Talk:Lunar phase

First and last quarter

I think the moon is exactly half when the earth and sun are 90° apart from the moon, not when moon and sun are 90° apart from the earth. And the reason is that for the moon to be exactly half, the sun would have to be shining directly on the edge of the visible part of the moon, meaning that the sun and earth would have to be 90° from the moon. Which means about 89.857° from the earth if the sun is 400X farther than the moon. The Channel of Random (talk) 16:32, 14 January 2020 (UTC)

You are correct. And there seems to be several other places where the terms are mixed up in this article.

The moon is at dichotomy (half-lit) when it has swung 89.85° through it's orbit around Earth, NOT 90°.

About 6 hours after the moon is exactly half lit, when it's more than half lit (50.1%?), THEN it becomes a quarter moon, when at quadrature (90°). I think...

This article seems to say exactly that... right before contradicting itself and saying the opposite.

But all the sources I've found online are sloppy and woefully conflate "Quadrature_(astronomy)" with "dichotomy" with "quarter moon" (even NASA!!!) so I'm not sure what the definition of a quarter moon is, nor even if there is a scientific definition for a quarter moon, versus just a sloppy, common term for any time when it is around 89ish or 90ish degrees until 134ish or 136ish degrees +/-. Skintigh (talk) 23:06, 9 December 2022 (UTC)

The official and traditional astronomical definition is given in the first footnote. Why would you want to define the lunar phases as seen from the Moon as most people actually live on the Earth? I agree that the article should clearly distinguish between the quarter phases and dichotomy. AstroLynx (talk) 12:14, 10 December 2022 (UTC)

External links

The external links on this article have been tagged as of concern for some time, and listed at Category:Wikipedia external links cleanup. They appear not to meet the requirements at Wikipedia:External links, failing WP:ELNO#1 at least. However, they may be of use to editors wishing to work on the article, so they have been moved here. If, after examination, a link is found not to be useful it can be removed from this list. If the link does prove useful and it meets the WP:RELIABLE criteria, appropriate information can be summarised in the article, using the link as an inline citation, and then the link can be removed from this list. Some links may be appropriate to be used as external links per EL criteria; however, be aware that, per WP:ELBURDEN, none of these links should be returned to the article without first discussing it here and gaining consensus. SilkTork (talk) 18:36, 8 July 2021 (UTC)

Art and Culture

• This page is linked by a few articles that use the crescent moon as a symbol, and it would benefit from some discussion about the prominent symbolic uses of a crescent moon Immcarle183 (talk) 07:17, 9 March 2022 (UTC)

General

• Six Millennium Catalog of Phases of the Moon
• U.S. Naval Service on Moon Phase / What the Moon Looks Like Today (United States Naval Observatory)
• Moon Phase For Any Date (Full moon date analysis from 1900 - 2050)
• Full Moon Names
• Current Moon Calendar
• The Length of the Lunar Cycle (numerical integration analysis)

Educational aids

• Open Source Physics Lunar Phase Model
• Lunar phase simulator (animation)
• Starchild: Moonlight Madness Lunar Phases Game
• Names and Images of the 8 moon phases
• Astrophysics Science Project Integrating Research & Education: Lunar Phases Quiz
• Lunar Phase Image Sets In High-Resolution (1200x1200 pixels) at 1-Degree Intervals - Views of the Moon From 4 Sides at Any Relative Phase
• Front/Back/East/West Lunar Phase Explorers
• Mnemonic devices for the Lunar phases
• Moon activity idea from Jet Propulsion Laboratory

— Preceding unsigned comment added by Aicraftor (talk • contribs) 17:40, 28 August 2023 (UTC)

Calendar

The section "Calendar" should be about the use by humanity of the lunar phases as a form of calendar. Instead it takes three paragraphs to explain that lunar months and Gregorian calendar months have different lengths and so are not in phase. Shock - not.

So two questions for debate:

1. does the section as it stands have any value? If so, it needs a different section name.
2. A section about calendrical use of lunar phases should actually say something about the subject. Would it be enough to just copy the lead of lunar calendar or do we need something a bit longer that also describes lunisolar calendars too. And maybe even Blue Moons.

𝕁𝕄𝔽 (talk) 08:41, 29 August 2023 (UTC)

I don't think the section is important enough to keep.

Some sort of section, even shorter than the lunar calendar lead, with a "Main article" template, would be appropriate.

