Talk:Minute of arc
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- 1 Number of square arcminutes in a sphere
- 2 from original article, "Arc of Minute"
- 3 merge arcminute and arcsecond articles
- 4 other uses of arcminutes and arcseconds
- 5 Visual Acuity Under Cartography?
- 6 Right ascension in cartography
- 7 Incorrect formula?
- 8 This is incorrect?
- 9 Minute of arc is standard terminology in astronomy; arcseconds not really well-merged...
- 10 Minute of Arc, The band
- 11 Race Elapsed Time
- 12 Unit conversions valid
- 13 Merge
- 14 Error: Reason for "not SI"
- 15 Someone please fix the recursive self-linking
- 16 Shouldn't prad, etc., be defined in this article?
Number of square arcminutes in a sphere
There isn’t 148,510,800 square minutes in a sphere, if it isn’t a misquotation that is perhaps something that’s only valid for the Earth’s sky. Earth is not a perfect sphere. 2πr = 60·360 = 21,600 arcminutes, r = 21,600/2π, A = 4πr^2 = 4π·(466,560,000/4π^2) = 466,560,000/π ≈ 148,510,660.498 square arcminutes. I'm fixing it, but just if anyone disagrees for some reason (since there's a source and everything for the false info). User:DeclinedShadow 02:50, 17 July 2009 (UTC)
Rewrote this again since someone changed it back, and added some calculations. Anyone of you can just look at the Square degree page, there's the same formula being used. User:DeclinedShadow 03:52, 2 August 2009 (UTC)
from original article, "Arc of Minute"
What the heck is this feature for?? Well, I'll be darned. Shouldn't this be "Minute of Arc"?
- Yes, it should be "minute of arc" or "arcminute". But I would prefer an article on angular measure, where all such terms can be discussed in one place. Where did you find the link to "arc of minute"? --Zundark, 2001 Nov 2
- Nautical_mile is one link to here, Minute is another. What's an idea on cleaning this one up? Doesn't look like the angular measures are made, and I'm new and reluctant to attempt tying loose ends and botching it, or to start a new article that may not be warrented. I'm expecting this should fit with other standardized units of measure (linear distance, area, volume) in how it looks and behaves. Once created, perhaps this page ought to redirect to the 'cleaned up' version under Zundark's preferred title. Would an arc 'Orders of magnitude' be appropriate? Two ways to look at that one: 1) Arc minute of Earth (as standardized by the Nautical mile vs. the same on the Sun, and 2) Degree vs. Arc minute vs. Radian. If an old-hand at this doesn't mind steering me in an appropriate direction, I'll tack this on my 'Wiki-to-do' and fuss over it over time. --Romaq 2002 Jan 21
I'll see what I can do on anglar measurements. -- April 09:04 Aug 7, 2002 (PDT)
First we have to decide which is the "most correct". Arcsecond (or arc second) is far less awkward, anyway. --Elektron 10:28, 2004 Jul 4 (UTC)
- I find in practice (as an astronomer) that arcminute and arcsecond are most used. Certainly 'second of arc' is never used in my experience. Of course these things crop up in several fields. EddEdmondson 10:32, 4 Jul 2004 (UTC)
merge arcminute and arcsecond articles
I see above that there has been some discussion in the past about merging the articles on arcminute and arcsecond. This may be a good idea to pick up. Most info on one page could be (or already is) on the other. MHD 11:04, 3 February 2006 (UTC)
- For a comparison, centimetre redirects to metre, but millimetre redirects to 1 E-3 m. Is there a reason to keep both arcminute and arcsecond separate from degree (angle) as well? It might make sense to merge all three. Otherwise, merging a minimum of arcsec into arcmin makes sense to me. Should someone put up a "merge suggested" tag? --zandperl 04:49, 8 February 2006 (UTC)
I agree: merging all three may be a sensible thing to do, but maybe also a little more time consuming to do, as opposed to just merging the arcminute and arcsecond articles and leaving the degree article as it is.
As to the millimetre/centimetre/metre issue, I have no idea why millimetre links to 1 E-3 m, and not to metre, which it should, in my opinion.
