Talk:Moon/Archive 7

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Luna vs. Moon (One More Time!)

Keraunos adjusted the article to read that the name is "Luna", not "Moon". This matter has been discussed several times in the past (see the archives 1, 2 and, in particular, 4), and the consensus has always been a firm bias to "Moon". I have reverted this change for now, and invite Keraunos to produce the references that back the assertions he wishes to place in this article. (In my opinion, reflected by the previous discussion, he has a very steep slope to climb: to my knowledge, there is no significant body of English scientific literature on the Moon that refers to it as "Luna", and outside of some Robert Heinlein (and others) fiction, the occurrence in common English is far below the noise floor.) mdf 15:46, 9 May 2007 (UTC)

Agreed. --Ckatz^chat_spy 18:09, 9 May 2007 (UTC)

Concur. Shimgray | talk | 18:22, 9 May 2007 (UTC)

Agree. Nick Mks 06:00, 10 May 2007 (UTC)

I have noted this practice on some astronomy blogs and it seems strange to most people who have commented on it elsewhere. Of course, it comes from the Roman goddess Luna, and if you are speaking a Romance language it is perfectly correct (ie: La Luna in Spanish). But it has never been used in English, even as a rare alternative form. English draws this word from the Germanic languages which formed the basis of Saxon Old English, hence the German Montag, for Monday. I have a stack of Astronomy books and magazines going back 25 years, and had never heard of this until very recently. With all due respect to Keraunos, I really think that this type of thing needs to be stopped because it will confuse readers. I might also mention that the next fad that has started on some telescope review blogs and forums is to say Sol instead of Sun. PrivateWiddle 17:48, 14 May 2007 (UTC)

Agree - Every other planet's natural satellite has a name, like Jupiter's Io and Europa. Our satalite has Luna as it's name. --James W. 13:20, 21 May 2007 (UTC)

Here is a link to an online dictionary [1]. Please search on "moon" and "luna". Lunokhod 22:11, 23 May 2007 (UTC)

Our moon does have a name. Our moon's name is Moon. Astroguy2 19:50, 3 June 2007 (UTC)

It's a strange thing. I would say Earth's only visible moon, to the naked eye that is, is un-named. Many would argue it's called Luna, but that's the Latin for the word moon. And as "moon" is given as a word for NS's (Natural Satellites) one could conclude "The Moon" is nameless. But, "Moon" could be the name for our NS, as it was given before we knew of the other NS's orbiting other planets. So using moon as a word for NS's could be incorrect.

See below as the other orbiting bodies are satellites and the moon may be a double planet, perhaps it does have a name... moon.

"Luna" is certainly strictly a poetical name, but the word "moon" should not be capitalized any more than "sun" or "universe" should be (but which WP does). It is not an actual name and therefore not a proper noun and is firmly established by publishers as uncapped. I'd like to know what authority Wikipedians are appealing to on this or if they are just making it up as they go along like a lot of other editorial conventions (like capitalizing animal terms and political titles). What's the name of our planet's atmosphere? "the Atmosphere"? How about our water table? "the Water Table"? --Tysto 16:22, 9 October 2007 (UTC)

IAU Website: Spelling of Names of Astronomical Objects --Ckatz^chat_spy 05:34, 10 October 2007 (UTC)

This is obviously a semantic problem. By convention, if “Moon” is capitalized it is a Proper Noun or name of an explicit thing, and “moon” is a generic or common noun referring to all such satellites . The reason moon, sun and water table are not capitalized more frequently is that in that in most contexts writers and readers will be ignoring the suns, moons and water tables of other planets, so it is regarded as pedantic to insist on capitalization. In brief, capitalization is employed where one needs to indicate that the item in question is a particular thing and not a category of things. One could argue that “opera house” should be capitalized because it signifies a particular sort of house, but if we were to take that line, we would end up capitalizing virtually all nouns, like the Germans do. Luna is a lovely and poetic name, but it is not widely known, and as such to include it would confuse readers, which is not the purpose of a general encyclopaedia. Most people around the world are not science fiction devotees or particularly interested in astronomy. To them, the Moon is that glowing orb seen at night, and it is of little consequence to them that is an example of other such moons around unseen planets. Myles325a 06:45, 10 October 2007 (UTC)

