Talk:Length of daytime

This is not too technical. There are already quite a few related entries, such as sunrise, sunset, declination, zenith, azimuth, etc.. Day length is simply the time from sunrise to sunset. --Roland 04:23, 28 April 2006 (UTC)

Do you have any references for this information? Kevin 09:44, 2 May 2006 (UTC)

They are available in any book about solar radiation. --Roland 22:05, 3 May 2006 (UTC)

What I meant was did you have any specific references/citations that you could put into the article, so that a layman could look up the information. Kevin 01:03, 4 May 2006 (UTC)

Follow the external links. Gulliveig 09:48, 3 March 2007 (UTC)

Julian Day

In the chart, the term "Julian Day" is incorrectly used to mean "day of the year". Numbering the days of the year from 1 to 365 (or 366) is a common way of reckoning dates, but it is NOT the "Julian Day." See the wikipedia entries for "Julian Day" and "ordinal date". - M 2006-07-24

Thanks for pointing this out. It has just been corrected in the redone plot. --Roland 00:58, 21 November 2009 (UTC)

Question

I have a question- where can I learn about how the length of day differs at any given latitude?

Please title and sign your comments. Although comments are no FAQ, the answer is easy to provide: for a good primer follow the external links to the formulas ;) Gulliveig 09:48, 3 March 2007 (UTC)

I have the same question, how to calculate the sunrise and sunset for a given latitude and day. I expected to find the information on this page or the suggested merge page (Daytime) but both seem to go to great lengths to avoid the underlying math. — Preceding unsigned comment added by 149.32.224.35 (talk) 15:38, 30 October 2013 (UTC)

If you look at page 515 of the Explanatory Supplement to the Astronomical Almanac (3rd ed.) you will see it is an iterative procedure (that is, guess and check). To carry out the procedure, further algorithms are needed to calculate the position of the sun in equatorial coordinates. So trying to describe it in the article would be very involved. Jc3s5h (talk) 21:10, 30 October 2013 (UTC)

Day Length increases

I thought that the spin of the earth was gradually decreasing, and hence the length of day was gradually increasing. I seem to remember something like 16 hour days during the age of the dinosaurs. There is no mention of this here. Does anyone know enough about it to write it up here?

Anthony Wood

Agreed : but there should be someone better able than I. 82.163.24.100 (talk) 13:36, 19 November 2007 (UTC)

What you are talking about is the length of the solar day, which is a property of the Earth, currently about 24 hours, which is the length of time between one noon and the next. What this article is talking about is the length of time between sunrise and sunset, which varies depending on location and season. --Spoon! (talk) 08:04, 15 December 2007 (UTC)

Given the ambiguous name, the article should talk about both, or link to another article that talks about length of the solar day. —Preceding unsigned comment added by 89.103.130.151 (talk) 10:02, 14 July 2009 (UTC)

I've added an extra section and link to the Tidal Acceleration article which talks about this. Robert Walker (talk) 18:57, 5 November 2010 (UTC)

Meaning of Day Length

There are two different types of meaning; basically the length of the daylight and the interval between midnights. They need separate treatments.

For the interval between midnights, there are I think at least three types of variation :

• Systematic during each year - orbital geometry - Equation of Time
• Other Short term - changes in moment of inertia - Leap Second variation
• Long term - tidal dissipation - recession of Moon.

It may be almost sufficient to link to the corresponding pages.

82.163.24.100 (talk) 13:36, 19 November 2007 (UTC)

The latter is the length of a solar day. You can link to that. --Spoon! (talk) 08:12, 15 December 2007 (UTC)

when is it daylight? graph?

Elsewhere in Dawn there is reference to astronomic dawn, nautical dawn and civil dawn. In some countries there is also lighting-up time which in England was 30 minutes before sunrise and after sunset.

For an example site, such as London, how would these three dawns & sun-dawn show on a graph?? Salisbury-99 (talk) 09:16, 22 September 2008 (UTC)

"Generally" 12 hours of Daylight on Equinox?

I live in Denver, CO, elevation 5,280 feet and during the equinox the length of day seems to be 12 hours and 10 minutes. In Leadville, CO, elevation 10,152 feet, the length of daylight seems to be 12 hours and 20 minutes during the equinox. Is this due to altitude/elevation causing the sun to be above the horizon relative to those locations for a longer period of time? My guess is that the "12 hours everywhere" rule is based on an assumption that the whole earth sits at mean sea level. Seeing as how much of the earth is NOT at mean sea level, this general rule has some major exceptions. Might be worth explaining this in the article. Leahcim506 (talk) 07:42, 16 April 2010 (UTC)

See for a more complete explanation Equinox#Length of equinoctial day and night. Most important effects are the size of the Sun, the atmospheric lift, and latitude. Altitude has a very minor effect. −Woodstone (talk) 12:52, 16 April 2010 (UTC)

Mathematical function?

