Talk:Sunrise equation

message: Am I correct that the equations presented do not take into account the altitude of the observer? DrMattB (talk) 21:47, 29 December 2014 (UTC)
thread_title: Untitled and out of chronological sequence

message: I programmed the algorithm and it works fine. Two questions are open: What's the time area the algorithm is valid and between which latitudes does the algorithm give reasonable results?  —Preceding unsigned comment added by Hgs07 (talk • contribs) 20:11, 20 September 2010 (UTC)
thread_title:  Validity of the Algorithm 

message: I had programmed by the algorithm, but the result for shanghai is far from correct.
* Computed sun rise time for Shanghai in March 20th: 10:12AM(CST) 
* Correct sun rise time for Shanghai in March 20th: 5:59AM(CST)
Can anyone else double-check the algorithm? Thanks --Mountain (talk) 06:10, 20 March 2011 (UTC)
thread_title:  The algorithm seems to be not valid 

message: Does anyone know why the Equation of Centre is calculated as a length but is then used as an angle in the Ecliptic Longitude?
77.89.154.66 (talk) 12:34, 6 September 2013 (UTC)
replies: text: In the celestial sphere, arc lengths are angles. Specifically, the Equation of the Center is an arc length along the ecliptic, and is used as a correction to the Mean Anomaly to get the true ecliptic longitude. 2001:4452:3A9:7500:2B24:195C:3B8F:BFAC (talk) 11:14, 20 May 2022 (UTC)
thread_title:  Equation of Centre: Length or Angle? 

message: Why is this constant used throught the algorithm, why not instead explain what it is (I believe it to be J2000, that is, the Julian date of January 01 2000 at 12 noon http://docs.kde.org/stable/en/kdeedu/kstars/ai-julianday.html )
More curiously, though, is the 0009 that is sometimes attached to the constant does anyone know its relevance? 
Ok, a bit of googling shows that the algorithm described on this page is also shown on http://users.electromagnetic.net/bu/astro/sunrise-set.php  With a bit more explanation of what constants mean AND a link to more definition, BUT the link is dead, thank the Wayback machine for the following http://web.archive.org/web/20040707121402/http://www.astro.uu.nl/~strous/AA/en/reken/zonpositie.html  — Preceding unsigned comment added by 124.197.2.81 (talk) 18:18, 19 September 2013 (UTC)
thread_title:  2451545 

message: 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) 18:15, 2 August 2014 (UTC)
thread_title:  Error; or the need for alternative contours 

message: The section called "Calculate current Julian cycle" says, "n is the Julian cycle since Jan 1st, 2000." But Julian cycle is not defined.
Julian day defines related concepts, but not "Julian cycle" per se.
Google search on "Julian cycle" leads to pages like http://www.hermetic.ch/cal_stud/jdn.htm and http://whatis.techtarget.com/definition/Julian-date, which say that a Julian cycle is the 7980-year period starting at 4713 BC. The Julian day article defines this as the Julian period. Could a Julian period be what the "Calculate current Julian cycle" section refers to? It doesn't seem to be, since "Julian cycle since Jan 1st, 2000" wouldn't mean "current Julian cycle" -- the latter would start from 4713 BC, not 2000 AD. And whereas the Julian period is 7980 years long, the "current Julian cycle" referred to here seems to be very short, e.g. 15 years in 2015.
The only "cycles" talked about in the Julian day article are the indiction, Metonic and solar cycles. But it's pretty clear that these "subordinate cycles" are not what the "Calculate current Julian cycle" section refers to.
My guess is that in the "Calculate current Julian cycle" section, "current Julian cycle" means "the number of days since the J2000 epoch." Maybe there's a more concise and accurate term for that, but "Julian cycle" is apparently not it. If we can't find a concise and accurate term, we should probably change it to a long-but-accurate phrase. But hopefully someone who understands this better than me can offer a better solution. Huttarl (talk) 22:19, 29 September 2015 (UTC)
thread_title:  What does "(current) Julian cycle" mean? 