MHD 09:56, 8 February 2006 (UTC)
- Nobody else seems to care, so I decided to finally start the merging process of arcsecond into this article. There are some information elements in the arcsecond article that I still have to merge into this one, after that is done (hopefully tomorrow), I will make arcsecond redirect to minute of arc. I will also merge the information from milliarcsecond into here. Cheers, MHD 21:09, 26 March 2006 (UTC)
- (anonymous user): this is an encyclopedia, not a dictionary. We don't need a new article for each prefix of a standard unit. Merge at will :)
- I support the merging of the arcminute and milliarcsecond articles, as long as no information from either article is lost/discarded. The content of the two articles is substantially different and the milliarcsecond article contains some interesting facts and trivia. User: Jaganath 16:12 07 June 2006 UTC
other uses of arcminutes and arcseconds
Arcminutes and arcseconds are indeed used when measuring the declination of an object on the sky. When measuring the right ascension (RA), these units are not used (as is correctly stated by User:Zandperl in the article). Instead, RA is measured in:
- hours, (24 h = 360 degrees -> 1 h = 15 degrees)
- minutes, (1 minute = 15/60 degrees = 1/4 of a degree = 15 arcminutes) and
- seconds, (1 second = 15/3600 degrees = 1/240 of a degree = 15 arcseconds)
This a fair thing to put in an article on arcminutes (or arcseconds for that matter).
However, there are numerous other coordinate systems that use the degree (and its subdivisions arcminute and arcsecond), such as Galactic coordinates, though it is also common to express galactic longitude and latitude in ordinary decimal fractions of degrees, the coordinates of an object may be expressed as "l = 48.85 and b = -1.96", meaning that it has a galactic longitude of 48 and 85/100 of a degree and a galactic latitude of minus 1 minus 96/100 of a degree.
Oops, forgot to sign this message yesterday. It was written by me: MHD 11:35, 4 February 2006 (UTC)
- I also threw the below into the article before, and some cleaned-up version might be appropriate in the article.
- Astronomers typically measure Right Ascension in hours, minutes, and seconds. RA minutes and seconds are not to be confused with Declination arcminutes and arcseconds, as they are of a different size.
- In right ascension and longitude, the size of the degree (and therefore arcmin and arcsec) changes with how far you are from the equator.
- As opposed to a degree of latitude, which always corresponds to about 111 km (69 mi), a degree of longitude corresponds to a distance from 0 to 111 km: it is 111 km times the cosine of the latitude, when the distance is laid out on a circle of constant latitude; if the shortest distance, on a great circle were used, the distance would be even a little less. (Longitude page)
- Whatever we decide upon should also have a modified version in the arcsecond page.
- --zandperl 15:12, 4 February 2006 (UTC)
I agree to the fact that information in the arcminute page should also be on arcsecond, that is exactly the reason why I proposed to merge these two articles (see topic above this one). 17:23, 4 February 2006 (UTC)
Visual Acuity Under Cartography?
Visual acuity should be under a different section as best as I can tell. Unfortuntately, I only know about visual acuity what I've read on Wikipedia. Should the section be called "Ophthalmology"? Thanks! Don 20:13, 19 February 2006 (UTC)
Right ascension in cartography
I am only familiar with the term 'Right Ascension' when it is used in astronomy. I am a bit confused as to what it really means in cartography: does it refer to a different concept than geographical longitude, or is is just a different name for the same thing? I understand that the distance over the surface of the earth corresponding to 1 degree of right ascension would vary depending on the geographical latitude (how far from the equator you are). Talking about such variations makes much less sense in astronomy, which is why I removed the reference to astronomy in the Cartography section.
In addition: the page about Right ascension does not handle the subject of its use in cartography at all, so I don't think it is wise to have a link pointing from the cartography section of Minute of arc directly to Right ascension.
Can somebody help me out on the meaning of 'right ascension' in cartography? And maybe (help me) come up with a clearer description in this section and/or write a section about the use of right ascension in the Right ascension article?
Thanks, MHD 12:18, 18 April 2006 (UTC)
Although I am not a firearm afficionado, i think the correct formula is 2*tan(MOA ∙ π/21600)*distance, since you are trying to find the opposite side of an angle, given the adjacent side. It may be that for accurate estimates, the tan is not needed since the results are very close, for example in the example given, the answer computed using tan is approximately 1.04719756 which differs by only 7∙10^-9 inches from the previous value.
I also think it's incorrect. Tangent is a right triangle function, in the main article formula, tan(MOA ∕ 60)*distance, tangent is being applied to an isosceles triangle. Because the two equal angles at the base approach 90 degrees (in these cases) the error is not so great. However, the correct approach is to split the isosceles triangle into two identical right triangles, as the person who posted the above paragraph did, calculate the value for the halves then multiply it by two. So the formula for would be 2*tan(MOA/120)*distance. (JohnMc 7-31-08) —Preceding unsigned comment added by JohnMc (talk • contribs) 00:10, 1 August 2008 (UTC)
This is incorrect?
