Talk:Lunar phase

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Irregular time between moon phases?

The article states that a complete moon phase cycle takes 29.53 days. But, according to the moon phase tables (for example): Between Full on Jan 14 09:48 UTC and Last Quarter on Jan 22 15:14 UTC there are 8 days, 5 hours and 26 minutes. However, between Full on June 11 18:03 UTC and Last quarter on June 18 14:08 UTC there are 6 days, 20 hours and 5 minutes. (calculated with [1]) Where does that difference come from? Is this due to libration? Is it consistent with a stated regular moon cycle of 29.53 days? -Tom-b 00:38, 15 May 2006 (UTC)

UPDATE: I just bought this answer at Google, feel free to add it to the article [2]

Lunar Fortnight?

Would be nice if somebody could define lunar fortnight such as used on the fasting page Togo 05:17, 20 May 2004 (UTC)

what lunar really means?

Southern Hemisphere difference in moon phases an error?

Is it true that "In the southern hemisphere, the above is reversed" regarding left and right sides of the moon? How could that possibly make a difference? -Unknown

I believe it is correct, because they are looking at it from a different viewpoint - they are "upside-down". While the moon seems to orbit in a counter-clockwise fashion when looked on from a point above the North Pole, it will appear to rotate in a clock-wise fashion when looked on from a point above (or below, however you want to think about it) the South pole. Also refer to: [3] -Unknown
What's it like when you're on the equator? I don't suppose you'd see the moon flip around when stepping from northern to southern hemisphere. Would you see the crescent lying on its back? Should this go into the article, perhaps with a picture? wr (talk) 11:39, 8 April 2009 (UTC)
At the equator, you would see the horns of the newish waxing crescent pointing upwards in the west soon after sunset, and the horns of the old waning crescent pointing upwards in the east soon before sunrise. AnonMoos (talk) 02:55, 10 April 2009 (UTC)
I believe this is incorrect - but only because it does not have anything to do with orientation (left to right) of the moon but perspective of the person. That is to say, if the moon is viewed rising over the horizon and the right half is a crescent - then this means that the crescent is on the southern side (i.e. the viewer is facing east and therefore right is south). The moon doesn't magically switch the "bright" side to the left (northern) side, when someone moves from viewing the mood rise from the northern hemisphere to the southern hemisphere. The only time that the crescent would "switch" from left to right is if the viewer was looking at a moon set instead of moon rise (and therefore right becomes north and left becomes south). I'm open to anyone explaining how viewing a rising moon from different hemispheres will somehow cause the moon to be "upside-down".--Pleitch (talk) 02:42, 16 April 2009 (UTC)
I understand that I'm wrong because of web sites like this: But I still don't understand why I am wrong. So I would be greatful if anyone can explain how a rising moon can have a southern side (right side) illuminatec when viewing from the northern hemisphere but the northern side (left side) illiminated from the southern hemisphere.--Pleitch (talk) 02:51, 16 April 2009 (UTC)
Imagine Superman standing at night in the northern hemisphere looking at a waxing half moon. It is nearly midnight and the half moon is about to set in the west. Its right and apparently northern half is lit. The line separating the lit and unlit halves is not perfectly vertical and the lit half is lower than the unlit half. This arises from the sun being far below the horizon. Superman begins to fly south. As he flies south, he and the ground below him rotate counter clockwise looking to the moon in the west and so the moon appears to rotate clockwise and lit half gets lower. Sometime when superman is in the tropics the lit half is directly below the unlit half and the line separating them is horizontal. As Superman continues flying south, the moon continues in its aparent clockwise rotation and so has its left side lit as is the case in the when he lands in the southern hemisphere. Finally, what is meant by the north side of the moon? To be latitude independent, it has to be the side of the moon that faces the celestial north pole (of Earth). At an equinox, exactly half this north side is lit at the waxing half moon and in the northern winter less than half this north side is lit. Karl (talk) 08:23, 16 April 2009 (UTC)

Accuracy of phase calculation?

I'm having trouble getting the lunar phase calculation at the bottom working. I think partly because of the terms it is written in. They seem cryptic to me. I also question the accuracy of the formula, as I found an alternative online and it was many times more complex. Perhaps this one will only work between such and such years? This is unclear, again as I said, as is the way to use the formula. For these reasons I suggest the formula be removed until someone more mathematically able than I has the time to fix it, or add more explanation for it's use. Weatherlawyer 21:35, 19 January 2006 (UTC)

