial. 
Just a suggestion based on short contact. — MaxEnt 23:34, 20 September 2022 (UTC)
thread_title:  Libration point orbit.