How about adding a simple paragraph that discusses the "minute of arc" vs "minute of angle". While it looks to me like astronomer types use arc, the firearms people most definitely do not. So a firearms person coming to this page may be confused, even if arc is technically the correct term (which I am not sure of). So maybe a "common confusion" paragraph/section that explains common usages, etc. Arthurrh 19:57, 9 July 2007 (UTC)
Minute of arc is standard terminology in astronomy; arcseconds not really well-merged...
Re: the previous post -- "Minute of angle" may be the correct terminology in firearms work -- from the article, I gathered that -- but it is never used in astronomy. In astronomy, the correct terminology is "minute of arc". I don't have a reference for this, but I have long experience as a professional optical astronomer. So the moral is, don't be too hasty in categorically saying a term is not used, the world is very big!
Regarding the merging of arcsecond into arcminute, I think it could be improved. Also, there's no noting that the abbreviation "mas" means "milliarcsecond" in some contexts; if you look at e.g. the article on "Teegarden's star" the quoted values for parallax and proper motion make use of the "mas" notation, which directs you to "minute of arc", where there is no longer an explanation of the "mas". 188.8.131.52 = Jthorstensen ; 04:39, 29 April 2007 (UTC)
(A little later) -- I went ahead and touched up the arcsecond discussion a bit, in particular adding an explicit reference to the milliarcsecond; I know it's a standard SI prefix, but it seems to confuse people so it's worth a sentence or two. I can't seem to get my four-tilde signature to work from home, but I am JThorstensen.
Minute of Arc, The band
minute of arc the band can be found at www.mypace.com/moa
This appears at the head of this article as of 11:42PM EST. That belongs on a disambiguation page! Whomever posted that needs to take it down and do it right. Thanks. —Preceding unsigned comment added by 184.108.40.206 (talk) 03:44, 9 April 2009 (UTC)
Race Elapsed Time
In terms of racing, I've seen the elapsed time displayed as, say 33'21" (33 minutes, 21 seconds). However, this article is not very clear on what happens in races that last over an hour. Does the minutes continue to count up (93'=60'+33'), does it use the degree symbol °, or is it displayed in some other format?
I request a new section on the use of the arcminute in racing.
Christopher, Salem, OR (talk) 07:50, 1 July 2010 (UTC)
- This has nothing to do with racing or timing, Arcminutes are a measure of angle not time. — M3TA(info) @ 09:36, 29 August 2010 (UTC)
Unit conversions valid
I just checked all of the unit conversions using Google as a calculator both with Google's value of pi and with MathWorld's value of pi. The only value I was unable to verify to all digits was minute of arc in radians (which has one more significant figure than Google supports). Given that these conversions involve only integers and pi, I am shocked by this label on this article: "The factual accuracy of this article may be compromised by unit conversions quoted to a greater precision than can be justified from the original data. Please help improve this article by truncating values to a suitable number of significant figures." I haven't edited wikipedia in a while, so I am reluctant to remove this label. rs2 (talk) 20:35, 29 July 2010 (UTC)
- It probably shouldn't do that. These are two distinct things. Retitling to (say) "Minute of Angle (firearms)" and "Minute of Arc (geometry)" would help, with topnotes to the other on each page. htom (talk) 00:25, 19 October 2010 (UTC)
Error: Reason for "not SI"
Currently the article contains the statement: "However, they [arcsecond and arcminute] are not themselves SI units because they are dimensionless.". This looks false to me -- is there a reference for this? Regardless of whether one considers units of angle to be dimensionless, that does not preclude them from being SI units. They are presumably not SI units for some other reason, perhaps because instead SI chooses radian as the unit for angle. Gwideman (talk) 01:14, 8 June 2011 (UTC)
The article says "This article is about geometry. For firearms terminology, see Minute of Angle." When you click on "Minute of Angle", it brings you right back to this page, because "Minute of Angle" is set to redirect here. Something is obviously wrong...220.127.116.11 (talk) 04:17, 6 February 2012 (UTC)
Shouldn't prad, etc., be defined in this article?
I see prad, etc., used at least in the units-of-angle table to express various angle units in terms of other ones.
But nowhere in Wikipedia could I find "prad" per se. Googling, I learned that prad stands for picoradian, one-trillionth (10-12) of a radian. But even the term "picoradian" occurs only once in Wikipedia, and does not seem to be defined there.