The calculation does not take account of short term variations of the moon phase, which can put the calculated moon phase up to 15 hours out. Karl Palmen 09:30, 20 January 2006 (UTC)
It is horribly vague. Unless fraction() is a special function, or unless there are some missing parenthesis, I don't see how ".2 + x * .03" could ever yield anything anywhere near a new moon. (which would be 0) Can anyone clarify, or can I just angrily rip this equation out and vehemently shred it into figurative bits? --tyroney 18:39, 13 August 2006 (UTC)
The phase calculation appears to assume a circular orbit since it is a linear function. The fraction function is: frac(x)=x-int(x), that is always between zero and one. I have better a formula from a book Astronomical formulaee for calculators, 4th edition, 1988, by Jean Meeus. (Chapter 32). However it is much more complicated. ANYWAY, I've not tested the formula given here, and there's no apparent source reference (except link to author's website?), so I have no problem with removal. Tom Ruen 21:11, 13 August 2006 (UTC)
Actually, the correct definition of frac(x) is frac(x)=x-floor(x), that is, to yield the desired result of 0<=frac(x)<1, the truncation function must truncate downwards; floor(x) (if implemented correctly) always does this (e.g. floor(-3.5)=-4), but some implementations of int(x) truncate towards zero (e.g. int(-3.5)=-3).
I don't think an article about lunar phase is complete without some kind of calculation of lunar phase, probably with a note about possible inaccuracy (and after all, what degree of accuracy is acceptable depends on what use is going to be made of the information). Talking of accuracy, the length of the synodic month is given throughout the article as "29.53" days; surely this should be given to as close a value as possible? According to what I've read elsewhere, a much better value is 29.530588853 days. — (talk) 06:16, 16 September 2011 (UTC)
You have given the mean synodic month according to Meeus at J2000.0. Ignoring small higher order terms, it changes linearly by +0.0001337 days per century, which means that at J2012.0 it will have already changed to about 29.5306049 days. Individual synodic months vary greatly, from 29.275 days to 29.830 days, or about six hours less to seven hours more than the average. — Joe Kress (talk) 04:24, 17 September 2011 (UTC)

Contradiction with Eclipse

In the eclipse article, it is stated:

  • Lunar eclipses - the Earth obscures the Sun, from the Moon's point of view. The Moon moves through the shadow cast by the Earth. This can only happen at full moon.
  • Solar eclipses - the Moon occults the Sun, from the Earth's point of view. The Moon casts a shadow that touches the surface of the Earth. This can only happen at new moon.

However, in this article, the opposite appears to have been said:

"Note that the plane of the Moon's orbit around the Earth is tilted by about 5 degrees with respect to the Earth's orbit around the Sun. Therefore, eclipses of the Moon during the full Moon and of the Earth by a new Moon are rare and usually newsworthy."

I believe what is being said is that it's rare to happen during a perfectly full or new moon, but I don't know enough about the subject to tell which is correct--someone who does should make them match up. Chris 01:24, 13 May 2005 (UTC)

Clarified this somewhat. Johantheghost 09:48, 19 September 2005 (UTC)

Daylight Saving Time for table of Lunar phases' 2005-2020?

Seems to me that if UT is to be used for this table, daylight saving time should be ignored. I'd like to fix this - any agreement? -Unknown

Agree. There's also the issue that the daylight saving time rules have changed. Saros136 (talk) 05:22, 25 February 2009 (UTC)
I fixed it. Saros136 (talk) 11:21, 25 February 2009 (UTC)

Russian mnemonic

On 7 July 2005, added this statement to the Mnemonics section:

In Russian, the 'C' stands for "Стареющая" or "[a moon] becoming old", while a line is added to the waning crescent to form 'P', which stands for "Рождающаяся" or "[a moon] getting born"

That statement remained in the article until changed on 15 December 2005 by Flume to:

In Russia, the 'C' stands for "Стареющая" or "[a moon] becoming old", while a line is added to the waxing crescent to form 'P', which stands for "Рождающаяся" or "[a moon] getting born"

That edit changed waning to waxing. Can anyone cite an independent source supporting either the original statement or the change? --DannyZ 05:48, 16 December 2005 (UTC)

If I read the paragraph correctly, "[a moon] becoming old" means a waning moon, and "[a moon] getting born" would be the waxing moon, just coming out of the new moon state, therefore the phrase "while a line is added to the waning crescent to form 'P'" is wrong and correctly changed to waxing.
In my little russian knowledge, "Стареющая" means aging and "Рождающаяся" means emerging --RobiBuecheler 06:08, 10 February 2007 (UTC)

Expansion of Earth-shadow misunderstanding common to society

As illustrated in this comic: a lot of people are probably telling their kids the wrong thing, and believe it themselves. I actually realized that I had misunderstood the cause too! Tyciol 07:12, 26 May 2006 (UTC)

The link is not current. Koro Neil (talk) 06:08, 9 January 2009 (UTC)
live link --Belg4mit (talk) 20:43, 1 November 2010 (UTC)


I wonder why this page is a semi-regular target for vandalism? AnonMoos 00:53, 2 November 2006 (UTC) - ((Possibly because much of the writing is so atrocious?))Earrach (talk) 16:23, 10 August 2013 (UTC)

The following discussion is an archived debate of the proposal. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

Proposal: Merge New Moon and Full Moon with Lunar phase.

The result of the debate was do not merge. — Lunokhod 20:22, 28 November 2006 (UTC)

Merge comments

From a mistakenly created page Talk talk:Lunar phase, moved here by Fut.Perf. 22:15, 22 November 2006 (UTC):

TP: I am against merging Lunar phase with New moon and Full moon. Ages ago we split them because there is so much to say about the distinct phases and the page became too long. Tom Peters 16:38, 22 November 2006 (UTC)

FOR: I am for the move because

  1. the new moon page is very short.
  2. the full moon page is very short.
  3. lunar phase is short and needs editorial help and further additions in order to bring it up to "good article" status.
  4. the only important material that is not on lunar phases seems to be the formula.
  5. all three pages have some redundancy.