My opinion (which I one day believed to be the general scientific view, but I got lost along the way) is the following: a non-manmade object that revolves around a planet is called a natural satellite. Planet Earth (capitalised, since there is only one) has one natural satellite: (the) Moon. Stricltly speaking, there is no other object in the universe called Moon or moon. However, many people choose to use moon as a synonym for natural satellite. Nick Mks 07:16, 10 October 2007 (UTC)

I also find it weird to say the Earth's only satellite has no proper name. We called it moon long before we know other satellites of other planets. We just eventually use moon as a common name for any natural satellite, and satellite is now more commonly referred to artificial satellite. See also the explanation from NASA http://helios.gsfc.nasa.gov/qa_earth.html#moonname . ppa (talk) 08:23, 27 January 2008 (UTC)

double planet

The section "5 Orbit and relationship to Earth" discusses the double planet issue is a dismisive way, mentioning only why it may not be a double planet, without any explanation of why the controversy exists. This is unfair.

The moon is gravitationally attracted to the sun more than it is attracted to the earth. The moon is drifting away from the earth every year.

There is no mention of Issac Asimov's artile on "why is the moon so far out there" A link to the wikipedia double planet should be provided. 198.103.184.76 15:53, 28 August 2007 (UTC)c. priest198.103.184.76 15:53, 28 August 2007 (UTC)

The Moon's Recession Rate

The introduction cites reference [2] as stating the recession rate is 3.8 cm/yr, and the section entitled "Orbit and relationship to Earth" cited reference [41] as stating the recession rate is 4 metres per century. Since both references have the 3.8 number (and one is more specific--3.84) and not the 4 number, I changed "4 m" to "3.8 m" for the sake of internal consistency.

Also, since both reference [2] and [41] were only used for the recession information, I decided to eliminate them and replace them with a better reference, so now [2] and [41] are the same. Is there a way to change that or does Wikipedia always number references sequentially even if they are the same source? In other words, is it just the way Wikipedia works that one could have a reference section with the same reference listed 50 times? Redhookesb 06:43, 31 May 2007 (UTC)

Doesn't the potential energy of the Moon-Earth system increase as they grow farther apart? What is this reduction addressing in the lead? Either way it's confusing. Besselfunctions 06:54, 11 June 2007 (UTC)

I think Besselfunctions is right here. The movement of the moon away from the earth results in an increase in gravitaional potential energy. The loss of the earths rotational energy is the compensating factor. Effectively the distortion to the shape of the earth induced by the moon's tidal forces results in a net torque on the moon about the barycentre. This torque is in the direction of the moons rotation, so it results in an increase in the moon's orbital energy, which results in a larger orbit.Gordion 13:42, 21 August 2007 (UTC)

Helium3

The article is missing a reference to Helium3...

Some background info on He3 in the moon can be found on the Horizon pages of the bbc: http://www.bbc.co.uk/sn/tvradio/programmes/horizon/broadband/tx/moonsale/

Our photo is correct, lunar eclipse does not show curve of Earth.

The first lunar eclipse I saw as an adult, I was expecting to see the curve of the Earth move across the Moon, and that simply did not happen. The whole thing was much more shadowy. And, on thinking it over, it occurred to me, if we’re going to expect earlier peoples to have figured out that the Earth was a sphere, it was not going to be from this line of evidence! (And yes, the Moon was kind of reddish or orangish, but I wouldn’t exactly call it blood red.)

Please look at our picture of the March ’07 lunar eclipse, there’s not really much of a curve at all.