When I saw mention of lunar phases and the Gregorian calendar, I thought of the aspects of the Gregorian calendar that are used to calculate the date of Easter. But that is exhaustively covered in other articles, and I don't think it needs to be mentioned here.Jc3s5h (talk) 16:41, 29 August 2023 (UTC)

I have deleted the section about lunar and calendar month coincidences. Consensus is that it had no value. I have added a brief section on use of lunar phases for "timekeeping" (long-range time, as in "four moons ago" rather than "four minutes ago").--𝕁𝕄𝔽 (talk) 16:03, 3 September 2023 (UTC)

Almost repetition

The two initial files in the article are almost the same. – Hamid Hassani (talk) 08:00, 3 September 2023 (UTC)

They're not the same at all. The first one shows the lunar phases and librations as viewed from the Northern Hemisphere and the second one from the Southern Hemisphere. – Hamid Hassani (talk) 02:39, 17 September 2023 (UTC)

Distinction between common vernacular "lunar phase" and astronomical "lunar phase"?

I was recently educated re: the distinction between "lunar phase" as commonly understood: the percentage illumination of the lunar disc, and as it is apparently considered in astronomical context: defined by the alignment of the sun/moon/earth system as viewed from the perspective of the ecliptic. E.g. today there was an eclipse of the sun, which peaked at 9:20am from my location, which intuitively must be the new moon since the moon face is never less illuminated than when the sun is directly behind it, but the official "new moon" time was 10:55am, because that was when the moon was directly between the sun and earth from the perspective of the ecliptic plane. It seems like this distinction should be made in this article, and I would add a section but I don't feel qualified to do so. Any takers? Chconnor (talk) 00:36, 15 October 2023 (UTC)

Hat note

I appear to have upset user:AukusRuckus by questioning their decision to move the {{confusing}} hatnote from a single arguably confusing section to the top of the article.

IMO, the effect of that note at the top of the article is to assert that the whole article is confusing. That, at least to me, seems a significant overreaction, because it is not a reasonable assessment of the article as a whole. (I accept to call it "extreme" was, well, extreme and I withdraw that adjective but the rest of my challenge stands.)

Before applying such a full-on mark of condemnation to an article, I would expect to see a talk page topic that makes the case that the whole article is a hopeless case, completely incomprehensible, beyond repair. I see no such case. If the state of the article is anything less than that severe, then the tag is an overreaction.

In the final analysis, WP:so fix it applies unless you really don't have any idea what it is trying to communicate. 𝕁𝕄𝔽 (talk) 16:42, 29 October 2023 (UTC)

I didn't apply it, though — someone else did. So "WP:so fix it" in no way applies to my edit, but the original tagger's. (And if you took your own advice, you'd have "just fixed it" by simply removing he offending hatnote.) There is a talk page discussion on it, above, in fact. I just followed what I thought had been intended (we don't put banners in the middle of text. Such locations require an inline tag).

What I objected to was the wholly unnecessary reversion: Just remove the hatnote. You undid the DAB link fix for no good reason, one that I had mentioned, front-and-centre, in my ES. There was no need to just undo everything willy-nilly.

I take your point about it being obtrusive (but you should try stumbling around and finding a huge block like it in the notes section, when you can't see well) for a relatively small problem: So just remove that and nothing else. Only revert as a last resort, especially if you're not willing to look at what else you're reverting.

(So, do you realise I was not the editor who put the tag into the article? From your comment, it seems you think I was ... Could you look at the diffs please? I can see how I may appear ott to you, but my edits—which I really enjoy doing—are rather more effortful than the average person's, I imagine, due to a visual disability: So I can get in a bit of a tizz when they're undone off-handedly.

In the final analysis, this kind of reversion is just discourteous. Nevermind, expect it'll all come out in the wash. AukusRuckus (talk) 17:14, 29 October 2023 (UTC)

but am I right in saying that it was your edit that moved the "confusing" tag from the section to the whole article? I'm editing on mobile at present and am aware how its limitations can generate misunderstandings. I hope that this is not another such.