Lunokhod 18:19, 22 November 2006 (UTC)

I don't know that I have an opinion on the merge proposals, but I strongly disagree with you on the definition of the word "short"! I wouldn't call any of the three articles short, and I think that the article structure should be what will most clearly present the information (without worying whether any particular page meets the semi-arbitrary criteria for "Good Article" status")... AnonMoos 00:05, 23 November 2006 (UTC)

Against: It is patently false to call either the new moon, full moon, or lunar phase articles "very short" or "short". On the contrary, the proposed merge would make lunar phase too large and unwieldy. — Joe Kress 00:45, 23 November 2006 (UTC)

Proposed deletion of "Patent" section

I propose to delete the "Patent section." Perhaps someone can explain why this should be here? Lunokhod 11:07, 23 November 2006 (UTC)

TP: it is ... peculiar. I think it is potentially useful information; I suppose it could find a place under External Links. Tom Peters 11:31, 23 November 2006 (UTC)

Capitalization of New and Full Moon

Does anyone here know if "new moon" and "full moon" should be capitalized? Obviously "the Moon" is capitalized, and a generic "moon" is not. Perhaps both are acceptable? And if it is capitalized, is it "full Moon" or "Full Moon"? My guess is since these do not need to be preceded by "the" that they are not capitalized.Lunokhod 20:34, 28 November 2006 (UTC)

I don't know if they "should" be capitalized or not. I would be dismayed if there are rules that dictate such details. I always capitalize out of reverence for all the things upthere. Tom Peters 00:28, 29 November 2006 (UTC)
The Journal for the History of Astronomy specifically requires that when they are discussed as astronomical bodies they must be capitalized (Moon, Sun), but when their appearance in the sky is discussed they must not be capitalized (new moon, full moon, etc. JHA style sheet quote: "Sun, Moon, Earth if treated as astronomical bodies; sun, moon, earth if essentially appearances in the sky." — Joe Kress 07:03, 29 November 2006 (UTC)
(Tom, et al.: Perhaps we may, someday, see an end to formally approved sentences like "Jesus turned His face to the setting sun while behind Him He saw that the moon was already above the earth's eastern horizon."Earrach (talk) 17:00, 10 August 2013 (UTC)

Orientation of the Moon

I think that this page needs a section describing the "orientation" of the Moon, and how it depends on the day of the month and observation latitude. Does anyone want to take a stab at writing this? Lunokhod 09:57, 29 November 2006 (UTC)

I agree: apparently, the closer to the equator, the more the crescent resembles a smile (or, the U in the classic OUO "Diana" symbol) while the farther from the equator the more the crescent resembles a C or D. I have never quite been able to understand the geometry involved - naively, the Earth-Moon distance should totally overwhelm any observer-equator distance, and the angle of the crescent should depend only on the inclination of the lunar orbit. Apparently, this is not the case, and I'd like to understand why. (Yes, that's what brought me to this page.) --Jon Shemitz 01:53, 22 January 2007 (UTC)

I am totally ignorant on this but if someone could improve the part that explained the norther/southern hemisphere. being a continuum from -90 to + 90 deg, what does the "face" of the moon changes and what happens at the equator? --BBird (talk) 17:40, 9 December 2007 (UTC) found the answer at [4]. --BBird (talk) 15:53, 13 December 2007 (UTC)


Could someone explain to me, or clarify in the text, what this means?

"A first-quarter moon follows a daily path in the sky corresponding to that of the Sun after three months"

The rest of the paragraph is confusing as well. Lunokhod 23:31, 30 November 2006 (UTC)

If we neglect the 5° inclination of the Moon's orbit to the ecliptic and consider that there are three months in a quarter year, then the first quarter moon is at a position on the ecliptic that the Sun will be at three months later. At some point during each nychthemeron (night or day) the moon will cross the observer's meridian, when it reaches its greatest altitude above the horizon for that day. This will be above the southern horizon for northern hemisphere observers, and will be above the northern horizon for southern hemisphere observers. The ecliptic is inclined to the equator by about 23.5°, so regardless of the Sun's position on it, that daily altitude will cycle once each lunation from a high angle ("moon rides high") to a low angle ("moon runs low") and back again. The lunar phases when these angles occur depend on the month of the year, or, more specifically, they depend on the lunation in the tropical year. The paragraph only discusses the phases of the moon at the equinoxes and solstices. The terms "moon rides high" and "moon runs low" are each noted once a month on some day in the Old Farmer's Almanac. A Google search indicates that "moon rides high" is far more popular than "moons runs high", "moon rides low", or "moon runs low". — Joe Kress 02:55, 1 December 2006 (UTC)

Another question

Could someone explain the rational for doing this?

"If you photographed the Moon's phase every day for a month, starting in the evening at sunset, and repeating approximately 50 minutes later each successive day, you could create a composite image like the example calendar below from May 8, 2005 to June 6, 2005."