Now, our article does not claim a curve, but this might be enough of a common misconception to be worth including and discussing. And we might also want to jazz up our “Human understanding” section. I mean, was Anaxagoras really the first to have a early scientific understanding? How about the Hindus and/or the Native Americans? Or the people who built Stonehenge in England, yeah, they may have believed a bunch of mystical stuff, but they may have also had a pretty good understanding of how Sun, Earth, and Moon interacted. FriendlyRiverOtter 09:42, 11 June 2007 (UTC)

6R10DB9

This is just a "heads-up" to keep tabs on 6R10DB9, a temporary satellite of Earth [2] -- which if it proves to be a small asteroid (rather than moon-mission junk) may warrant at least a footnote in this article. — Eoghanacht ^talk 15:30, 25 June 2007 (UTC)

Gravity

The formatting on the gravity entry in the table on the right is... tricky. At first glance, it looks like there is no entry for gravity and the Equatorial Surface is its own category. As this is not directly editable, I could not fix it myself. Perhaps the table needs to be widened? Superdupergc 20:16, 26 June 2007 (UTC)

Moon in general

I have a few questions:Shaunthinks93 18:49, 1 July 2007 (UTC) 1. If craters are caused by asteroids or comets, how can there be craters on the side of the moon that is always facing the Earth?

2. Why when scanners, monitors, detectors are dropped on to the moon, does it clang as though being struck like a bell, this must mean it is hollow. On this website there is a section that shows the layers of the moon, how can there be all those layers if the moon is hollow?

3. This isnt a question, but, if the moon is actually a spaceship, and we are an expiriment, a kind of TV show, if you like, this would explain why there are craters on the front of the Moon: these are created when that spaceship was travelling through the universe to get here. also the Hollow clanging would be caused by the inside of the spaceship, where it is controlledand the aliens habitate.

People always think of aliens from other planets, solar systems, and galaxies, but never think of the one thing that is right next to us, always there, always patrolling, checking and we never even thought about that possibility... So just think about it, all the possibilities that there could be of the moon.

Shaunthinks93 18:49, 1 July 2007 (UTC)shaunthinks93

1. There are fewer craters on the side that faces the Earth, but it's not like the Earth is so large as to completely block all possible trajectories from space into the Moon's face. Many, but not nearly all, incident meteors/asteroids/&c. are blocked by the Earth.

2. They don't. They don't make any sound at all-- there is no atmosphere on the Moon to carry sound.

3. Did you forget to take your Risperdal? siafu 17:01, 2 July 2007 (UTC)

Some additional comments on points 1,2,3 above.

1.Some theories regard Jupiter as an important sentry of the outer solar system, in that it could have mopped up asteroids that would otherwise have collided with Earth. The Moon has been said to do the same thing with respect to Earth, and the Earth with the Moon. The effect of shepherding asteroids away from the near side of the Moon need not be dependant just on the bulk of the Earth intercepting asteroids that would otherwise have collided with the Moon. The Earth would interfere with the orbits of nearby asteroids, sending some of them off into deep space, just as Jupiter is said to have done with respect to the inner solar system. I had the notion that you could estimate when the Moon had adopted its current posture by mapping asteroid impacts on the near and far sides and comparing them. Theoretically, this might have given a better determination of the Moon’s age. I sent this to the Geology Dept at Harvard, who were interested enough to reply, but opined that the distribution figures would not be fine enough to make estimations statistically interesting.

2 Also had the notion that some such statistical survey on extraneous matter picked up by the leading edge of a satellite as it moves thru space. It ploughs through interplanetwry dust and stuff, and so there should be more of this on the leading edge. If the leading edge has changed over time, then distribution of such matter will also have changed, thus giving possible way of estimating when such changes of direction in orientation occured. (Btw, this is where I think there is a common confusion between "limb" and "leading edge".)

3.The Moon is airless and therefore there is no atmospheric sound, but sound can pass thru the mass of the Moon itself. I read somewhere that an impact on the Moon, possibly human-engineered had it ringing like a bell for months. Any one rem this? Of course Moon could be a hollowed out Death Star, and we could be hearing the engines etc of such a device.

