NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Time of Sun & Moon rise and set
From: Brad Morris
Date: 2016 Feb 6, 18:14 -0500
From: Brad Morris
Date: 2016 Feb 6, 18:14 -0500
Stan
Do that again, only let your assumed latitude be the pole itself.
If the singularity at the pole bothers your program, try 89° 59.9'
I suspect that 29 minutes will look very small.
Consider a star when observed from the pole. The star makes a 360° swing in azimuth over one day, yet the altitude changes only by the proper motion of the star, which is to say, negligible.
Now add the steadily increasing declination value over months and the daily culmination only occurs at the end of each day. In fact, the sun's true culmination, when viewed from the pole, occurs once per annum for each pole!!
Brad
On Feb 6, 2016 4:54 PM, "Stan K" <NoReply_StanK@fer3.com> wrote:
Everybody seems to be in agreement in answering Steve's question - the time of meridian transit is independent of latitude. But was Herbert the only one who read between the lines? Was Steve really asking if latitude has to be considered when trying to determine the time of solar meridian passage based on the maximum altitude of the sun? I doubt it, since selecting the time of maximum altitude is not that easy even at middle latitudes, let alone at high latitudes. Fortunately we are generally only trying to determine latitude from a noon sight, so it is the altitude, not the time, that is of interest.
In any case, I got curious. Just how much was Herbert's "many minutes" between transit and culmination. I selected a latitude of 89º30'N, a longitude of 0º, and a date of 22 September 2016, when the declination of the sun was changing the fastest. Transit would occur at 1153 UT (115232 by the GHA method). At this time the altitude of the sun is 32.4', but between about 1107 and about 1141 it "peaked" (to the nearest 0.1') at 32.6'. Splitting the difference and calling it 1124, this gave a difference of about 29 minutes between transit and culmination. If I did this right, then WOW!
Stan
-----Original Message-----
From: Herbert Prinz <NoReply_HerbertPrinz@fer3.com>
To: slk1000 <slk1000---.com>
Sent: Fri, Feb 5, 2016 12:52 pm
Subject: [NavList] Re: Time of Sun & Moon rise and set
Steve,You are quite right to spot a problem here. Of course, it is trivial to say that meridian transit of any given body happens at the same time for all observers on the same meridian. But for the navigator, the observable event is culmination, not transit. For a body with variable declination such as the sun, the time of culmination is indeed affected by the observer's latitude - to the extend that the method of the classical noon observation will break down near the pole. North of 89 deg, the time between transit and culmination can exceed many minutes, and thus also the time between the observed culminations by two observers on the same meridian. Besides the theoretical problem you will also face the practical one that at some point the observable will get lost in the noise.Herbert Prinz