I am a bit confused as to how long the "month" is supposed to be here. I think the idea is to take a picture of the Moon every 1/30.5 days, but this is not too clear (to me). Lunokhod 23:42, 30 November 2006 (UTC)

A daily lunar photo will show the moon cycling through all lunar phases during each lunation. A synodic month lasts about 29.5 days, so each successive day the photo will have to be taken 1/29.5 days or 49 minutes later to equally distribute the phases. Each photo is 1.034 days later than the last. Although multiplying 1.034 × 29.5 does produce 30.5, that is the number of circuits the moon takes each lunation from the perspective of an observer on a rotating earth, one for each day plus one for the lunation. Remember the embarrasing SAT question (from the College Board's point of view) which asked how many times does a small circle rotate as it rolls once around a large circle (ratio of radii 1:3). The correct answer of 4 was not among the multiple choices! [5]Joe Kress 05:02, 1 December 2006 (UTC)
Joe, I think you are confused here. You can take a picture of the Moon as frequently as you want, and get a nice film as long as you do it regularly and cover the full synodic month. But every solar day the Moon has moved ahead, i.e. Eastward (counter-clockwise as seen on Northern hemisphere) w.r.t. the Sun. The (mean) Sun passes the meridian every 24 hours by definition. The Moon will pass the meridian 49 minutes later each day on average. So if you photograph the Moon repeatedly 1 day + 49 min apart during a lunation, you will capture it at about the same hour angle. However, as its declination varies by the full range during a month, the Moon will be at different positions in the sky and at different altitudes above the horizon. Also 1.034 days does not divide 29.5 so you would not take an integer number of pictures in a synodic month. In any case, the Moon does not make 30.5 circuits w.r.t. an observer on the surface of the Earth in 1 synodic month, and not even 29.5, but rather 28.5 . Tom Peters 12:12, 1 December 2006 (UTC)
The image caption for the phase calendar says that the images are taken 25 minutes later each day. Is this a mistake? Also could you explain where the 28.5 days comes from (and why it is not 29.5) and update the main article accordingly? This subject is obviously causing some confusion and needs to be clarified. Perhaps it would be worthwhile describing this in terms of lunar zenith to lunar zenith times (assuming the obliquity of the Earth and lunar orbit inclination were zero). A table of such times might prove useful. Lunokhod 14:14, 2 December 2006 (UTC)
Missed your comment, so late response. I suppose that the lunar phase calendar was generated as specified, i.e. 1d25m apart as stated. That makes sense. If you try to photograph the Moon every 24h it will be under the horizon in half of the cases. If you photograph it every 24h50m it will (approximately) in the meridian (or other specific hour angle) each time, but in half of the cases during day light so often invisible. If you take them 24h25m apart, starting from a new crescent Moon over the Western horizon just after sunset, then you'll catch a Full Moon around midnight in the meridian, and an old crescent Moon over the eastern horizon just before sunrise: i.e. you photograph at the most appropriate moments during the night only. On the 28.5: as stated, that is approximately the number of CIRCUITS that the Moon makes w.r.t. an observer on the surface of the Earth during the 29.5 DAYS that a lunation takes. In any case it is not 30.5 as Joe Kress stated. The Moon takes longer than a day between merdian passages, not shorter. Tom Peters 12:34, 14 December 2006 (UTC)

Where is the picture that is mentioned in the calendar section text?--mikeu (talk) 22:58, 13 December 2007 (UTC)

{{== The First Picture ==

What exactly is the first picture supposed to be? It shows the moon with the words '2nd quarter' and the value '72%' below it. According to the lunar phase chart on here, we're between the first quarter and full moon, so the picture doesn't represent the current moon phase. What is its purpose?--Jcvamp 16:29, 30 December 2006 (UTC)

Actually, the Moon did reach the 72% illumination mark yesterday, so it's not that far off. What I don't like is that it uses "2nd quarter" to mean something different than it does in the article, apparently meaning between 50 and 100% lit. Saros136 16:59, 30 December 2006 (UTC)

The thing that threw me off was that it says '2nd quarter' when it fact it's between the first quarter and the full moon. It's the text describing that moon as '2nd quarter' that needs to be changed.--Jcvamp 08:48, 31 December 2006 (UTC)

That's called a "gibbous Moon" (which may be waxing or waning). There is no such thing as a "2nd quarter". There are first and last quarters, and a Full Moon in between. Tom Peters 14:39, 31 December 2006 (UTC)
I know it's called a gibbous, (in fact it's a waxing gibbous at the moment) but I was discussing the phase in terms of quarters as it mentions the phase as the '2nd quarter' on the page. I also know that it isn't usually called the second quarter, but that's what it says erroneously (which is the point I'm making here) on the page.--Jcvamp 14:20, 1 January 2007 (UTC)
So complain at User:Dbachmann who provides the Wikiprogram that draws this.—Preceding unsigned comment added by Tom Peters (talkcontribs) 18:07, 1 January 2007

Is the picture the same whereever you are in the world, surely the moon looks difrent depending on your latitude ? —Preceding unsigned comment added by (talkcontribs)

No, it is affected by horizontal parallax (also, besides your latitude, depends on your longitude and the time): it is about 1 deg., so not noticeable at the scale of the picture. Tom Peters 16:27, 24 January 2007 (UTC)

Hi Tom

If I understand correctly you are from South Africa and thus Southern Hemisphere?

My mentor and I have been thinking about the same scenario for the past 7 days and we have come to a realization. If you are viewing the phases from the Northern Hemisphere I would be like you see in every Picture on the Internet about Moon Phases.

However: Being in the Southern Hemisphere, we should see the Mirror image of this (Actually upside down...)

I will include a picture of how we think it should be: As seen from the Northern Hemisphere...

