Talk:Mariner's astrolabe

Disputable claims?

I took this out of the page:

A precursor to the mariner's astrolabe was the navigational astrolabe developed by Muslim navigators during the early Middle Ages, which employed the use of a polar projection system for navigational purposes.^[1] In Europe, the elimination of the unnecessary parts of the Muslim navigational astrolabe eventually led to the development of the mariner's astrolabe.^[2]

^ Robert Hannah (1997). "The Mapping of the Heavens by Peter Whitfield", Imago Mundi 49, p. 161-162.
^ Allan Ferguson, Natural Philosophy through the Eighteenth Century and Allied Topics. (cf. T. Volume (1973), Annals of Science 30 (4), p. 457-464 (8).)

The first link is a circular reference - this article points to Islamic astronomy#Navigational astrolabe, which in turn just points back to this article. No info added and no explanation of what a navigational astrolabe is.

The claim that navigational astrolabe represents a precursor is questionable. The origins of the instrument are not well documented and those who have investigated (e.g. Daumas) point to the planispheric astrolabe as a precursor as stated in the article below the addition. I have no access to the second reference, so I can't verify what it says (in spite of being in one of the largest urban agglomerations in North America, no local library has it - I'd have to go through interlibrary loans or JStor, either of which is a biggish project for me right now). I'd like to know what Ferguson actually has to say that is relevant before putting the above text back in. Ferguson doesn't show up in any bibliography in the scientific instrument texts I have on hand, so I'm inclined to believe Daumas. Michael Daly 19:56, 16 October 2007 (UTC)[reply]

I changed this section:

==Limitations==

The mariner's astrolabe could not be used to determine the longitude (and therefore the exact position) of the observer.

It's slightly misleading because longtitude is obtained by taking into account the Greenwich time of the reading and then referring to empheris tables. However, time can determined by observing the positions predictable solar objects such as the moon or stars, which the Astrolabe cannot do. But if the observer had a clock handy then and Astrolabe could be used to determine longitude. Of course at the time the astrolabe was in use, the longtitude problem had not be solved so these instruments weren't used for that.

I have changed the section to this:

==Limitations==

The mariner's astrolabe needed to be suspended perpendicularly in order to measure the angle of the celestial object relative to itself. This meant it could not be used in windy conditions or rough seas. It also meant that it could not be used measure the angle between two objects, as which was necessary for the first longitude calculations later. Another limitation was that the instrument's angular accuracy was directly proportional to the length of an alidade, which was not very long.

. — Preceding unsigned comment added by Jason210 (talk • contribs) 21:01, 24 February 2011 (UTC)[reply]

"Stratocaster" not a navigational device?

It appears that a reference was made to a navigational tool called a "Stratocaster". I cannot find any evidence that this is anything but a marketing name for Fender Guitars, which built upon the name "Telecaster" and has no other significance. Would suggest removal of the reference. Since I have no expertise in the subject, I did not want to make the edit. Petriedish81 (talk) 14:30, 17 May 2017 (UTC)[reply]

External links modified

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History: what is the oldest astrolabe?

In this section it says:

“In 1988, only 65 were known to exist.[8] (...) [4] The Corpus Christi Museum of Science and History in Texas, United States, contains the world's oldest mariner's astrolabes with a confirmed date of 1554,(...) [9] An astrolabe dated between 1495 and 1500 was discovered in the wreck of the Portuguese explorer Esmeralda off the coast of Oman in 2014.[10]”

The text gives 65 as the number of still existing old astrolabes in 1988, the 2017 BBC-article (about the sunken Esmeralda) gives 108 as the number catalogued ((...) “this is only the 108th to be confirmed catalogued. It is also the earliest known example by several decades.”). The Corpus Christi Museum in Texas used to contain the world's oldest but is this now no longer the case.

I changed the text accordingly.--Gerard1453 (talk) 17:47, 9 November 2017 (UTC)[reply]

External links modified

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Added archive https://web.archive.org/web/20121122134304/http://www.ancruzeiros.pt/anci-astrolabio.html to http://www.ancruzeiros.pt/anci-astrolabio.html

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Usage Section

Hello Fellow Wikipedians,

I have evaluated this article in part for a class on the history of science. I believe that the usage section can be fleshed out more with some details on how the Mariner's astrolabe is used. The introduction also refers to the astrolabe being called a "ring", yet nowhere else in the article does the justification for this name stand out.

Zach Lienemann (talk) 17:10, 25 September 2020 (UTC)[reply]

[1] Robert Hannah (1997). "The Mapping of the Heavens by Peter Whitfield", Imago Mundi 49, p. 161-162.

[2] Allan Ferguson, Natural Philosophy through the Eighteenth Century and Allied Topics. (cf. T. Volume (1973), Annals of Science 30 (4), p. 457-464 (8).)

[1]

[2]