4.Moon as alien space ship might explain why we see it as EXACTLY covering the Sun during solar eclipse, a phenomenon which otherwise has no scientific explanation.Myles325a 05:28, 9 July 2007 (UTC)

Actually, the moon sometimes covers less than the whole sun, sometimes more, sometimes pretty much exactly the whole sun. See solar eclipse for more details. --Slashme (talk) 13:20, 10 January 2008 (UTC)

COST OF EXPLORATION

How much would a privately funded moon mission cost and who are the likely backers —Preceding unsigned comment added by 69.125.110.223 (talk) 17:20, August 30, 2007 (UTC)

Why one side always faces the Earth?

I find a different answer from what our article says, and an answer from a seemingly good website, and one that seemingly makes sense. “This synchronous rotation is caused by an unsymmetrical distribution of mass in the Moon, which has allowed Earth's gravity to keep one lunar hemisphere permanently turned toward Earth” [3] .

Our article says, “Early in the Moon's history, its rotation slowed and became locked in this configuration as a result of frictional effects associated with tidal deformations caused by the Earth.[6]”

Now, perhaps both could be contributing causes. Please help with this if you can. FriendlyRiverOtter 19:08, 2 July 2007 (UTC)

The first one is not exactly correct; tidal locking does not require an asymmetric distribution of mass. The moon may have such an asymmetric distribution, but this also happens as a result of tidal locking and need not be a cause. siafu 21:36, 2 July 2007 (UTC)

And that might explain why other satellites in the solar system have this same one-side-facing-only relation to their planet. Next question, why is it 59% of the moon that we can see? FriendlyRiverOtter 03:35, 19 July 2007 (UTC)

WILL the moon get lop sided over time? due to centrifugal force —Preceding unsigned comment added by 69.125.110.223 (talk)

The material on the far side experiencing greater "slinging"? Maybe. I can kind of see that as a possibility. And since one side is always the far side, maybe over time there is a cummulative effect. And I am learning that many (most?) astronomical items are not perfectly symmetrical. FriendlyRiverOtter 08:23, 14 September 2007 (UTC)

The moon isn't exactly in tidal lock: it librates around the equilibrium, torqued by forces other than the Earth's point-mass potential. The moon is also not symmetric in its shape, as a result of the tidal forcing. Hence we can see 59% of the surface. For a better discussion, see tidal locking or any standard intro. astronomy text. Further discussion here is not appropriate. Michaelbusch 08:27, 14 September 2007 (UTC)

Oh, Michael. Why? Many of our articles end up not really explaining anything, not really teaching anything, not really describing anything. Our articles mainly just mention things and refer elsewhere. We seem to have rules that stand in the way of narrative flow and natural human language.

Exactly what you explained about libration would be good to include in the article itself! And as long as we keep our article divided into sections we need not worry about length, for people can read what they're interested in, and not read what they're not.

I should learn something from reading a wikipedia article, and often I do not. FriendlyRiverOtter 17:14, 14 September 2007 (UTC)

Equatorial circumference

If the equatorial radius is correct at 1,738.14 km, wouldn't the equatorial circumference be 10,921 km, not 10,916 km? 10,916 would appear to be based on a 1,737.4 figure for the equatorial circumference which various references give. I know the moon's not a perfect geometric shape, so I can't assume that 2πr necessarily holds in this case, but the source for 10,916 km does use the 1,737.4 figure (×πr = 10,916.4)...--Father Goose 07:51, 13 July 2007 (UTC)

The Earth from The Moon.

Some people are consistent to believe that "The Great Wall of China" is the only man-made object visible from The Moon. However, if I, or you were to be standing on the moon right now, and took a glance over to where Earth is, you would just about be able to make out the continents.

