Talk:Celestial navigation
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[edit] Some questions
Can you not use a theodlite to make the measurements? Can we please have something on this.
Would you not measure 3 stars/ objects as opposed to two and then use triangulation?
Isn't spherical trigonometry involved? in which case I would not call it "simple".
[edit] Possible error
I don't think this is quite right:
- "If you measure the angle to Polaris and find that it is 60 degrees away from directly overhead, then you are on a circle 60 degrees away from the north pole. This circle coincides with a circle of 60 degrees of geographic latitude."
If you are on a circle 60 degrees away from the north pole, then that would correspond to 30 degrees of geographic latitude, since latitude is measured from the equator.
for every degree moved away from the equator (in this case north), the star in question (Polaris) will "move" one degree towards the zenith. => if standing at the equator, Polaris will be located on the horizon, as you move towards the pole, Polaris will slowly seem to move at the same rate.
[edit] What happened...?
This article is totally empty! There's nothing after the title and the words "From Wikipedia, the free encyclopedia."
Erik 22:21, 6 October 2006 (UTC)
[edit] Polynesian celestial navigation
Should this topic include a paragraph on Polynesian navigation? Using 'star paths' of stars on the horizon, rather than stars near the zenith?
[edit] "Sights on the moon, planets and stars allow navigation to occur at night or when clouds obscure other objects"
This statement, and the omission of the actual process of taking sights may be misleading to the reader. Sun sights, and if it is visible, sights of the moon can be taken during daylight. However, since the measurement of the angle between the celestial body and the horizon requires that both be visible at the same time, the impression given by the quoted sentence that observations can be taken at night, is not correct. Since stars are generally not visible during daylight (not completely true, but a fair generalization) and the horizon can't be observed in darkness, star sights are taken only at twilight a period which is several minutes long (longer at temperate latitudes and less in the tropics). The routine one would follow, if relying on celestial navigation and wanting to do the full process is to prepare in advance for the dawn twilight by figuring out in advance the approximate azimuth and elevation of several stars that produce good non acute angles in the lines of position they will produce. By having them figured out in advance, the sextant can be preset, and, together with a compass, the sought star can be picked out easily, several sights can be taken, and then you can move on and shoot the other selected stars, the more the better (two gets you a fix of limited value, 3 that coincide nicely tell you it is likely a good fix, 4 will give you an idea which line is to be ignored if one is out, etc), in the few minutes that twilight allows. You do the same process at the evening twilight. You maintain a dead reckoning position during the day and take sun sights, say every hour, advancing the lines of position along your course by the distance covered to produce a series of running fixes through the day. A noon shot, gets you your latitude. If you happen to have a moon during the day, you can get actual two body fixes. In cloud or darkness though, you depend on dead reckoning or any other method you have available.
This is a good article, but I wonder if something along these lines would improve it? At a minimum, I think the referenced sentence should be deleted. As a latecomer to this fine article though, I thought it might be better to post this first.
KenWalker | Talk 07:33, 6 August 2006 (UTC)
[edit] "Celestial navigation...was the first system devised to help sailors cross the featureless oceans without having to rely on random chance to enable them to strike land."
Actually, no. A sailor can drop a line to the bottom to find its depth and character (muddy, sandy...). He can look for clouds (which form differently over land than over water) or land birds. And he can use dead reckoning. I think the article should rather emphasize that celestial navigation was the first accurate method that can be used anywhere in the world. Jrvz 11:04, 8 August 2006 (UTC)
[edit] Merge of Celestial Navigation Trainer into Celestial Navigation
I'm qualified in Celestial Navigation aboard both aircraft and watercraft, for both magnetic and grid navigation. I concur. Mugaliens 20:00, 28 September 2006 (UTC)
[edit] are these 57 stars visible to the naked eye?
Yes, but some are faint, and cannot be seen if the Moon is bright. Modern sextants multiply the illumination slightly through optics. - Mugs 18:41, 10 January 2007 (UTC)
[edit] Text Removed
I removed the following text for two reasons: "Sights on the moon, planets and stars allow navigation to occur when clouds obscure other objects." Reasons: First, if clouds are obscuring objects on the surface of the planet, they're usually obscuring celestial objects, as well! Second, celestial navigation is not normally performed in the vicinity of other landmarks due to it's lack of accuracy. Rather, those landmarks are used, instead. - Mugs 18:41, 10 January 2007 (UTC)
[edit] "Beyond the scope of this article"
Why is this statement here? "the size and location of this circular line of position can be determined using mathematical or graphical methods that are beyond the scope of this article." Why is it "beyond the scope of this article?" Wiki contains thousands of far more technical articles than celestial navigation! The methods are sufficently discussed in the remainder of the article. Text removed. - Mugs 18:44, 10 January 2007 (UTC)
[edit] Common practise today
"Modern practical navigators nearly always use celestial navigation in combination with satellite navigation to correct a dead-reckoning track, that is, a course estimated from a vessel's position, angle and speed."
My current experience at sea aboard oceangoing ships indicates this should read something like "With widespread availability of GPS, celestial navigation serves two primary function today. First is the determination of compass error in the absence of terrestial references. Secondly, celestial navigation is used as a check on the reliability of GPS positioning data." --Captclbecker 03:02, 29 January 2007 (UTC)
