{"id":5324,"date":"2014-03-08T16:50:26","date_gmt":"2014-03-08T21:50:26","guid":{"rendered":"http:\/\/esr.ibiblio.org\/?p=5324"},"modified":"2014-03-08T16:51:13","modified_gmt":"2014-03-08T21:51:13","slug":"which-way-is-north-on-your-new-planet","status":"publish","type":"post","link":"http:\/\/esr.ibiblio.org\/?p=5324","title":{"rendered":"Which way is north on your new planet?"},"content":{"rendered":"<p>So, here you are in your starship, happily settling into orbit around an Earthlike world you intend to survey for colonization. You start mapping, and are immediately presented with a small but vexing question: which rotational pole should you designate as &#8216;North&#8217;?<\/p>\n<p>There are a surprisingly large number of ways one could answer this question.  I shall wander through them in this essay, which is really about the linguistic and emotive significance of compass-direction words as humans use them.  Then I shall suggest a pragmatic resolution.<\/p>\n<p><!--more--><\/p>\n<p>First and most obviously, there&#8217;s magnetic north.  Our assumption &#8216;the planet is Earthlike&#8217; entails a nice strong magnetic field to keep local carbon-based lifeforms from getting constantly mutated into B-movie monsters by incoming charged particles.  Magnetic north is probably going to be much closer to one pole than the other; we could call that &#8216;North&#8217;.<\/p>\n<p>Then there&#8217;s spin-axis north.  This is the assignment that makes north relate to the planet&#8217;s rotation the same way it does on Earth &#8211; that is, it implies the sun setting in the west rather than the east. Not necessarily the same as magnetic north; I don&#8217;t know of any reason to think planetary magnetic fields have a preferred relationship to the spin axis.<\/p>\n<p>Next, galactic north. Earth&#8217;s orbital plane is inclined about 26% from the rotational plane of the Milky Way, which defines the Galaxy&#8217;s spin-axis directions; these have been labeled &#8216;Galactic North&#8221; and &#8220;Galactic South&#8221; in accordance with the Earth rotational poles they most closely match.  On our new planet we could flip this around and define planetary North so it matches Galactic North.<\/p>\n<p>Finally there&#8217;s habitability north.  This one is fuzzier.  More than 3\/4ths of earth&#8217;s population lives in places where north is colder and south is warmer. We might want to choose &#8216;North&#8217; to preserve that relationship, which is embedded pretty deeply in the language and folklore of most of Earth&#8217;s cultures. Thus, &#8216;North&#8217; should be the hemisphere with the most habitable land.  (Or, if you&#8217;re taking a shorter-term view, the hemisphere in which you drop your first settlement.  But let&#8217;s ignore that complication for now.)<\/p>\n<p>If all four criteria coincide, happiness.  But how likely is that?  They&#8217;re probably distributed randomly with respect to each other, which means we&#8217;ll probably get perfect agreement on only one in every sixteen exoplanets.<\/p>\n<p>But not all these criteria are equally important.  Magnetic North really only matters to geophysicists and compass-makers.  Galactic North is probably interesting only to stargazers.<\/p>\n<p>I think we have a clear winner if spin-axis north coincides with habitability north.  This choice will preserve continuity of language pretty well.  If they&#8217;re opposite, and galactic north coincides with magnetic north, that&#8217;s a tiebreaker.  If the tiebreakers don&#8217;t settle it, I&#8217;d go with spin-axis north.  <\/p>\n<p>But reasonable people could differ on this.  Discuss; maybe we could submit a proposal to the IAU.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>So, here you are in your starship, happily settling into orbit around an Earthlike world you intend to survey for colonization. You start mapping, and are immediately presented with a small but vexing question: which rotational pole should you designate as &#8216;North&#8217;? There are a surprisingly large number of ways one could answer this question.&hellip; <a class=\"more-link\" href=\"http:\/\/esr.ibiblio.org\/?p=5324\">Continue reading <span class=\"screen-reader-text\">Which way is north on your new planet?<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[11,4],"tags":[],"class_list":["post-5324","post","type-post","status-publish","format-standard","hentry","category-science","category-science-fiction","entry"],"_links":{"self":[{"href":"http:\/\/esr.ibiblio.org\/index.php?rest_route=\/wp\/v2\/posts\/5324","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/esr.ibiblio.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/esr.ibiblio.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/esr.ibiblio.org\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"http:\/\/esr.ibiblio.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=5324"}],"version-history":[{"count":1,"href":"http:\/\/esr.ibiblio.org\/index.php?rest_route=\/wp\/v2\/posts\/5324\/revisions"}],"predecessor-version":[{"id":5325,"href":"http:\/\/esr.ibiblio.org\/index.php?rest_route=\/wp\/v2\/posts\/5324\/revisions\/5325"}],"wp:attachment":[{"href":"http:\/\/esr.ibiblio.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5324"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/esr.ibiblio.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5324"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/esr.ibiblio.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5324"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}