The moon is over 400,000 km away, seeing anything man-made on the earth, with the naked eye, would be almost impossible (but the object would have to be rather large, as in, starting on Earth, then leaving it. If such a thing could be made, think of an elevator "into space") Many confuse it with 'space'. 'Space' starts about 100km from the surface, and quite a lot can be seen from here. Things like motorways (highways), ships on the sea, cities and even a few individual buildings. Of corase the further out into space you go, the less you'll be able to see.Jamiepgs 15:56, 16 July 2007 (UTC)

Jamie please sign your posts by typing ~~~~ and could you explain what your point is? "Space" is a pretty undefined term as even 100km up you are still in the heliosphere. Each area of "space" tends to have its own technical term such as interstellar medium . As for what is visible from the moon - I've never actually checked it but it is generally accepted that the great wall of china is the only man made object visible from there. The point is not what can be seen from "space" but what is seen from the moon as that is what this article is about. Talk pages are only here to discuss potential changes to the article and should not be used to float vague ideas. Sophia 15:42, 16 July 2007 (UTC)

OK, then I suggest that this could be added...

Although it's accepted, it doesn't make it any less false. Claiming that The Great Wall of China is the only man-made object on Earth, visible from the moon with the naked eye would be making a false statement. [4] The point I was making was that people confuse it with what you can see from Space, as in its early reaches from our surface it is visible. Jamiepgs 15:56, 16 July 2007 (UTC)

I see now what you are saying and you are correct that it is false - this is a better source [5] for that fact. The point that you are making about confusing visability distances doesn't really belong here and I'm scratching my head to think where it would go. This would count as WP:Trivia and I'm not sure it really adds anything. The moon is a fascinating structure who's formation and composition are not really understood and these are the areas this article focuses on. The moon dust was an interesting fact as it enabled us to relate it to everyday things making the facts more accessible but this I feel does not improve the article. Sorry to be so negative and don't let it put you off making suggestions. You are doing the absolutely right thing by discussing this here and suggesting changes so we can all chip in. Sophia 17:06, 16 July 2007 (UTC)

At night, could you see the lights of large cities, or the burning flares of natural gas fields (if that practice is still used)? FriendlyRiverOtter 22:49, 13 September 2007 (UTC)

Etymology

I haven't been here in a while, and was surprised to see that there is now a section "Etymology". While this might help clarify these idiotic Luna-Moon discussions, the description appears to be incorrect. In particular, is it not true that the generic name "moon" is based upon the proper name "Moon" of Earth's natural satellite? Wasn't the Moon discovered and named before the other "moons" of our solar system? When people gave the name "Moon" to our natural satellite, did they do so with the knowledge that other "moons" existed, and hence that the name was generic and not proper?

Thus, I propose changing this sentence

The Moon has no formal English name, although it is occasionally called Luna (Latin for "moon") to distinguish it from the generic "moon" (referring to any of the various natural satellites of other planets).

to (or something similar)

The proper english name of Earth's natural satellite is the Moon, though it is occasionally called Luna (Latin for "moon"). The name Luna has never been formally recognized by any international organization, and its use in the popular and scientific vernacular is extremely rare. The generic word "moon", which refers to any of the various natural satellites of other planets, is derived from the name of Earth's only natural satellite. The confusion between the proper noun Moon (which is sometimes, though not always, captitalized) and the generic word moon has led some to argue that the Earth's natural satellite has no official english name. Lunokhod 10:40, 17 August 2007 (UTC)

Yeah, that section needed work. I took a hack at it.--Father Goose 19:30, 17 August 2007 (UTC)

Thanks for doing that. I've tweaked it a bit, primarily to move the third sentence into first place for a more formal definition. --Ckatz^chat_spy 05:44, 18 August 2007 (UTC)

I agree entirely. I'm also removing the Latin name in brackets in the opening sentence, because this is an English-language dictionary and the names of the Moon in the thousands of other human languages are irrelevant. Luna is discussed further down the article, and that's fine. But it has no priority over any other non-English name. -- JackofOz 06:31, 7 September 2007 (UTC)