Louis Willemse and Riek Basson, Afritracks cc South Africa

Kind regards and Happy Stargazing! —Preceding unsigned comment added by (talk) 18:45, 19 March 2011 (UTC)

Southern Hemisphere Moon Phases

Proposed deletion of Lunar phase equation

I do not find the equation that predicts the lunar phase as a function of time useful, and propose it for deletion. In particular, it would be much easier to go to any of the numerous online lunar phase calculators to determine this, than to determine how many days have passed since 12AM, January 1, 2001 (Greenwich time). Perhaps we should just give a reference on where to find this equation for those of us who might want to calculate this quantity. Lunokhod 20:53, 30 December 2006 (UTC)

You seem to really hate numbers (considering your similar proposals in New moon, Full moon, and Full moon cycle. You are correct that there are many places on-line where one can find the current phase of the Moon. There are several links in the References section. However, I don't see why such information should not also be included in the Wikipedia, which as an encyclopedia is a collection of knowledge taken from elsewhere. However I don't know of on-line resources that explain HOW to computate such results. This may be useful to check phases in the past or future. This particular formula appears to be taken from an almanac. Tom Peters 14:47, 31 December 2006 (UTC)
For the record, I'm a theoretical geophysicist, so I have nothing against equations! My concern with this one is the following: Only a very small percentage of people who read this page will ever want to calculate the lunar phase as a function of time. Of those specialists that would like to do this calculation, they will probably find this equation to be inadequate: I doubt that that the number of decimal places quoted is justified, and it is clear that this equation neglects the eccentricity of the lunar orbit. How one deals with changing time zones is not described, nor is the range of dates for which this equation is accurate. Furthermore, though not a criticism of the equation itself, a non-expert or expert could easily make an error concerning leap years, or mistakenly use year 2000 (which is the standard epoch for orbital calculations) instead of 2001, which is used in this formula. Lunokhod 16:31, 31 December 2006 (UTC)
OK, I would agree that the expression should use a standard epoch, be referenced, and have some caveats. But I dispute the notion of "little interest"; such simplified expressions are routinely given in almanacs. Wikipedia does not have the limits of a paper encyclopedia so I see no reason to not serve all audiences. Also such computational details seem not to be readily available elsewhere on-line, and I think it is completely within the purpose of Wikipedia to make such things available on-line. Tom Peters 09:57, 1 January 2007 (UTC)
It gives mean lunar phase (i.e. using a constant angular velocity) as a function of GMT or UTC or whatever the latest acronym is. An accurate equation for the moon's non-averaged position would take up multiple pages (it did take up multiple pages in the book that Laplace (I think it was) devoted to deriving it). AnonMoos 00:10, 1 January 2007 (UTC)
Yup, and an (obsolete) reference to Meeus to compute more precise phases follows. Do you have anything more specific on who derived which equations? The earliest I know are from Hansen (Leipzig 1858, 1863). Tom Peters 09:57, 1 January 2007 (UTC)
Could someone please at least add a reference to the equation in question so that I can verify it (the equation just changed by 12 hours if I understand the last edit correctly!)? Otherwise, in accordance with Wikipedia policy, I will delete it irregardless of the community's concensus on whether it is useful or not. Lunokhod 11:02, 1 January 2007 (UTC)
Ooops, sorry for not discussing it. 12 AM seemed ambiguous; I've seen it refer to midnight and noon. I thouhgt 0 ut was intended because it gave a better match to some dates of phases I tried. I'm not sure I was right, though-it might depend on the years. For 2001, 0 UT would have given a closer match at the times of full moons, 10 of 12 times, 9 of 12 1st quarters, 6 of 11 3rd qtrs, and it's a tie on new moons. I haven't done all of 2007, but the 0 UT base is better for new and full moons.—Preceding unsigned comment added by Saros136 (talkcontribs) 12:38, 1 January 2007
Similar equations were in all the annual Naval Observatory almanacs (though I haven't seen one in a while), and I assume somone changed it from a noon to midnight epoch (or vice versa) -- it doesn't really matter which one is used, as long as it's made clear. AnonMoos 12:41, 1 January 2007 (UTC)

The equation in question was added on 11 March 2005 by Monsieur le docteur Ralph without any attribution as follows:

where t=[UT]-[12AM, January 1, 2001], days
such that new moon=.0, first quarter=.25, full moon=.5, last quarter=.75

The equation is approximately correct for midnight. An equation close to that by Ralph can be obtained as follows:

JDE = 2451550.09765 + 29.530588853k + 0.000 1337T² − 0.000 000 150T³ + 0.000 000 000 73T4
where JDE is the Julian Ephemeris Date of the mean phase of the moon, k is the number of mean synodic months (including any fraction thereof) since the first mean new moon after J2000.0 (2000 January 6), and T is the number of Julian centuries since J2000.0. From Jean Meeus, Astronomical Algorithms, p.319. Meeus' warning that any value of k other than 0, 0.25, 0.50, or 0.75 is meaningless only applies if the equation is used to calculate the true phase of the moon.
1/29.530588853 = 0.03386319199
Julian Date of 2001 January 1 00:00 = 2451910.5
k = (2451910.5 − 2451550.09765)/29.530588853 = 12.204374
0.20439731 − 0.204374 = 0.00002331 ≈ 2 seconds

Because ΔT = TT − UT = 64.09s at 2001.0, a 2 second error implies that the time should be TT, not UT. The phase calculated via the following equation (with the given precision) is accurate to ±0.004 after three millennia when the small terms in T are ignored.

