Wikipedia:Reference desk/Archives/Mathematics/2021 December 4

= December 4 =

What's the way to know what country is located 180 degrees from some specific city of another country?
What's the way to know what country is located 180 degrees from some specific city of another country? --ThePupil (talk) 00:05, 4 December 2021 (UTC)


 * By 180 degrees, I assume you mean "directly opposite" (as in, if you theoretically were able to go through the core of the earth). Those places are called antipodes and there are online tools for finding them, though mathematically you could negate the latitude and subtract/add 180 from the longitude (depending on which hemisphere you're in). For example, Perth is at roughly -32,116, and its antipode is at roughly 32,-64. ev iolite   (talk)  00:28, 4 December 2021 (UTC)
 * Antipodes_LAEA_inverted.png
 * Linguistic peeve &mdash; the alleged word antipode is a barbarism. The word antipodes is both singular and plural.
 * The singular back-formation antipode has become sanctioned by being so commonly used. If you are etymologically strict, singular antipodes is equally a solecism; Ancient Greek ἀντίποδες (antípodes) is strictly a plural noun, the plural of ἀντίπους (antípous). I have no qualms with pistachio and its pronunciation either, although this is spelled pistacchio in Italian and pronounced (pi-STAAH-kyoh).  --Lambiam 11:20, 4 December 2021 (UTC)
 * Antipodes means "opposite feet". If you're standing at the antipodes from me, your feet (of which you have two) are opposite to mine, so I don't see a problem.  I think antipode is clearly substandard; it's on a par with matrice or ephemeride or bicep &mdash; note that the last one is also very commonly used, but our biceps article correctly avoids it.  The biceps is a single muscle with two heads, which is what the word means. --Trovatore (talk) 20:46, 4 December 2021 (UTC)
 * But I wouldn't write, "My esteemed opponent's feet (of which they have two, last time I counted them) is opposite mine." My beef is with the use of antipodes as a singular noun. In Ancient Greek, your ἀντίπους is someone having their feet opposite of you. Ancient Greek ἀντίποδες refers to a plurality of such counterfooters. --Lambiam 23:41, 4 December 2021 (UTC)
 * Antipodes in English is a singular (and also plural) noun, just as is biceps. I hope you wouldn't write bicep in an encyclopedic context?  I agree it could have happened that we had adopted antipus as the singular, but we didn't.  I don't agree at all that "antipode has become sanctioned by being so commonly used"; that's just not true. --Trovatore (talk) 18:36, 5 December 2021 (UTC)
 * In Latin, biceps is singular, a nominalized adjective: "the two-headed one (viz. muscle)". The Latin plural is bicipites. Many muscles have medical names that are nominalized Latin adjectives, such as the longissimus. --Lambiam 22:01, 5 December 2021 (UTC)
 * It remains the case that antipodes has long standing as the singular and plural form in English. On the other hand antipode looks terrible, as plural-to-singular back-formations generally do.  Maybe a hundred years from now it will be unremarkable (like pea from pease), but for now it still comes across as informal or substandard usage. --Trovatore (talk) 22:05, 5 December 2021 (UTC)
 * Singular antipode was not invented yesterday either; it's almost as old as pea:, , .  --Lambiam 22:57, 5 December 2021 (UTC)
 * Let's not forget specie and (ugh!) indice and matrice. --  Jack of Oz   [pleasantries]  20:11, 9 December 2021 (UTC)
 * The form specie may be claimed to come from the Latin ablative. But even the permissive Wiktionary flags sapien as not only proscribed but also "best avoided". --Lambiam 23:58, 9 December 2021 (UTC)
 * Let's also not forget etymological fallacy. Language does not have to work the way it used to.  Language as it is used today may be used differently than it was in the past, that doesn't make it wrong.  Different is not a synonym for wrong.  -- Jayron 32 20:18, 9 December 2021 (UTC)
 * It so happens that if you match up the globe with the reflected globe, you'll see that land mostly matches up with water. The antipodes of Los Angeles, for example, is in the Indian Ocean, hundreds of miles from land, and the closest land is some tiny island in the French Southern and Antarctic Lands.  You can easily find the exceptions in the map to the right.  Some of Argentina and Chile matching up with China/Mongolia, some of the rest of South America with Southeast Asia, New Zealand and Spain, some Pacific islands with Africa. --Trovatore (talk) 01:02, 4 December 2021 (UTC)


 * Using Eviolite's recipe, we find that the antipode of the Kaʿbah at 21.4225°N, 39.8262°E is at 21.4225°S, 140.1738°W (140.1738° = 180° − 39.8262°) in the southern Pacific Ocean, about 50 km (30 mi) from from the Tematagi atol; see also . I suppose a Muslim performing salah right there could use any direction as the direction of prayer. --Lambiam 11:39, 4 December 2021 (UTC)

Geometric shape for four (or more) cylinders around a central cylinder
I am sure it has a specific name that was linked somewhere on discussions of the Energia (rocket) but I can't find it again. JoJo Eumerus mobile (main talk) 20:56, 4 December 2021 (UTC)
 * Quincunx? Rojomoke (talk) 06:27, 5 December 2021 (UTC)
 * The term "quincunx pattern" is used for the arrangement of the rocket engines in the S-IC and S-II, two stages of the Saturn V. --Lambiam 07:07, 5 December 2021 (UTC)
 * Yes, exactly that! JoJo Eumerus mobile (main talk) 21:31, 5 December 2021 (UTC)