Talk:Moon

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In the leap years 1801-2500 February has three phases instead of four phases of the Moon, or a phase is just on leap day.[edit]

In the leap years 1801-2500 February has three phases instead of four phases of the Moon, or a phase is just on leap day. Source http://astropixels.com/ephemeris/phasescat/phasescat.html

1820 FM on leap day
1824 NM on leap day
1856 LQ on leap day
1860 FQ on leap day
(1900 NM on 1 March because 1900 is not a leap year!)
------------------------------
1936 FQ on leap day
1940 no LQ
1972 FM on leap day
1976 NM on leap day
2008 LQ on leap day
2012 no FQ
2048 FM on leap day
2052 no NM
2088 FQ on leap day
2092 no LQ
-------------------------------
2124 FM on leap day
2128 no NM
2164 FQ on leap day
2168 no LQ
2196 NM on leap day
------------------------------
2228 LQ on leap day
2232 no FQ
2268 FM on leap day
2272 NM on leap day
------------------------------
2304 LQ on leap day
2308 FQ on leap day
2312 no LQ
2344 FM on leap day
2348 no NM
2380 LQ on leap day
2384 no FQ
2416 NM on leap day
2420 FM on leap day
2424 no NM
2456 LQ on leap day
2460 FQ on leap day
(2500 NM on 1 March because 2500 is not a leap year!)
You can easily see that there are pairs or even trios after each about 40 years! And NM/FM and FQ/LQ are alternately!  — Preceding unsigned comment added by 84.245.24.147 (talk) 14:38, 11 February 2016 (UTC) 
Why is this here?  Who really cares about the relationship of moon phases to leap days? 71.93.61.178 (talk) 04:36, 20 July 2016 (UTC)

Correct convention in time?[edit]

at the upper right in a data box it says;

Orbital period 27.321661 d (27 d 7 h 43.19 min 11.5 s[1])

Shouldn't time that includes second not include fractions of a minute?

thanks. — Preceding unsigned comment added by Emkay4597 (talkcontribs) 09:23, 24 May 2016 (UTC)

Unknown permanent natural satellites[edit]

It is perfectly possible that unknown permanent satellites of Earth may exist. If they are small, no more than a few tens of metres across, and very distant, much further away than the Moon, they may well have escaped detection. I read recently, but can't find it right now, that such an object was found earlier this year, orbiting between about 30 and 100 times as far from Earth as the Moon. Its orbit is stable for at least a few centuries. I'll try to re-find the article.... DOwenWilliams (talk) 22:19, 16 June 2016 (UTC)

I haven't yet found the article I saw earlier, but I have found this one, which people here may find interesting.
http://www.bbc.com/earth/story/20160615-earth-probably-has-more-than-one-moon-a-lot-of-the-time
DOwenWilliams (talk) 22:35, 16 June 2016 (UTC)
Here it is.
https://groups.google.com/forum/#!topic/sci.space.news/_HIr90ZG28I
DOwenWilliams (talk) 03:25, 17 June 2016 (UTC)
2016 HO3 is not a natural satellite, but a quasi-satellite, a specific form of co-orbital configuration. The thing on bbc.com is about temporary natural satellites, not permanent ones. Hence, neither actually support including "known". --JorisvS (talk) 05:31, 17 June 2016 (UTC)
Prove to me that Earth has no permanent natural satellites besides the Moon. How are you certain that there are no rocks orbiting in the "Trojan" positions in the Moon's orbit, for example? Putting the word "known" in the article permits uncertainty. It allows that unknown satellites may, or may not, exist. Omitting the word asserts that no such satellites exist, which, in honesty, we cannot do. DOwenWilliams (talk) 20:49, 18 June 2016 (UTC)
Are they going to be stable, given how small they would have to be and taking into account all perturbations, including the effects of solar radiation? Either choice implies some knowledge about the state of our knowledge that we here cannot determine for ourselves, given that it is the Earth–Moon system itself, and would be otherwise be OR. The question we have to answer is: Is it possible for stable bodies (staying in orbit for hundreds of millions to billions of years) to have escaped detection until now? --JorisvS (talk) 19:41, 19 June 2016 (UTC)

Given that we are not in a position to give a definite answer to this question, we should put the word "known" in that sentence. Omitting it implies that we know the answer to the question. DOwenWilliams (talk) 04:23, 20 June 2016 (UTC)

The same problem exists with inserting "known": that means that there exists room for undiscovered stable moons, which we are not in a position to answer definitively either! Except with reliable sources, of course. --JorisvS (talk) 19:21, 20 June 2016 (UTC)
No, I don't see any parallelism here. Adding "known" is simply saying less; it doesn't need to be sourced. --Trovatore (talk) 19:29, 20 June 2016 (UTC)
No, it is not saying less. Saying "known" is done to indicate uncertainty in knowledge. We don't know if such uncertainty is justified here, just like we don't know if the certainty implied by leaving it out is justified. --JorisvS (talk) 20:26, 20 June 2016 (UTC)
Um, if "we don't know whether there is uncertainty", then there is uncertainty, ipso facto. --Trovatore (talk) 20:40, 20 June 2016 (UTC)
Yes, but where the uncertainty is is different. It's meta-uncertainty, uncertainty about the uncertainty, and the uncertainty is specifically ours, of us Wikipedians, not part of the collective knowledge of all humankind. --JorisvS (talk) 18:50, 21 June 2016 (UTC)