I've reverted that change - "Luna", while not the English name, does get used frequently and a mention in the lead is relevant and justifiable (as with "Sol" at Sun). In this case, Latin does take priority over other languages as "Luna" is directly related to numerous English words ("lunar" etc.), many of which are used in this article. --Ckatz^chat_spy 08:10, 7 September 2007 (UTC)

I'm still not happy with that. Just because we mention Sol on the Sun's page does not, of itself, justify this. If Luna is used frequently, we should explain that use - not just say that the Latin name for the Moon is Luna, as if that bald fact was notable. It currently reads as if English-speakers are also Latin-speakers, who would obviously want to know this information. This is like the article for "Table" starting out with "A Table (Latin: mensa) is a piece of furniture that ... ". -- JackofOz 08:43, 7 September 2007 (UTC)

I see the sense of both arguments but more strongly agree with removing Luna in the first sentence. However, given the tiny amount of real estate we're talking about here, this threatens to go into WP:LAME.--Father Goose 09:23, 7 September 2007 (UTC)

Main page

oh my gosh, how did all those linked solo years get by FAC[6]? And there are month-year combos incorrectly linked as well. Solo years need not be linked, per WP:CONTEXT, WP:MOSLINK. Delinking them all will take forever; can someone help? They're even linked in the refs. Also, there are See also templates at the bottom of sections; per WP:LAYOUT they should be at the top. And portals belong in See also, per WP:LAYOUT. Also, there are spaced emdashes throughout the text, against WP:DASH. Normally I run through and correct these things before mainpage, but there's more work here than I'm accustomed to. SandyGeorgia (Talk) 22:21, 17 August 2007 (UTC)

Wow, I thought main page featured articles were particularly better than the others, and could at least follow style guidelines. Fault is the person who selected this to be on the main page. ~ UBeR 01:57, 28 August 2007 (UTC)

The selection may have been event-based--at the moment, as I write this, a lunar eclipse is occuring literally right outside my front door. --JB Adder | Talk 10:54, 28 August 2007 (UTC)

This article now contains two fact tags as well. - Face 16:34, 28 August 2007 (UTC)

eclipse section

i have taken this part out from eclipse section as that information is irrelvant to moon The next solar eclipse takes place on September 11, 2007, visible from southern South America and parts of Antarctica.The next total solar eclipse, on August 1, 2008, will have a path of totality beginning in northern Canada and passing through Russia and China. if i have done wrong I am sorry please put it back

Information such as this quickly becomes outdated and frivolous. You were right to remove it. Encyclopedias should take into consideration the historical context of what they're writing, rather than focus on non-important, albeit recent, events. ~ UBeR 01:59, 28 August 2007 (UTC)

I agree with UBeR that such temporal information goes out of date quickly. However, Wikipedia is dynamic enough to replace it with updated information when appropriate. To say that solar eclipses have nothing to do with the moon is like saying your reflection has nothing to do with the mirror - true in its way, but if it weren't for the mirror the reflection wouldn't exist! As to whether the info should be included, I'm slightly in favour of putting it back. --King Hildebrand 19:14, 29 August 2007 (UTC)

Good work getting this to the front page

Nice work folks :) Kidshare 07:37, 28 August 2007 (UTC)

I won't edit the article since it is on the front page, but shouldn't "...Apollo program has achieved the first (and only) manned missions to date..." read "...Apollo program has achieved the first (and to date, only) manned missions...", or similar. As it is, it implies that we may one day discover that the Apollo missions were not the first manned missions. I enjoy a good conspiracy theory, but no need to codify them in a reference work. Travis Garris 17:29, 28 August 2007 (UTC)

Travis's modification allows for humanity's return to the moon, but I don't see how either wording implies or fails to imply that the Apollos didn't land there. What am I missing?--King Hildebrand 19:09, 29 August 2007 (UTC)

• I particularly liked how the article was on the front page on the day of a lunar eclipse here in New Zealand.Lisiate 22:54, 28 August 2007 (UTC)