I recognise your edit was made in good faith and if we should cross paths again I will aim to ask questions first and shoot afterwards. 𝕁𝕄𝔽 (talk) 19:05, 29 October 2023 (UTC)

Date format

The date format of the article has been inconsistent. A recent edit by Jitro160599 (talk · contribs) changed a few dates from the mdy format to the dmy format. The earliest version of the article I found that has dates, from January 2006, uses the mdy format. The earliest version I found that has citations with dates uses a style that is no longer accepted, yyyy-mm-dd for publication dates. I suggest the format for dates outside citations be restored to mdy, and the mdy format be used within citations as well. Jc3s5h (talk) 17:02, 18 December 2023 (UTC) lllllllllllllllllllllllllll

What about history?

I came to this page hoping to find some imformation about early theories to explain the phenomenon. I do not know why this is completely omitted. Anyone knowledgable in the subject, please create a section, hopefully it will be expanded overtime. DivinePtr (talk) 13:50, 17 April 2024 (UTC)

Moonphase highest and lowest in the sky

New Moon - highest on summer solstice and lowest on winter solstice.
Waxing Crescent Moon - highest in astronomical spring and lowest in astronomical autumn.
First Quarter Moon - highest on vernal equinox and lowest on autumnal equinox.
Waxing Gibbous Moon - highest in astronomical winter and lowest in astronomical summer.
Full Moon - highest on winter solstice and lowest on summer solstice.
Waning Gibbous Moon - highest in astronomical autumn and lowest in astronomical spring.
Last Quarter Moon - highest on autumnal equinox and lowest on vernal equinox.
Waning Crescent Moon - highest in astronomical summer and lowest in astronomical winter.

This is what I found when the moonphases are at it's highest and lowest. 2603:6011:E00:4C41:0:0:0:100A (talk) 16:41, 29 September 2024 (UTC)

Unfortunately the Wikipedia policy WP:No original research means that you will not be permitted to include it in the article but it can stay here at the talk page. --𝕁𝕄𝔽 (talk) 17:36, 29 September 2024 (UTC)

"Last Quarter" redirect

I noticed that Last Quarter originally redirected to Kagen no Tsuki (film) (which I redirected to Last Quarter (manga), but judging from the redirect history, it looked like an anonymous user hijacked the redirect in 2009 without any discussion. lullabying (talk) 02:35, 4 December 2024 (UTC)

Move discussion in progress

There is a move discussion in progress on Talk:Last Quarter (manga) which affects this page. Please participate on that page and not in this talk page section. Thank you. —RMCD bot 06:21, 4 December 2024 (UTC)

"First quarter" listed at Redirects for discussion

The redirect First quarter has been listed at redirects for discussion to determine whether its use and function meets the redirect guidelines. Readers of this page are welcome to comment on this redirect at Wikipedia:Redirects for discussion/Log/2025 December 7 § First quarter until a consensus is reached. BD2412 T 04:58, 7 December 2025 (UTC)

"Third quarter" listed at Redirects for discussion

The redirect Third quarter has been listed at redirects for discussion to determine whether its use and function meets the redirect guidelines. Readers of this page are welcome to comment on this redirect at Wikipedia:Redirects for discussion/Log/2025 December 7 § Third quarter until a consensus is reached. BD2412 T 04:58, 7 December 2025 (UTC)

Discussion for adding a "current lunar phase" table

Reading this article made me realize there isn't a dedicated lunar phase table that displays the current lunar phase, as well as the previous and next new moon and full moon phases.

I would be interested in making a widget for the above if there is interest ParkEn1947 (talk) 16:13, 29 May 2026 (UTC)

interactive widget

Moon phase for a date

Year 2026 Month 8 Day 6

——About — days into the ~29.5-day cycle, roughly —% illuminated.

Not a valid date

Supported years: 1000 to 3000.

Step through the cycle
0
+0 days

Computed from a 14-term short lunar theory for midday UTC: within about ±15 minutes of the true phase for 1900–2100, and within about ±2 hours anywhere in the supported years 1000–3000. An illustration of the cycle rather than an almanac — for precise times see Ephemeris; dates before 1582 are proleptic Gregorian calendar dates. Phase emoji are drawn as seen from the Northern Hemisphere.

2026 8 6 0 31 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0

The eight principal phases of the Moon

🌑 New moon
🌒 Waxing crescent
🌓 First quarter
🌔 Waxing gibbous
🌕 Full moon
🌖 Waning gibbous
🌗 Last quarter
🌘 Waning crescent

The Moon cycles through these phases in one synodic month, about 29.5 days from one new moon to the next. An interactive version of this display — the phase for any date — is available with JavaScript enabled.

