Talk:Equinox

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Equinox has had a peer review by Wikipedia editors which is now archived. It may contain ideas you can use to improve this article.

Which of the following is a better sentence?

  "A zebra is a zoological term for when an animal has a long neck."

  "In zoology, a zebra is an animal with a long neck."

The former sentence is how this article and the ones on vernal equinox and autumnal equinox were written.

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Improving an article is good, but there is no need for unfriendly remarks. Patrick 21:48 Nov 2, 2002 (UTC)

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lol Lir 00:06 Nov 3, 2002 (UTC)

Contents 1 mathematical calculation 2 Factual accuracy questions 3 Merge 4 Help with confusion 5 Lead section 6 Spring/Autumn ? 7 Image 8 Aurora Borealis 9 Equilux 10 When are the days equal? 11 Not to be offensive 12 What does this have to do with the actual Equinox?

[edit] mathematical calculation

"The time at which the sun passes through each equinox point can be calculated precisely—so the equinox is actually a particular moment, rather than a whole day."

I was wondering, how accurate the equinox can be found out. Certainly the mathematically exact moment can not be calculated. The sea quake in the Indian ocean 2004 tilted earths axis by several centimeters so with enough wobbling or vibrations there might even be multiple spring/autumn equinoxes per year. So, is the calculated precision of equinoxes a matter of seconds, ms, us, ns?

There is a difference between the "rotation axis" of the earth and the geographical location where this axis intersects the surface. Because of conservation of angular momentum, the rotation axis cannot be changed by events on earth and so the celestial equator is fixed in space and equinoxes can be determined very accurately (sorry to admit I do not know the current margins). The wobbling mentioned is the movement of the earth's crust relative to the rotation axis and has no bearing on the time of equinox. −Woodstone 12:04, 2005 Mar 28 (UTC)

You are correct that the rotation axis itself cannot be changed by events on earth. However, the 2004 Indian Ocean earthquake article also mentions that "theoretical models suggest the earthquake shortened the length of a day by 2.68 microseconds", which throws off most time calculations by nearly 1 millisecond/year.

It would be nice if this article mentioned the actual formula for calculating the equinox. (If it's too ugly and scary-looking, maybe add a link to some other web page with the actual formula). Alas, my quick Google turns up many pages that mention the book "Astronomical Algorithms" by Jean Meeus, but don't give the actual formula.

[edit] Factual accuracy questions

This article makes two claims which contradict others on the 'pedia. I am uncertain of exactly which is right/wrong, but I suspect this one is:

1. Article claims that at equinoxes day/night are equal. Vernal equinox article says that is not true, and that day/night equal day occurs a few days before or after equinox.
2. Article claims that at poles sun passes from six month day to six month night & vice versa. Other articles (Midnight sun, Polar night) imply the period at the poles is not quite six months day/six months night, but slightly less.

Also, article should explain what a sidereal equinox is, and how it differs from a normal one. --137.111.7.212 10:27, 9 September 2005 (UTC)

It is not a question of right or wrong. It depends on the definition of day versus night.

• Simple definition:
  • day is the period that the true position of the middle of the sun is above the horizon
  • the day and night are equal at the equinox
  • polar night and day are half a year each
• More common definition:
  • day is the period that some direct light of the sun reaches the ground in absense of local obstacles
  • this definition makes the day longer by some 7 minutes or more (width of solar disk plus atmospheric refration)
  • equal day and night occurs a few days before the vernal equinox and a few days after the autumnal equinox
  • polar day is much longer than polar night (and very long twilight)

I will add a short explanation in the text and remove the banner.−Woodstone 20:31:58, 2005-09-09 (UTC)

• Also, the picture in the introduction is kind of flat, anyone have a real satalite photo they'd like to share?--Hello'from^'SPACE 23:48, 14 November 2005 (UTC)

[edit] Merge

In response to the suggestion that the entry for 'Equinox' be merged with the entry for 'Equinoctial Point', I favour the retention of the term 'Equinox'. The purpose of an encyclopaedia is to provide access to information to people who may know little about a topic. Otherwise why are they looking it up? Equinox is a term more likely to be used in such cases. The term 'Equinoctial point' can be covered within that entry and in its own entry if more detail is required. P J Lock 130.220.79.98 00:17, 28 September 2005 (UTC).