Any chance of a math function to compute the length of a day based on latitude and time since the winter solstice?--99.110.255.113 (talk) 17:28, 19 November 2010 (UTC)

Hours of daylight vs latitude vs day of year Chart

I found the chart somewhat difficult to interpret.

For one thing, the 12 hr contour line should be made symmetrical, although the color codes would still be different for daylight vs night.

If you added a second nocturnal 12 hr contour, then what is the space between the contours? Should the 12 hr contour be represented by straight lines? an "H" shape? With perhaps an 11 hr contour being a closely associated curve.

I would also encourage adding a chart summary directly below the chart.

Mark the Arctic/Antarctic Circle on the chart (66° 33′ N/S respectively), with associated 24 hr/0 hr contours. Perhaps also indicate the equinoxes (sun above equator) and solstices (sun above tropic of Capricorn/Cancer).

A legend?

Brown - 23 to 24 hrs daylight, 0 to 1 hr night (see notes above, I'd adjust to actually 24/0). White for daylight, black for night?

Orange - 18 to 23 hr daylight, 1 to 6 hr night.

Yellow - 14 to 16 hr daylight, 6 to 10 hrs night.

etc. Keelec (talk) 19:23, 1 April 2012 (UTC)

Yeah, I think that there are some issues with this graph. Either the label that says 1 hour is meant to be 0 hours; and the label that says 23 hours is meant to be 24 hours; or the graph should have displayed the 0 and 24 hour contours instead of the current 1 and 23 hour contours. Can someone who understands the Sunrise equation please produce a better graph? Thank-you, --123.243.217.67 (talk) 17:40, 2 August 2014 (UTC)

average day length?

If I understand right, section "Some interesting facts are as follows:" says the Equator's average day length is 12 hours and "about 7 minutes" and northern hemisphere's day length is "a few minutes" more than southern hemisphere's.
But, what are the extremes? Where are the longest and shortest average day lenghts? It could probably be figured from the "Day length vs latitude" diagram, but I didn't know how to do it. 85.217.36.130 (talk) 01:26, 26 June 2012 (UTC)

The major reason that the average day is longer than 12 hours, is the fact that some light reaches a place from the sun, even when its centre is a little below the horizon. So the difference is greatest where the sun spends the most time slightly below the horizon. That is where it rises and sets at the most oblique angle, which would be at the poles.−Woodstone (talk) 07:47, 26 June 2012 (UTC)

Yeah, I found a finnish language source "Valoisan ajan pituus" (Length of daylight time) [[1]], which has the text Kun tarkastellaan vuoden mittaista ajanjaksoa, niin pohjoisnapa ympäristöineen on valoisin paikka maapallolla ja vastaavasti etelänapa ympäristöineen vähävaloisin paikka. Translation: When examining a year's time, the north pole and its surroundings are the brightest place on earth and respectively the south pole and its surroundings have the least light. 85.217.36.130 (talk) 03:11, 28 June 2012 (UTC)

That seems incorrect. Indeed, because the sun is somewhat more than half the year in the northern hemisphere the north pole would receive light the longest time annually. However for the reason stated above, the south pole would come right after the area around the north pole. For the shortest time light is received close to the equator. −Woodstone (talk) 08:14, 28 June 2012 (UTC)

Earth article's infobox has this: Inclination: 7.155° to Sun's equator

I think that means the north pole is leaned to the Sun quite some time. That should prove the claim right. And, the claim is made by Tampere section of Ursa, an astronomical association in Finland, and I believe they indeed should know it. 85.217.40.33 (talk) 04:59, 25 May 2013 (UTC)

It's the inclination of the orbital plane. Nothing to do with the poles. −Woodstone (talk) 08:37, 25 May 2013 (UTC)

day length throughout history

just a friendly reminder to include that...considering it was shorter at the start of this planet Paranoid Android1208 (talk) 02:46, 30 May 2013 (UTC)

I rewrote that part using information from Tidal acceleration and Earth's_rotation an removed the original reference, which is admittedly the scientifically looking reference that is easiest to find in google, but is clearly crackpot science. Not only is it published in a dubious journal, but it is trying to explain the well understood process of tidal acceleartion by linking it to the Hubble constant, which is completely irrelevant at the scale of a single planetary system. 79.246.26.107 (talk) 14:05, 29 September 2013 (UTC)

Move to "Length of day"?

The term "length of day" is standard. Where is it referred to as "day length" except in this article? Vaughan Pratt (talk) 00:37, 9 December 2014 (UTC)