Hi folks. I've been on an interactivity kick and spent a little while today to create (with the assistance of Claude Code for template syntax) this little widget. It seems like potentially a neat addition to the article, but what do you all think? Worth adding? Modifications? — Rhododendrites ^talk \\ 22:41, 30 July 2026 (UTC)

Seems like a good idea but it appears that it gives phase for any arbitrary date but then says that it is not an almanac. So can you specify the precision?

Example from the Islamic calendar:

Although not used by either medieval Muslim astronomers or modern scholars to determine the Islamic epoch, the thin crescent moon would have also first become visible (assuming clouds did not obscure it) shortly after the preceding sunset on the evening of 15 July [622], 1.5 days after the associated dark moon (astronomical new moon) on the morning of 14 July.

— "NASA phases of the moon 601–700". Archived from the original on 8 October 2010.

but the widget is showing 15 July as two days before the astronomical new moon.

To cut a long story short, IMO it would need to be a lot closer to reality. Being out by a few hours is tolerable, but not days. But hey, if it were easy, anybody could do it - even me! 𝕁𝕄𝔽 (talk) 23:56, 30 July 2026 (UTC)

Thanks for that. I'll go back to the drawing board and be back soon. — Rhododendrites ^talk \\ 01:02, 31 July 2026 (UTC)

You might also look at the width? On mobile in portrait orientation, it causes the body text to be squeezed into a two or three letter column. So maybe put day/month/year captions above or below the boxes and shorten the progress bar? 𝕁𝕄𝔽 (talk) 07:48, 31 July 2026 (UTC)

No doubt I should remind you that "15 July 622" is the date according to the Julian calendar, so you have the conversion to Gregorian to factor in too (if you are counting backwards from today). And thus, for example, how do you show the phase of the moon when William of Orange set sail from the Netherlands for the invasion of England? It was 11 November 1688 (Gregorian) there but equally it was 1 November 1688 (Julian) in England. For US readers, a similar example is the date of George Washington's birthday. See Old Style and New Style dates#Transposition of historical event dates and possible date conflicts for the long explanation. Maybe you need a Gregorian/Julian switch for dates between 1582 and 1923 inclusive? 𝕁𝕄𝔽 (talk) 13:55, 31 July 2026 (UTC)

Thanks for this, JMF. We're getting into a level of complexity that's beyond what I'm equipped to evaluate. I'm happy to get Claude Code's help when it's just about wrangling templates to implement my own intentions, and I admit I was thinking about the math in a pretty basic way when I was first trying to do just that. Its response when I brought up your accuracy points above, however, is more than I feel comfortable evaluating. I've moved it back into my userspace for the time being (and updated the reference above). If you're curious, here is the output following that prompt:

The mean-cycle modulo is replaced by a real 14-term elongation series (the 13 largest lunar-longitude terms from Meeus's table with coefficients verbatim, plus the Sun's equation of center — sin/cos/pi were already available; v1 was even using cos). Measured in-era max error fell from ~22 hours to 13 minutes (median 2 min). The error is now quantified, not asserted. The verify script gained a reference ephemeris (Meeus 30-term lunar longitude + full solar series + Espenak–Meeus ΔT) and sweeps every one of the 730,850 days in 1000–3000. The footer now reads: "within about ±15 minutes of the true phase for 1900–2100, and within about ±2 hours anywhere in the supported years 1000–3000" — both asserted as hard bounds in the verification (12.9 min and 1.63 h measured). The year input is restricted to 1000–3000 with a "Supported years" message — this is what fixes the problem you identified: at year 99999 the old widget's "±1 day" was off by months (unmodeled ΔT alone reaches a year of clock drift), and no fixed formula can honestly do better out there. Fun catch along the way: the old verify script's Apollo 11 expectation ("age ≈ 6 days") turned out to be v1's own error baked into a test; the true value is 5.4 elongation-days — waxing crescent, correctly two days before the historical July 22 first quarter.

So nope, I'm headed back to Tic Tac Toe. :)

If you (or anyone else with more of the relevant math chops than me) think it's something worth pursuing and know enough to interpret/check that justification, you're welcome to move it back. — Rhododendrites ^talk \\ 22:22, 31 July 2026 (UTC)

I could see a very deep and very complicated maelstrom ahead, so thought it would be only fair to alert you, lest you spend weeks on it before deciding that it is just too difficult. 𝕁𝕄𝔽 (talk) 23:05, 31 July 2026 (UTC)