I have merged Equinoctial Point into this article, as per listing in Category:Articles to be merged. Brisvegas 03:10, 10 October 2005 (UTC)

fixed--Hello'from^'SPACE 00:27, 15 November 2005 (UTC)

[edit] Help with confusion

I am confused when reading this article because it says on the equinox, day and night are of equal length, 12 hrs each. But from the Sunrise and Sunset times given in my World Almanac, it seems this occurs a few days before the equinox. I was hoping for some kind of simple explanation for why this is so. Thanks ፈቃደ (ውይይት) 22:52, 28 December 2005 (UTC)

Never mind, I see now that the article does give it, I just wasn't reading carefully enough... ፈቃደ (ውይይት) 22:54, 28 December 2005 (UTC)

You can find slightly more information in the article day. −Woodstone 22:57, 28 December 2005 (UTC)

Thanks, I added to that article the Damascus Document's definition of when the Sabbath begins: "No one is to do any work on Friday from the moment that the sun's disk stands distant from the horizon by the length of its own diameter... What I am wondering now is, if one were to define "night" as beginning at that time, and "day" as beginning when the sun was a corresponding distance from sunrise, it would make the day a bit shorter than the night, instead of longer, right? So by that definition, would there be an equinox, and would it occur a few days after the accepted equinox instead of before, and how could it be calculated? ፈቃደ (ውይይት) 23:42, 28 December 2005 (UTC)

Interesting observation. If the sun's disk stands its own diameter from the horizon, that would make the center 16'+32'=48' above the horizon. Subtracting the atmospheric lift of 34', the true position of the sun would be 14'. So indeed the day by this definition would be shorter than the night. The effect is opposite and about 1/3 of the size compared to the modern definition.

Your edit in the article is incorrect. Equinox is defined by the astronomical position of the sun, not the daylight observed. The deviation in time because of the elliptic orbit of the Earth is only about +/- 15 minutes.

−Woodstone 10:44, 29 December 2005 (UTC)

The elliptic orbit seems to mean the Earth is getting more sunlight on one hemisphere for six months even though it's passing farther away, simply because it's tilted toward the Sun during that time, so just facing the Sun does more to affect the seasons than actual distance from it. ፈቃደ (ውይይት) 13:41, 29 December 2005 (UTC)

[edit] Lead section

The lead section does not summarize the entire process of an equinox. There is no mention of what dates the equinoxes occur, and it does not explain how long the daytime and nighttime last. (Twelve hours would be a fair hypothesis, but when you look into it, a true equinox divides approximately eleven hours and fifty-some minutes between both the day and night.) The graph does not properly display equinoxes and should be replaced; perchance I will create one myself. Any suggestions concerning my comments? Eternal Equinox 19:44, 28 January 2006 (UTC)

I am going to copy-edit the article since some of my edits were reverted. –Eternal Equinox 21:03, 31 January 2006 (UTC)

The last few edits have created quite a lot of redundancy in the article. The ecliptic/equator and length of day/night issues are both explained three times. Major clean up will be needed. −Woodstone 09:35, 1 February 2006 (UTC)

Agreed, I'll get around to doing that whenever I have the time. Could one please explain this edit? The way I look at it is that once we reach the year 2050, there will be fifty years placed in the article. Is this really necessary? —Eternal Equinox | talk 23:17, 1 February 2006 (UTC)

There was still a lot of reduncancy after the recent clean up. I have now moved the full discussion of "equal night" into the lead section. The more detailed astronomical description and equinoctial point is drawn together with (almost?) complete elimination of redundancies.

I see no harm in having a table with precise date and time for e few years back and quite some years ahead as long as it does not pass beyond the regular text of the article. −Woodstone 14:35, 4 February 2006 (UTC)

IMHO, the following far-better explains what an equinox is :

"Every year, around March 20th (occasionally the 21st) and then six months later around September 23rd (occasionally the 22nd), our planet reaches a position relative to the Sun wherein, if it had no atmosphere and was perfectly spherical, its north and south poles would be simultaneously poised on the plane of the Earth's terminator (the globe's boundary line between night and day). These two moments on our calendar are referred-to as equinoxes." (added to the main article 8/31/06 by earrach)

Of course, considering those IF's, I suppose we wouldn't be having this conversation, eh? Regardless, I think the above idealized definition is a highly instructive "seed-point" for the discussion and would suggest you consider trying it on your students. Please, ANYTHING other than that utterly despicable "...when the sun crosses the celestial equator." -line used virtually everywhere else. Ugh, ugh, ugh. It "explains" n o t h i n g. earrach

The standard explanation is used because it is indeed used everywhere else. The fundamental and most easily understood definition of an equinox is already in the opening paragraph, that days and nights are equal. That can easily be the opening definition. Your proposed paragraph does not follow Wikipedia style which requires that the title of the article to be the subject of the first sentence, that is, that the title of the article be defined before any explanations are given. I do not regard the positions of the north and south poles relative to the terminator as being particulary instructive for the equinox. It does not belong at the head of the article. — Joe Kress 07:48, 1 September 2006 (UTC)