message: It appears the equation of time needs to be added rather than subtracted.
I found the change in terminology between mean solar noon and mean solar time confusing. It is mean solar noon. 
Julian Date should refer instead to JDN, Julian Date Number. It needs to be an integer for the rest to work. Showing a decimal 2451545.0, just furthers the confusion.  — Preceding unsigned comment added by 184.100.67.177 (talk) 21:18, 9 March 2016 (UTC)
thread_title:  Just implemented this in code 

message: Since this is showing up in here we might as well reference it. https://en.wikipedia.org/wiki/National_Oceanic_and_Atmospheric_Administration  — Preceding unsigned comment added by 2601:242:4000:7812:84CB:CCDA:1AA:53E9 (talk) 16:25, 23 November 2016 (UTC)
thread_title:  0.0008 Leap Seconds 

message: At the beginning of the section on the theory of the equation, its says: "The Earth rotates at an angular velocity of 15°/hour."  While taking that as true actually gives the correct answer to the problem, it is in fact not correct.  (It works because the starting point for the problem needs to be what this statement is meant to reflect, rather than what it actually says.
The Earth actually rotates one full turn on its axis in just a tad more than 23 hours, 56 minutes.  So in fact, the Earth rotates at an angular velocity of about 14.955 degrees per hour.  But of course, to go a full noon-to-noon or midnight-to midnight cycle, the Earth has to turn just shy of 4 minutes of arc farther.
But 15 degrees is actually the correct value to start from because what we are considering is not the actual rotating of the Earth, but the apparent path of the Sun seems to take, as it seems (from where we stand) to go around the Earth.
Perhaps a better statement would be, "On average, the Sun, in its apparent path around the Earth, appears to move 15 degrees per hour along that path."  Or perhaps someone can recast that to improve it.  Uporządnicki (talk) 15:20, 17 January 2017 (UTC)
replies: text: You're assuming the coordinate system has to be inertial.  Just make it one in which the line containing the Sun and the Earth is stationary and the stars are rotating about the Earth's axis at one revolution every 18³×7×773 = 31556952 seconds, close enough for government work. (This is exactly the average number of seconds per year, averaged over any consecutive 400 years of the Gregorian calendar, which is a significantly better approximation of reality than the Julian calendar.) Vaughan Pratt (talk) 04:44, 15 July 2017 (UTC)
thread_title:  Theory of the equation--a nitpicky problem? 

message: I'm working with light data from tags on Atlantic bluefin tuna, which clearly show sunrise, sunset, and Julian day (to within a few seconds).  I'd like to know the latitude and longitude of the animal at local noon of that day, at least on the real projective plane (on the sphere there are two solutions).  Is there a published algorithm for this problem?  It's not hard to derive but I'd prefer to use what's already known.  Vaughan Pratt (talk) 04:44, 15 July 2017 (UTC)
thread_title: The inverse problem

message: The "Declination of the Sun" section uses λ in its equation but does not describe what λ represents.  I'm new to this and have no clue. 2600:1700:8D90:A2B0:213:72FF:FE32:59B5 (talk) 16:39, 3 September 2018 (UTC)
thread_title:  Declination of the Sun and lambda? 

message: Out of curiosity, what are the symbols used for the hour angle?  A lower-case omega and ... a subscript zero?  A subscript letter "o"?  Something else? 2600:1700:8D90:A2B0:213:72FF:FE32:59B5 (talk) 16:31, 11 June 2019 (UTC)
replies: text: A strange choice anyway. A more logical choice would be H, this is what you will find in the traditional books on spherical astronomy. AstroLynx (talk) 16:40, 11 June 2019 (UTC)
thread_title:  Symbols in the equation?  

message: I've implemented it in code and it appears to be accurate, but upon testing I noticed some coordinates didn't work and realized those coordinates and times were for when there are no sunsets nor sunrises which results in \cos \omega_\circ being greater than 1 (for 24 hour night) or lesser than -1 (for 24 hour daylight) so attempting to get the value of \omega_\circ will return an error. That section should make an observation for that  — Preceding unsigned comment added by Jack mcslay (talk • contribs) 01:11, 13 December 2019 (UTC)
thread_title:  Perpetual day/night 

message: Considering the statement from the [Solar Transit] section:
: EOT = 0.0053 \sin M - 0.0069 \sin \left( 2 \lambda \right)  is a simplified version of the equation of time. The coefficients are fractional day minutes.
The equation can be seen on Equation_of_time#Equation_of_time in a slightly different form:
: minutes
With
:
But these are each others negative, i.c.:
:
Is there something wrong with any of these pages?
"The coefficients are fractional day minutes." is incorrect; these are fractional days.
Mmjo (talk) 09:38, 9 April 2021 (UTC)
thread_title:  Equation of Time 

message: Are there any well-established formulae for accounting for the fact that higher atmospheric pressure and lower temperature increase the refraction of sun's rays, thus effectively hastening sunrise and delaying sunset? Irfan (talk) 02:29, 25 April 2022 (UTC)
thread_title:  Accounting for atmospheric temperature and pressure effect on refraction? 

message: For mean solar time, Python code uses: J_ = n + 0.0009 - l_w / 360.0. But the 0.0009 constant isn't in the Mean solar time formula in the article. 77.99.36.144 (talk) 09:43, 27 March 2024 (UTC)
thread_title:  Python code doesn't match with formulas in text