Errrm - unlike solar eclipses, lunar eclipses are visible wherever the moon is above the horizon - a whole hemisphere at a time. NZ was not uniquly blessed on this occasion. The moon is in the earth's shadow wherever you view it from.--King Hildebrand 19:09, 29 August 2007 (UTC)

Green cheese

How how in the world did the whole "moon is made of green cheese" saying start? --24.249.108.133 06:25, 29 August 2007 (UTC)

Well, it is. Didn't the scientist go to the Moon and check that? Winston.PL 14:07, 2 October 2007 (UTC)

Now that is a nice question.--Father Goose 07:16, 29 August 2007 (UTC)

Centripetal tides

It's not the centripetal force that generates tides. It's the gravitational differential between the centre of the earth or moon and its surface. The side of the earth facing the moon is pulled more strongly than the centre, causing a hump in the water on that side. Less obviously, the side away from the moon is pulled less strongly than the centre, so the water is "left behind" as the body of the earth is pulled out from underneath. The effect would exist in the absense of rotation. A similar tidal effect is felt on the moon, which is:

• greater due to the stronger gravity of the earth
• smaller because of the smaller radius of the moon, and
• less obvious because the moon has no easily deformable masses of liquid on its surface.

--King Hildebrand 19:01, 29 August 2007 (UTC)

Newton's well known explanation of the tides would only be valid in the absense of continents, as mentioned in the article on the physics of tides. In fact the tidal range in the middle of oceans is very small, and is only large on continental shelves. This is explained in R E Craig's book Marine Physics. It is more useful to think of the oceans as odd shaped, interlinked bowls of water, the tides being caused by the diurnal wobbling of the bowls and the effects of gravity on the water in the bowls.

As Craig explains, the resultant of solar & lunar gravity pulls the oceans horizontally, contributing to the resonant waves that cause the oceans to slosh about in their basins. The vertical effect (i.e. "the hump") is negligible.

While the WP article on tides does not say this in so many words, it is consistent with info in the article. Thus, while statements like "causing a hump in the water on that side" etc is common knowledge, I understand that it is completly wrong! I think this should be mentioned here and in the article on Tides. --GilesW 22:05, 29 August 2007 (UTC)

King Hildebrand is absolutely 100% correct. As it is currently written, saying “centripetal forces cause tides” is pretty much like saying “gravity causes tides.” That much is obvious. However, giving this sort of explanation is worse than saying nothing. The concept of “tides” are now so well entrenched in physics, that any force that varies significantly in magnitude across a distance is known as a “tidal force.” For instance, the effect of being stretched as ones body falls into a black hole (whereby ones feet are pulled more strongly that ones head) is a tidal force or tidal effect.

I can understand also what GilesW is saying but I think the text he's defending doesn't explain his point well at all. Fine, the actual “hump” caused directly by the tidal force is relatively small and is magnified by Earth's rotation, basins, harmonics, etc. We know this because some places, like the Bay of Fundy, see exaggerated effects while others see attenuated effects. Nevertheless, if the Moon were very far away but extremely massive so 1) the barycenter was completely outside the Earth, and 2) the tidal force was near-nonexistent, there would be near-zero “hump” for these other effects to magnify and we would experience no ocean tides.

I don't like making waves (no pun intended) because I don't like to make significant changes to articles the first time I visit them. I've got enough battles on my hands doing slash & burn on other articles. But someone who gives a damn about this article should fix this. An article on the Moon for God's sake, should at least have the issue of tides properly explained.