I am considering your other points but your statement about the day and night being equal as the fundamental descriptor, although being the derivation of the word "equinox" -is- technically inaccurate and has in point already caused quite a lot of discussion here and I fear will continually keep this article's content in dispute without my help. Due to our atmosphere, the globe as a whole always has more day than night because the lit "half" of the globe is always more than half: the sunset and sunrise both "over-wrap" the ideal terminator due to refraction - - a fact that I have imbedded in my suggested revision for a "standard" definition. This pushes the local "equal-night" dates off, subjectively/calendrically, relative to the official date which is determined from when the Earth, due to its orbit and tilt, reaches orientation implied in my preferred definition. Unfortunately for purposes of clarity, the only way of being both accurate concise regarding the "equal-nights" would be to be intentionally fuzzy: "The days around the equinoxes have approximately equal days and nights." - and we know how wikipedians deal with fuzzyness. 9/6/06 earrach

[edit] Spring/Autumn ?

The March equinox is only in the Spring in the Northern Hemisphere. Down in the South, it's in the middle of the Autumn. Furthermore, Spring doesn't start on the equinox - it starts halfway between the solstice and the equinox. The equinox would be mid-spring or mid-autumn. 2006-03-02 16:42:17 Vhata

Where exactly in this article do you see the North-centricity? I cannot find it. I see it explaining both ways. Whether spring starts at the equinox or halfway from the solstice is a matter of local culture. Again, where precisely in this article is it biased? For a more extensive comparison, see season. −Woodstone 19:33, 2 March 2006 (UTC)

I was going to make the same remark as the original poster here. There does seem a bit of 'North-centricity' in the table with dates & times at the beginning of the article. By stating 'March (spring starts)' or 'September (Autumn starts)' or however it's exactly put up (don't have firefox at work, can't open tabs!), it's showing a northern-hemisphere bias. It seems like these references connecting specific equinoxes with seasons should either be removed, or prefaced with 'in the northern/southern hemisphere...' 140.142.226.76 19:37, 7 March 2006 (UTC)

You were both right, I overlooked the table. It has been corrected now. −Woodstone 20:21, 7 March 2006 (UTC)

There is also the point that only the temperate climates (between polar circles and tropics) have 4 seasons. In the tropics there are only 2, wet and dryShniken 04:21, 15 March 2007 (UTC)

[edit] Image

The image that shows the rays of the sun hitting the earth is perhaps a bit inaccurate. The north pole of the earth should probably be tilted 23.5 degrees toward or away from the viewer (ie, we should be able to see either the north or south pole), since most people will assume that the image is perpendicular to the earth's orbit. 68.6.85.167 01:11, 5 May 2006 (UTC)

The image they've used is actually correct but virtually useless due to the orientation of the view. The image I have always used (see my original rendering below) sidesteps this problem and IMHO, illustrates the -reason- for the equinox pictorially like no other diagram does...

...I thought I was the only one who ever thought to "look-down" on the whole pattern for clarification it but did find find one a bit similar but not really the same up in the corner of a page in Guy Ottwell's good old "Astronomical Companion". Now THERE is a great illustrator of astronomical ideas! Earrach 22:46, 21 June 2006 (UTC)

You should be clear that this is from a NORTHERN hemispheric perspective. Arthurian Legend 04:35, 21 March 2007 (UTC)

[edit] Aurora Borealis

What are the effects the Equinox has on the Aurora Borealis? 71.112.224.112

[edit] Equilux

Statment moved from article:

• Although the word "equinox" implies equal length of day and night, as is noted elsewhere, this simply isn't true. But for most locations on earth, there are two distinct identifiable days a year where the length of day and night are the closest to being equal. Those days are commonly referred to as the "equiluxes" to distinguish them from the equinox. The equinox is a point in time, but the equiluxes are days. By convention, the equiluxes are the days where sunrise and sunset are closest to being exactly 12 hours apart. This way, you can refer to a single date as being the equilux, when, in reality, it spans sunset on one day to sunset the next, or sunrise on one to sunrise the next. As an example, for a city 45 degrees N and 123 degrees W (Portland, OR), the 2006 autumnal equilux is on Sept 25 when sunrise is at 7:01 am and sunset is at 7:02 pm. The 2006 autumnal equinox is on Sept 22 at 9:03 pm. Note that for the Northern Hemisphere, the autumnal equilux lags behind the equinox, and the reverse is true in the spring. As you might suspect, the whole situation is also reversed for the Southern Hemisphere.

I cannot find any substantial support for the name "equilux" on Google. Please provide a good citation for its "common" use and for its "conventional" meaning. If not, then reword without "equilux". — Joe Kress 07:01, 24 August 2006 (UTC)

From google:

http://groups.google.com/group/sci.astro/browse_frm/thread/95431b5b56640874/d6ae5b193523fbfa?lnk=st&q=equilux&rnum=3&hl=en#d6ae5b193523fbfa

The term equilux is discussed and used by both professional and amateur astronomers from organizations as diverse as the Lick Observatory and Swedish Amateur Astonomer Federation (SAAF) going back at least 12 years. OK to move statement back?

