Talk:Sextant

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[edit] Astrolabe link

Given the context of the intro paragraph, would it be more appropriate to link to Mariner's astrolabe, instead of to astrolabe. Not that I'm an expert on this, but the sextant, in the navigational context mentioned, was the direct replacement of the sailing tool, as opposed to the standard astrolabe, which was not well-suited for shipboard use. -- Palironsat 12:22, 30 August 2007 (UTC)

One problem is this is an oversimplification of the history of nav instruments. A very short list in order of invention would be something like:
Given that the mariner's astrolabe was pretty much out of use by the late 17thc, the octant/sextant replaced the Davis quadrant, at least in the Royal Navy. —Preceding unsigned comment added by Michael Daly (talk • contribs) 05:43, 12 September 2007 (UTC)

[edit] A question

I have a question:

If one is to measure the height of the horizon above the imagined sea level, can you do that with a sextant?

I imagine it should be possible with something on the sextant to keep it totally horizontal.

Sverdrup 13:06, 21 Nov 2003 (UTC)

If you can't see the horizon, an artificial horizon can used. You can also do this if you are far above the horizon. For aircraft, bubble sextants have been used. A traditional artificial horizon is a small box with a glass cover (looks like a little house with a glass roof) and has a pool of mercury in it. The mercury acts as a mirror and twice the angle to a star (or sun) is measured; the angle, being reflected, is twice the distance from the horizon. Michael Daly 04:59, 10 September 2007 (UTC)
I should add that if you don't know your height above the horizon, there is no general means of measuring the altitude with a sextant that I've ever heard of. An altimeter or independent means of determining altitude is required. Michael Daly 05:06, 11 September 2007 (UTC)

I removed extraneous information about damaged sextants, storing them, why someone shouldn't buy one without a case, etc. This is an encyclopedia article, not a product-buying guide. Alcarillo 17:20 27 Apr 2004 (UTC)

Given the age of the technology, and the amount of ones that can be found for sale at collectors and antique stores, information on how to identify the age, and condition of a sextant sounds like something that should be included at least somewhere. How it works and how to care for them is part of the information of a sextant that is just as valuable as what it does.--Talroth 23:48, 4 January 2007 (UTC)

[edit] Octant link

This article has a link to octant, which re-directs here. Anything on what to do with the link?? 66.245.121.70 02:18, 1 Dec 2004 (UTC)

The link to quadrant goes to a disam page, with no link to a relevant page. 68.1.98.64 04:01, 11 December 2006 (UTC)

[edit] Pilotage, horizontal angles etc

A sextant is not exclusively used to measure angles between a celestial object and the horizon. As many sailors know, it is also used to measure angles between two landmarks by placing it horizontaly. This can be very helpful in determining one's position at sea in coastal navigation, if one has a Chart, of course. --Jprats

You can also use it (the normal way up) to measure distance-off by measuring the angular height of an object like a lighthouse (if the real height is known and corrections are made for the current height of the tide). I've been wondering whether to put these ideas into here or into Pilotage. We can do something here about these present day, modern uses of the sextant in pilotage, as well as as a backup for the day when the GPS system or your own GPS receiver(s) pack up while you're at sea. It's not just a historical novelty. --Nigelj 11:26, 6 August 2005 (UTC)

[edit] Sextant

[edit] when?

Okay, I was doing a research project and I was just trying to figure out what time period sectants were used. I can't find it. It says something about 1730, but is that when they were used. I read somewhere about the Elizabethan era. Ahhh, I don't know anything about them. jess523s 23:34, 30 April 2006 (UTC)

[edit] Approximate vs. Precise

The reason I changed "precise location" to "approximate location" is that the use of a Line of Position (LOP) from a sextant reading is approximate, and the LOP from dead reckoning is likewise approximate. Stating "precise position" is implying something a little more specific. Generally, if you can establish your position within 1-3 miles of actual position you're doing pretty good. (unsigned comment by User:Quartermaster)

I changed it to just plain "fix". All fixes are approximate. A sextant fix might be good to a couple of miles, a GPS fix to a few yards, but they're both approximate. Calling something "precise" is almost meaningless unless you specify the numeric uncertainty. -- RoySmith (talk) 19:08, 21 May 2006 (UTC)

The question is now do we use the appropriate and relevant jargon "location fix" without linking to an explanation that all fixes are approximate. We're agreed that a celestial LOP and dead reckoning position are not precise. No position is precise, but a fix determined by celestial navigation within 1 mile is considered excellent, hence, the overriding need to delete the term "precise" here, which has been done.

How about a change that states "The intersection of that circle with a dead reckoning track, or another sighting yields a location fix (approximate location)." That way we use the appropriate vocabulary for the topic (location fix) but parenthetically clarify it to the casual Wikipedia user. Ideally, we would point to an entry explaining "location fix," but at least the "See also" links to celestial navigation and navigation would clarify things for the thorough and curious. Quartermaster.

[edit] illustrations

I think that this article could use some diagramatic illustrations elxplaining the layout and principle of a sextants operation. ike9898 04:10, 28 October 2006 (UTC)

  • I agree. I took out the photo I recently put up of my own sextant and substituted a diagram found in Wikimedia commons. There are other images there as well. KenWalker | Talk 16:12, 28 October 2006 (UTC)

[edit] Inventor?

This article seems to be saying that Newton developed the sextant. Is it not true that Newton was born 1643 and Tycho Brahe was using sextants in the mid 1500s? ::Obstructio 02:19, 23 March 2007 (UTC)

[edit] Confusion over sextants - two types - direct and reflecting

There are two different instruments referred to as sextants. One is a reflecting instrument, the other is not.

The sextant referred to in the intro as being invented in 995 is a mural sextant. This is not a reflecting instrument and is not anything like the sort of thing discussed in the majority of the article. Ditto Brahe's instrument - that was a direct reading sextant - a span of 60° gave a reading range of 60°. These things should have a separate section or a separate article.

Reflecting sextants derive from the octant - aka reflecting quadrant - and are the sort of instrument most think of today when they hear the word sextant. Reflecting instruments read up to 120° from an arc that spans 60° Michael Daly 05:06, 10 September 2007 (UTC)

I've created a new page for the non-reflecting sextant and removed from this page information on non-reflectig instruments. I have added a note to the top directing readers to the other page if they are interested in the other topic. Michael Daly 16:45, 13 September 2007 (UTC)

[edit] Astronomical Sextant is not a precursor to the Navigator's sextant.

The reason I created a new page for the astronomical sextant is that it is a completely different instrument. The astronomical sextant is not a precursor. The precursor to the sextant was the octant, and before that the reflecting quadrant. The astronomical sextant is just an angle measuring instrument with a single arc that happens to be 1/6 of a circle. Michael Daly 03:03, 20 September 2007 (UTC)

[edit] Bris sextant is not a sextant

Since the Bris sextant is not a true sextant, I wonder if it should be on this page or on it's own page as a navigation instrument. A link from this page under "see also" would be appropriate. Michael Daly 22:58, 27 September 2007 (UTC)