I would propose something along the lines of as follows (I don’t know how to truncate this into a tight, pithy intro version):

“ Ocean tides are initiated by the tidal force of Moon’s gravity and are magnified by a host of effects in Earth’s oceans. The gravitational tidal force arises because the side of Earth facing the Moon (nearest it) is attracted more strongly by the Moon’s gravity than is the center of the Earth and—even less so—the Earth’s far side. The gravitational tide stretches the Earth’s oceans into an ellipse—with the Earth in the center. The effect takes the form of two bulges—elevated sea level—relative to the Earth: one nearest the Moon and one farthest from it. Since these two bulges rotate around the Earth once a day as it spins on its axis, ocean water is continuously rushing towards the ever-moving bulges. The effects of the two bulges and the massive ocean currents chasing them are magnified by an interplay of other effects; namely frictional coupling of water to Earth’s rotation through the ocean floors, inertia of water’s movement, ocean basins that get shallower near land, and oscillations between different ocean basins. The magnifying effect is a bit like water sloshing high up the sloped end of a bathtub after a relatively small disturbance of one’s body in the deep part of the tub. ”

This, at least, is the full explanation as far as I know it. How one gets that into a compact treatment is beyond me.

Greg L (my talk) 04:39, 1 September 2007 (UTC)

I agree with King Hildebrand and Greg L. I am a physicist, and that "centripetal forces ... barycentre" sentence just baffled me. And if it baffles me, I can't imagine it does much for a non-scientist, so I'm glad it's gone. I do realize now that the picture that was in my head-- the ocean bulges oriented with the moon--was really incomplete. The Moon article made me face that, which is an example of why Wikipedia is so great. But unless the "good" explanation can be made in a few sentences, it's better just to show the bulges, followed by a disclaimer that the continents and rotation make it much more complicated -- the way it stands right now isn't bad. Someone wanting the full picture can go to tides. (However, for some really incomprehensible prose, take a look at the second paragraph of Tides#Tidal_forces -- yikes!). Spiel496 15:19, 2 September 2007 (UTC)

Albedo and Retroreflection

It is well known that the moon is much brighter when it is full, i.e. when the earth is almost between it and the sun. The bright areas of the moon's surface exhibit retroreflection due to the opposition effect, like those projection screens that are coated with small glass beads. This causes the changes of albedo with phase of the moon. Retroreflection This effect causes the halo round the shadow of the astronaut's head reflected in his visor in the well known moon-walk photograph of Aldrin (in the Article), and acts as a fill-in light for the shadow side of objects & people on the moon.

Should not this be mentioned? Has moon dust been shown to be retroreflective? --GilesW 07:34, 30 August 2007 (UTC)

Check out Opposition effect. Lunokhod 23:26, 30 August 2007 (UTC)

Thanks. Are the above changes better, or is it technically incorrect to refer to 'opposition effect' as 'retroreflection'? GilesW 02:13, 1 September 2007 (UTC)

I have checked out opposition effect. 'The usual major cause of the effect' is ascribed to 'shadow hiding'. However the article does not mention other causes of the effect on the moon. It seems evident that the brightest areas on the full moon associated with new craters are too bright to be accounted for by shadow hiding, and that this can only be due to the retroreflection of sunlight by the well known glass spherules found on the lunar surface, i.e. the heiligenschein effect. I presume that this is addressed elsewhere, but cannot find anything about it on the web. GilesW 10:15, 14 September 2007 (UTC)

Opposition surge doesn't require glass spherules. It is a characteristic of most granular media. Consider that if I have a random distribution of grains, some fraction of them will be distributed into configurations that retro-reflect (e.g. three faces of a cube). See the work of Bruce Hapke, among others. Hapke's scattering models aren't 100% accurate, but they are a start. Michaelbusch 16:37, 14 September 2007 (UTC)

Opposition surge may not require glass spherules, but NASA tells us that they are there in this web page: glass spherules. (Revised GilesW 20:18, 18 September 2007 (UTC))

• I request that any local contribution that the glass spherules heiligenschein makes to opposition surge should be described, or the absence of any such contribution should be explained. GilesW 19:56, 18 September 2007 (UTC)

• Is the brightness of the rims and bowls of some craters an opposition effect, and if so, has it been determined whether or not this is due to glass spherules? GilesW 19:56, 18 September 2007 (UTC)