Talk:Prosthaphaeresis

A fact from Prosthaphaeresis appeared on Wikipedia's Main Page in the Did you know column on 8 May 2005. The text of the entry was as follows: Did you know... that the astronomer Tycho Brahe calculated products quickly using Prosthaphaeresis, a 17th century algorithm exploiting trigonometric identities? A record of the entry may be seen at Wikipedia:Did you know archive/2005/May.

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I'm pretty sure these are not any old charts that are here today and gone tomorrow, but rather ephemerides, on which Wikipedia has an excellent article. (Though the spell-checker on this talk page editor objects both to "ephemerides" and to "Wikipedia"!) D021317c 05:44, 8 September 2007 (UTC)Reply

This image was displayed and referenced to in the main article -- supposedly a slide rule based on prosthaphaeresis. In fact this slide rule is only based on similarity of triangles. It is nice, but unrelated. Maybe we should put this in a new articled called "triangle similarity" (that is currently just a subsection of "similarity").Scoskey (talk) 15:28, 11 November 2008 (UTC)Reply

You're sort of correct - there is such a thing as a slide rule based on prosthaphaeresis, and the reference describes it, but the image has nothing to do with it and was added at a later time. Dcoetzee 02:35, 12 November 2008 (UTC)Reply

Actually, the process that the reference describes is not related to prosthaphaeresis at all (and it is precisely what the image displays). The method and the slide rule that they use are solely based on the proportionality of similar triangles. If you read their method you will know it cannot be prosthaphaeresis since at no point is there any mention of ${\displaystyle \cos(\alpha +\beta )}$, etc. That is, adding angles is never done. Here is the reference in question, which we again removed.

http://findarticles.com/p/articles/mi_qa3950/is_200401/ai_n9372466

Again, this is an interesting type of slide rule, it just should be called something else and put on another page.

Scoskey (talk) 15:35, 18 November 2008 (UTC)Reply

Hmmm, point taken, you're right about that. It seems the authors are either being terribly subtle in the connection between their device and prosthaphaeresis, or they overgeneralized the term to include any trigonometric method. Dcoetzee 21:27, 18 November 2008 (UTC)Reply

Prosthaphaeresis has more than one meaning. In seventeenth century astronomy this was a term that denoted the angle, as viewed from the earth, between the position of the projection of the moon's position onto the ecliptic plane and the position of a virtual moon that moved in that plane with a constant angular velocity with respect to the earth. The calculation of this prosthaphaeresis was at the heart of pre-chronometer navigation. I think that the main article has confused these meanings. See Newton's forgotten lunar theory, by Nicholas Kollerstrom, published by the Green Lion Press. It seems that Newton spelt prosthaphaeresis with the first h missing. I don't know if this was a standard misspelling in his time. I think that Newton's Greek was rather shaky. Charles Leedham-Green [email protected] —Preceding unsigned comment added by 82.7.210.233 (talk) 14:49, 15 December 2009 (UTC)Reply

Can some commentary (or links) be added concerning whether this is still used in any modern applications? DKEdwards (talk) 18:23, 23 January 2022 (UTC)Reply