Are you certain, and if so how, that the collective knowledge pf humankind includes certainty about this? If so, you should be able to find something to cite, which in wikipedian terms, would settle the matter.DOwenWilliams (talk) 20:42, 21 June 2016 (UTC)

No, I'm not certain (how can I?). Even if there is no complete certainty, I can't imagine there isn't something quantitative about this out there. Your latter part is exactly where I wanted to get. I have some ideas about trying to dig something up, but any help would be welcome. --JorisvS (talk) 21:46, 21 June 2016 (UTC)
I know that searches have been done, using telescopes and radar, and no permanent natural satellites, other than the Moon, have been found. But of course this just puts an upper limit on the sizes of the satellites. It cannot exclude the existence of satellites smaller than the instruments could detect. Using more sensitive instruments might settle the question if any satellites are found, but if not the situation would be unchanged.
If there were some general thermodynamic calculation that could determine the long-term stability of the orbits of small satellites under the influence of sunlight, solar wind, etc., it might solve the problem, but I am not aware that any such calculation exists. The best that I have seen done is to simulate the motions of satellites over long periods of time, and see if they escape. But this approach has obvious limits.
For the purpose of this article, I think we should admit that there may be a theoretical possibility of the existence of permanent natural satellites of the Earth, other than the Moon. The fact that no such satellites are currently known means just that. The Moon is Earth's only known permanent natural satellite. That's what the article should say, no more, no less.
DOwenWilliams (talk) 03:09, 22 June 2016 (UTC)
I think JorisvS makes a good point about: Are they going to be stable, given how small they would have to be and taking into account all perturbations, including the effects of solar radiation? Even the Moon isn't completely stable nor permanent (though the Sun will go red giant before the Moon gets too much farther away from Earth). It seems painfully obvious, at least to me, that if any natural satellite of Earth were large enough to be (for all intents and purposes) permanent and stable, then it would already be "known" by now. "The Moon is Earth's only permanent natural satellite," is all this article needs. Anything more IMHO, such as the word "known", would tend to confuse general readers, which would not be an improvement to this encyclopedia.  Wikipedian Sign Language Paine  20:29, 29 June 2016 (UTC)
While I can see this both ways, I too wind up with JorisvS. Let's leave out the word "known." Jusdafax 20:39, 29 June 2016 (UTC)
This has been discussed before in archives 6 & 15. At one point, "known" was in the article and an editor called it a weasel word and asked that it be removed.  Wikipedian Sign Language Paine  21:00, 29 June 2016 (UTC)

Need for update according to https://en.wikipedia.org/wiki/Chang'e_4[edit]

https://en.wikipedia.org/wiki/Moon reads

"China intends to launch another rover mission (Chang'e 4) in 2015"

This should be updated to end of 2018 (instead for 2015) according to

https://en.wikipedia.org/wiki/Chang'e_4 — Preceding unsigned comment added by 2001:6B0:E:4B42:0:0:0:206 (talk) 20:18, 29 June 2016 (UTC)

Thank you for that, IP 2001+ – Good catch!  Wikipedian Sign Language Paine  20:46, 29 June 2016 (UTC)

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First sentence is weird[edit]

"The Moon is Earth's only permanent natural satellite, as well as the only celestial body besides Earth to have been visited by humans."

So humans have "visited" the Earth. Really? I think "besides Earth" should be removed. Tony (talk) 06:48, 21 September 2016 (UTC)

No, because the sentence without, "besides Earth," implies that there are no humans on Earth. Earth is a celestial body. Not reverting immediately, though, because I agree that the phrasing is clunky and humans did not "visit" Earth.  :) Can a better sentence be devised? LaughingVulcan Grok Page! 12:34, 21 September 2016 (UTC)
On second thought, the whole second half of that sentence was a fairly recent addition. The content is obvious (for now,) and (hopefully) a temporary condition. Why does it need to be there at all? LaughingVulcan Grok Page! 12:42, 21 September 2016 (UTC)
Thanks for the removal: works well. I have to dispute your proposition, though, that humans have "visited" the Earth. Have humans "visited" the UK, Beijing, NYC? Tony (talk) 05:43, 22 September 2016 (UTC) PS, you might consider using a slightly darker yellow for the first word in your signature; on my monitor it's not readable. Tony (talk) 05:44, 22 September 2016 (UTC)
Sorry, my own phrasing may have been clunky - don't know if we agree or not (and it probably doesn't matter either way.) I was saying that I agree that humans did not "visit" Earth. Though I suppose when I think about it, there well may have been a first human who set foot upon the UK, NYC, etc. Just not Earth, unless you buy into Douglas Adams' works as history.  :D Anyway, good call yourself on removing the initial fly in this particular ointment. LaughingVulcan Grok Page! 12:07, 22 September 2016 (UTC)