Wiredknight 22:32, 24 August 2006 (UTC)

Maybe equilux its own article? (with a link from equinox) --Tauʻolunga 23:33, 24 August 2006 (UTC)

Thanks for the citation. If the paragraph is moved back, the ref must be included. I do remember a rather detailed discussion in another article on a related subject that mentioned the semi-diameter and refraction of the Sun. I'm not sure whether it discussed earliest sunset/latest sunrise (near winter solstice) or something akin to 'equilux'. So it is discussed elsewhere on Wikipedia in some form, which may or may not be more appropriate. — Joe Kress 04:37, 26 August 2006 (UTC)

It's described in for example in the wiki article day. −Woodstone 12:33, 26 August 2006 (UTC)

The article I was thinking of was equation of time, which was actually discussing something related but different, the shift of sunrise/sunset times caused by tilt and eccentricity. However, this shift does not change the relative amount of daylight and nighttime. — Joe Kress 05:03, 27 August 2006 (UTC)

[edit] When are the days equal?

The sentence "The real equality of day and night happens a few days towards the winter side of each equinox." appears to be incorrect because as written the winter side is dependent on which hemisphere you are in. Readers in different hemispheres would assume opposite meanings. Personally I do not know the correct solution, but I would like to read what it is. --Roger Bays 05:11, 19 March 2007 (UTC)

Well, the correct solution is, "In the Northern Hemisphere, the real equality happens before the March equinox and after the September one. In the Southern Hemisphere, after the March one and before the September one." So the sentence is not uncorrect, but probably a bit ambiguious. I agree that readers may be confused. Rija 14:40, 19 March 2007 (UTC)

Indeed it seems that the formulation in the article is a bit sloppy in suggesting that the day and night can be equally long at the equator. On the equator precisely, looking at only the true position of the Sun (midpoint, no atmospheric lifting) the time between successive passings of the horizon is always 12 hours. So still at a position on the equator, but now taking into account the diameter of the apparent Sun's disk and the atmospheric lifting, the day is always longer than the night. Only at positions far enough from the equator to eliminate these effects by a shortening day (and equal lengthening of the night), the day can be equally long as the night. These positions are always located in a well defined hemisphere, so the concept of winter is well defined. −Woodstone 19:34, 19 March 2007 (UTC)

[edit] Not to be offensive

but this is English Wikipedia and the equinoctes (equinoxes) aren't known by their Chinese names at all, so i'm going to delete that. there is already a separate section on the equinox in East Asia therefore it is redundant to state that information twice

[edit] What does this have to do with the actual Equinox?

Okay seriously... Solar terms in East Asia

Main articles: Chunfen and Qiufen

The traditional East Asian calendars divide a year into 24 solar terms (節氣). Chūnfēn (pīnyīn) or Shunbun (rōmaji) (Chinese and Japanese: 春分; Korean: 춘분; Vietnamese: Xuân phân; literally: "vernal equinox") is the 4th solar term. It begins when the Sun reaches the celestial longitude of 0° and ends when it reaches the longitude of 15°. It more often refers in particular to the day when the Sun is exactly at the celestial longitude of 0°. In the Gregorian calendar, it usually begins around March 20 and ends around April 4 (April 5 East Asia time). Qiūfēn (pīnyīn) or Shūbun (rōmaji) (Chinese and Japanese: 秋分; Korean: 추분; Vietnamese: Thu phân; literally: "autumnal equinox") is the 16th solar term. It begins when the Sun reaches the celestial longitude of 180° and ends when it reaches the longitude of 195°. It more often refers in particular to the day when the Sun is exactly at the celestial longitude of 180°. In the Gregorian calendar, it usually begins around September 23 and ends around October 8. The Chinese character 分 means division, so the vernal equinox and the autumnal equinox signify the middle of spring and autumn, respectively, unlike in Western cultures.

This should be in the SEE ALSO section and its own article or in an later paragraph, not the initial paragraph about its name in English. Did the words Chungen and Qiufen have any influence on the word aequus nox? No? Then it doens't belong in this section. IT DEFINITELY does not belong in the beginning of this article as it doesn't explain what an equinox is and it is not relevant to the definition or the important of equinoxes in the English speaking/Western world. —The preceding unsigned comment was added by Arthurian Legend (talk • contribs) 04:42, 21 March 2007 (UTC).

That section was moved from near the end of the article to its present position near its beginning (with some modification) by Yao Ziyuan on 25 November 2006. Obviously, he didn't want it near the end of the article. However, I agree that in this English version it doesn't belong near the beginning because interrupts the explanation via an excursion. — Joe Kress 20:42, 21 March 2007 (UTC)