Talk:Minute of arc

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[edit] 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)


It seems sensible that one of Minute of arc and Arcsecond should be renamed to fit in with the other. Both belong to Category: Units of angle Icairns 21:39, 25 Jun 2004 (UTC)

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)

[edit] 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

[edit] 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.
  1. 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.
  2. 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)

[edit] 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)

[edit] 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)

[edit] Incorrect formula?

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.

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