phase = (0.2044 + t×0.033 863 182) mod 1
where t is the number of days since 2001 January 1 00:00 TT, 0 ≤ phase < 1

Joe Kress 06:23, 5 January 2007 (UTC)

I wish to draw to your attention the following enhancements:

if phase<0. then phase=phase+1.; /*OK for any date*/
linear= 4.*abs(phase-.5)-1.; /* -1<=effect<=1 */
moreal= cos(6.283185307179586476925286766558*phase); /* 2*pi*phase */

-Trift (talk) 16:10, 22 April 2011 (UTC)

Current phase template

Could that be moved into standard template space? 22:14, 18 April 2007 (UTC)

Several Comments

I've noticed a couple of things that could be corrected or changed with this page. First, the diagram under "Names of lunar phases" does not distinguish from which direction the sunlight is coming. In fact, the bottom of the picture looks brighter, insinuating that the sun is downward, which it is not. The direction to the sun should be added. In the chart just below that, there are no differences between the Northern Hemisphere column and the Southern Hemisphere column so why put two columns? The statement, "When the Sun and Moon are aligned on the same side of the Earth, the Moon is "new", and is not illuminated by the Sun" is wrong. The visible side of the moon is not illuminated, but half of the moon is always illuminated by the sun. 04:19, 29 October 2007 (UTC)

Red luna

Around the 21st of October 2007, i awoke to see luna had turned an orange colour. (note: IT WAS NOT SOL!) Anyone know what it is?OsirisV 21:29, 30 October 2007 (UTC)

1. We typically call Luna "the moon", at least where I live 2. We typically call Sol "the Sun", at least where I live 3. Dust in the atmosphere casues the moon to appear different colors. 4. Your post was a joke, right??? —Preceding unsigned comment added by (talk) 15:45, 26 February 2008 (UTC)

This can also be the time of a lunar eclipse. The Moon can turn into the colours of red and orange at this time. (I think Sol=solar eclipse.)Chimchar monferno (talk) 08:39, 20 March 2008 (UTC)
It couldn't have been a lunar eclipse, since those happen only at full moon (when the moon is about 15 days old). On 21 October 2007, the moon was 10 days old. — (talk) 06:27, 16 September 2011 (UTC)

Picture of Lunation

Prior to creating this section, Cm had submitted a contrib, a few minutes earlier in two edits separated by 29 seconds, then removed it at 8:40, and then at 8:42 submitted (in the preceding section, "Several Comments") the related text that follows, and which i now both restore in this different location and strike thru -- each to reduce confusion under various circumstances):

:( This should help, although it's rather a bit smugy.Chimchar monferno (talk) 08:37, 20 March 2008 (UTC)

In case if you didn't know, the phases of the Moon are called the lunation. I uploaded a picture because everyone was asking for one. Sorry if the picture is incorrect or smugy. If anyone wants, put this image in the article. ( —Preceding unsigned comment added by Chimchar monferno (talkcontribs) 08:42, 20 March 2008 (UTC)

Let's say, Let's add to lunar phase anywhere.You decide.
-- (talk) 20:12, 12 September 2008 (UTC)
A possible misunderstanding exists here. The sequence in time of all lunar phases from new moon through first quarter, full moon, last quarter and back to new moon constitute a lunation. A lunation is a period of time that lasts about 29.53 days. A collection of the phases themselves whithout any mention of time is not a lunation. The cited image is incomplete because it does not mention the period of time. — Joe Kress (talk) 03:56, 13 September 2008 (UTC)

Missing picture

In the 'Calendar" section, this text appears" If you photographed the Moon's phase every day for a month, starting in the evening after sunset, and repeating approximately 25 minutes later each successive day, ending in the morning before sunrise, you could create a composite image like the example calendar below from May 8, 2005 to June 6, 2005.. But the corresponding picture "below" seems to be missing. Either the picture should be put back, or the text deleted. Geoffrey.landis (talk) 13:48, 22 September 2008 (UTC)

(Dfoofnik) : the sequence is still missing as of March 9, 2009. I was wondering if the text was misleading, since it says there is one day with neither moonrise nor moonset (there should always be one or the other or both) this referencing the "invisibility" of the New Moon??

No, see, the Earth rotates in 24 hours, but the Moon takes 24 hours plus about 25 minutes to revolve around the Earth, so if the Moon rises just before midnight one night, it will rise after midnight the next night and "skip" a day on the calendar. The article misleads us into thinking the rising and setting can both skip the same calendar day but (unless I am mistaken) this is impossible. I'll go reword that sentence now.

    • However it seems that the text that corresponds to this photo (month calendar) is missing information. There is no statement of the location on Earth from which the photo would be taken, and also no reference to which time format is being used (GMT, GMT+1, EST, EDT, etc., since we start our sunset calculations on May 8). Regarding when the photo is taken, the term "after sunset" is imprecise. Does it mean to take a photo exactly at sunset? Or exactly how long 'after' sunset? All of this makes a difference in the results. As far as I can see this is crucial to exactly which calendar day would contain the missing lunar phase. If you use Greenwich England as your location and GMT as your time format, and you start taking your photo on the day of the New Moon, exactly at sunset (it will not be that dark, so you will not get a great photo) on May 8, 2005 at 19:35 (using data from ), and proceed as instructed, then the day missing would be May 19, not May 20. If you use the locaton NYC (EST) then its May 18 that has the missing phase in the calendar. Daylight Savings Time for any location produces a result a few days earlier, in fact moving the time up to a certain amount of minutes after sunset will only result in an earlier calendar date for the missing lunar phase. There definitely needs to be more information listed, as there are a lot of assumptions, unless I'm missing something. Mbase1235 (talk) 21:43, 1 January 2010 (UTC)

Two 100% issues

The two following msgs were placed on ToDo; i reduced the entries there to a ref to this sectn, since the tasks are so ill-defined that they require discussion before action.
Jerzyt 09:20, 1 December 2008 (UTC)

  • New moon
    • The new moon is not invisible as stated in the first paragraph. It is very visible and looks like a full moon during the day. Please fix this.
      (by Template:Ipuser at 19:45, 14 September 2007 )
      Transferred to talk by Jerzyt 09:20, 1 December 2008 (UTC)
      • "[L]ike a full moon during the day" sounds to me like an attempt to say that the new-moon geometry has the nearside facing the daytime side of the earth, and tho lacking direct illumination from the sun, the planetshine from reflection illuminates it by reflection, much as the eclipsed moon is illuminated. OK, but it's always at the noon meridian, and i'm grossly skeptical of its being naked-eye detectable, even near dawn or dusk, since it has to be within ... what, 5.1° of the sun?
        --Jerzyt 09:20, 1 December 2008 (UTC)
  • Full moon
    • the moon is never 100 percent visible as is stated in the article. Even during a full moon, there is a slight sliver missing. the only time that it could be 100 persent lighted is during the peak of total eclipse.
      (by Template:Ipuser at 00:06, 16 June 2008)
      Transferred to talk by Jerzyt 09:20, 1 December 2008 (UTC)
      • We say the "portion of the illuminated hemisphere that is visible to an observer [is] 100% [at] full moon", but a stationary observer has a small band by the terminator hidden from them by nearer points on the moon's surface: the two most widely separated lines drawn from my eye to points where they are tangent to the moon's surface are 400K km long and their tangent points are separated by 3.5K km, so i think the width of the roughly cylindrical portion of the surface that's in the near hemisphere but over my lunar horizon has to be about 1% the moon's circumference; is that what we're talking about? Someone should do that geometry, and we can say "all but 1%" or whatever that works out to.
        Actually, the sun illuminates a bit more than a hemisphere (similar geometry problem), bcz its diameter is larger than the moon's, and it "peeks around the corners" a little.
        Huh? Why is an eclipse mentioned??
        --Jerzyt 09:20, 1 December 2008 (UTC)

Rated as B class?

How can this article possibly be rated a B class when it fails the first of the necessary criteria? Which is:

"The article is suitably referenced, with inline citations where necessary. It has reliable sources, and any important or controversial material which is likely to be challenged is cited. The use of citation templates such as {{cite web}} is not required, but the use of <ref></ref> tags is encouraged"

Richerman (talk) 20:51, 27 December 2008 (UTC)

Northern / southern views

A waxing crescent moon if viewed in the northern hemisphere or a waning crescent moon if viewed in the southern hemisphere.

This caption is not strictly accurate. The orientations for the two hemispheres are reversed, but the visible features of the moon at any time are the same for both hemispheres. The photograph needs to be replaced by the image of a plain crescent shape without features, or by two photos with the same shape but different features. Koro Neil (talk) 06:24, 9 January 2009 (UTC)

Worse than that confusion, the photo is a mirror image! Tom Ruen (talk) 17:23, 9 January 2009 (UTC)
:) Koro Neil (talk) 09:21, 13 January 2009 (UTC)
The article as a whole is somewhat lacking in the southern-hemisphere perspective. There is a table, but no other detail. All of the diagrams and illustrations are for the northern hemisphere only. It would clarify this article greatly if some diligence was shown for the southern-hemisphere perspective. -- B.D.Mills  (T, C) 05:02, 23 February 2009 (UTC)


dear wiki,

For security, I'm obliged remove that Ay.gif.That's because of itü.sözlük. article.thanks.-- (talk) 19:23, 25 February 2009 (UTC)

Are you trying to say that it infringes copyright? Sillyfolkboy (talk) 23:02, 25 February 2009 (UTC)

I has been deleted Ay .gif.because,I don't want stand there.I am not child.I'm Adult.+26. please,you behave as a are not child.This is make very easy animations.that is, kidlike.for him, (talk) 10:21, 10 June 2009 (UTC)

Deletion reverted, given that the licence appears to be in order. If there are details that we should be aware of, please let us know. --Ckatzchatspy 10:37, 10 June 2009 (UTC)

ok,your message is forwarded.What I do?no need details.All delete now.-- (talk) 12:17, 10 June 2009 (UTC)

will be Ay.gif file .I don't think upload again.goodbye.-- (talk) 12:22, 10 June 2009 (UTC)

Are you silly?pal,Don't put there.I say,delete file Ay.gif.I can't understand that.I still and still.İf you have a question,I would answer.-- (talk) 13:25, 10 June 2009 (UTC)

you can't edit belong something can't promote name ---------.please delete.look Ay.gif as can delete All will be had delete.ok.-- (talk) 13:37, 10 June 2009 (UTC)

I'm afraid,no licence information.Will be happen?-- (talk) 13:47, 10 June 2009 (UTC)

Please do not remove the link without a clear, distinct explanation of why you feel this is necessary. If you are unable to clearly communicate in English, please ask for assistance. I notice that you also attempted to remove the valid licence information from the Commons image, again without explanation. This is unacceptable; we are happy to assist, but there must be a clear and verifiable discussion process. Repeatedly attempting to delete the image does not assist in said process. --Ckatzchatspy 17:01, 10 June 2009 (UTC)

I'm warning you.delete quick!I don't want it there,sir.Don't shake your honour,sir.-- (talk) 20:24, 13 June 2009 (UTC)

Did you create the image yourself? And do you have proof of it? Is the image a copyright infringement (Telif hakkı)? Sillyfolkboy (talk) (edits)WIKIPROJECT ATHLETICS NEEDS YOU! 23:30, 13 June 2009 (UTC)

yes,I did create.I have proof of,no copyright.licensing section,I have selected in such manner.-- (talk) 08:27, 14 June 2009 (UTC)

good you are,I did explain. delete waiting..-- (talk) 08:51, 14 June 2009 (UTC)

Moon visible almost all month?

Hangon, the image here shows the moon rotating the Earth. That can't be true, if the moon is actually visible almost all month long. Surely there are weeks when the moon is on the wrong side of the earth? A darkened moon is still faintly visible for the great majority of the month. I'm really really confused by this, and I don't think the article explains it at all. The moon rotates around the earth's axis, right? Mostlyharmless (talk) 03:08, 2 December 2009 (UTC)

The Moon revolves around the Earth-Moon center of mass, which is within the Earth and hence not too far from Earth's axis. The Moon is visible from everywhere on Earth (except one or both polar regions) sometime during every day of the month (not all day), except for two or three days around astronomical new moon, when the Moon is between the Earth and Sun. At that time the side of the Moon facing Earth is not illuminated by the Sun so no portion of the Moon can be seen. However, if it is two days after new moon, then a thin crescent moon becomes visible for a short time (less than one hour) just above the western horizon shortly after sunset, before the Moon itself sets. Similarly, if the Moon is two days before new moon, a thin crescent moon is visible for less than an hour just above the eastern horizon shortly before sunrise, before the sun rises and its excessive sunlight drowns out the moonlight. These crescents are visible from most places on Earth in both the tropics and the temperate zones of Earth, at about the same local time. As the angular distance of the Moon from the Sun increases, either before or after new moon, then the moon is visible longer each day until full moon, when the Earth is between the Moon and Sun, when the moon is visible all night long, from sunset to sunrise (moonrise to moonset). — Joe Kress (talk) 04:53, 2 December 2009 (UTC)
I know all that... but I still can't see how that explains how you can see the moon when it's on the other side of the earth. Mostlyharmless (talk) 06:24, 2 December 2009 (UTC)
Short answer, you can see the moon everyday (minus new moon; or living north of the Arctic Circle / south of the Antarctic Circle), by waiting for it to rise. It is no different then waiting for Sun to rise everyday. The Earth completes a rotation once every 24 hours. -- Kheider (talk) 16:28, 2 December 2009 (UTC)

File:Lunar libration with phase Oct 2007.gif to appear as POTD soon

Hello! This is a note to let the editors of this article know that File:Lunar libration with phase Oct 2007.gif will be appearing as picture of the day on June 18, 2010. You can view and edit the POTD blurb at Template:POTD/2010-06-18. If this article needs any attention or maintenance, it would be preferable if that could be done before its appearance on the Main Page so Wikipedia doesn't look bad. :) Thanks! howcheng {chat} 19:04, 14 June 2010 (UTC)


Week came from the Lunar phase. New Moon, First Quarter, Full Moon and Last Quarter: There are nearly 7 days between them! Böri (talk) 11:41, 8 June 2011 (UTC)

Alternate formula

See New_moon#Determining_new_moons:_an_approximate_formula. -Trift (talk) 18:26, 24 June 2011 (UTC)

See also

for See also list?- Specular highlight ? Limn? SignedJohnsonL623 (talk) 03:55, 9 October 2012 (UTC)

Use of images

One issue which does confuse a lot of beginners in astronomy (namely late primary school / early high school science) is that all the images are flat and gives the impression that we should not be able to see a full moon at all (because in the image it lies directly behind the earth and so sunlight shouldn't reach it. I think you should uses better images which correct for this and makes quite clear the tilt in the moon's orbit as to how most of the time it is above or below the earth's orbital plane. — Preceding unsigned comment added by (talk) 17:14, 1 June 2013 (UTC)

- - Virtually all attempts at making fixed diagrams explaining the cause and sequence of the Moon's phases fail. They fail because the illustrators feel they have to portray two very different conceptual arrays at the same time, in the same diagram, usually even with one array superimposed upon the other. This can be avoided in animated displays or videos allowing one to pan the view through three dimensions over time but is a very hard thing to solve in a static diagram. Not only does the basic layout showing the moon's orbital positions relative to the sunlight "not get along" cognitively with the typically adjacent icons of how the Moon looks in the sky at that moment in its orbit but, as you note above, in the alternate tilted 3/4 view perspective versions the point-of-view of the observer always precludes the clear portrayal of at least one important lunar phase. Earrach (talk) 16:46, 10 August 2013 (UTC)