{ "export": { "source": "https://urth.darkrealm.vip/thread/urth/3137", "note": "Exported from an unofficial mirror of a public mailing list. Copyright in each message remains with the person who wrote it. Email addresses are obscured as `user at host`, the form the original archive published. This file was rebuilt from parsed fields rather than retained headers, so it is faithful in content but not byte-exact.", "addresses": "obscured as 'user at host'" }, "archive": "urth", "thread": { "id": 3137, "subject": "distance", "messages": 6, "voices": 4, "first": "2002-04-10T04:29:13+00:00", "last": "2002-04-12T05:02:46+00:00" }, "messages": [ { "message_id": "", "from": { "name": "maa32", "address": "maa32 at dana.ucc.nau.edu" }, "date": "2002-04-10T04:29:13+00:00", "subject": "(urth) distance", "in_reply_to": null, "reply_link": null, "blocks": [ { "kind": "text", "depth": 0, "text": "Well, Blattid, since you put it so succinctly, the choice is easy. Of course \nthe 30,000 league figure is incorrect! Which means that Green might only \nfluctuate a tiny amount from its 80,000 league distance, which is where the \nmoon is in our day. Of course, this means that the inhumu have to fly a long \nway, but that's cool with me (after all, that tree ship can fly a long way, \ntoo - and I don't think they are much different).\n\nAnd this distance, closer to 80,000, wouldn't screw up the tides as much and \nwouldn't seem to be such a weird system; it might just fluctuate a little bit, \nlike a moon in a slightly unstable orbit due to recent gravitational \ndisturbances. In this case, a new sun coming. Sure, let's say that Green is \nat 60,000 leagues at conjunction, making it ... about the same size as Lune.\n\nThanks! You made everything so much easier! So we know that the moon was \nmoved from about 80 to 50 thousand leagues in Severians day ... a fluctuation \nof about 30 thousand leagues ... if a new gravitational vortex where to \ndisrupt this system, would the moon act like a gyroscope and oscillate in and \nout of orbit, first close and then far, between 60 and 100 thousand leagues, \nuntil it reached a stable orbit somewhere around 80,000? Like an old \nfashioned weight scale: you step on it, and then it goes back and forth until \nit reaches equilibrium, and equal distance on the up and down swing until \nthere is no perceptible movement.\n\nWould a new gravitational well induce this kind of alteration in an orbit? \nCould this continue for a long time, reducing a little bit over time? Also, \nlet's keep in mind that the moon is proportionally very large for a satellite \nwhen compared with the earth's mass. It is huge compared to the satellites of \nmost of the gas giants.\n\nI hereby gladly revoke my uncritical acceptance of 30,000 leagues. You guys \nwere so right; that figure sucks. That astronomer is one shady dude!\nThanks.\nMarc Aramini" } ] }, { "message_id": "", "from": { "name": "Dan'l Danehy-Oakes", "address": "ddanehy at siebel.com" }, "date": "2002-04-11T18:26:09+00:00", "subject": "RE: (urth) distance", "in_reply_to": "", "reply_link": "subject", "blocks": [ { "kind": "quote", "depth": 1, "text": "Well, Blattid, since you put it so succinctly, the choice is easy. Of\ncourse the 30,000 league figure is incorrect! Which means that Green\nmight only fluctuate a tiny amount from its 80,000 league distance, " }, { "kind": "text", "depth": 0, "text": "I'm no orbit mechanic, but that seems unlikely with a six-year period,\nand _very_ unlikely to cause the inhumi to be able to cross only for a \nshort period." }, { "kind": "quote", "depth": 1, "text": "Thanks! You made everything so much easier! " }, { "kind": "text", "depth": 0, "text": "Oh. Good." }, { "kind": "quote", "depth": 1, "text": "So we know that the moon was moved from about 80 to 50 thousand\nleagues in Severians day " }, { "kind": "text", "depth": 0, "text": "Ahem. We do not know that it \"was moved.\" I believe that most models\nsuggest that the Moon _will_ in fact move closer over (geological) \ntime." }, { "kind": "quote", "depth": 1, "text": "... the moon is proportionally very large for a satellite when compared\nwith the earth's mass. It is huge compared to the satellites of most\nof the gas giants." }, { "kind": "text", "depth": 0, "text": "Correct; we are actually best regarded as a double-planet system. (The\ncenter about which the Earth-Moon system mutually orbits is, if I am not \nmistaken, not actually inside the Earth.) " } ] }, { "message_id": "", "from": { "name": "Jerry Friedman", "address": "jerry_friedman at yahoo.com" }, "date": "2002-04-11T19:56:04+00:00", "subject": "RE: (urth) distance", "in_reply_to": "", "reply_link": "subject", "blocks": [ { "kind": "quote", "depth": 2, "text": "--- Dan'l Danehy-Oakes wrote:\nWell, Blattid, since you put it so succinctly, the choice is easy. Of\ncourse the 30,000 league figure is incorrect! Which means that Green\nmight only fluctuate a tiny amount from its 80,000 league distance, " }, { "kind": "quote", "depth": 1, "text": "I'm no orbit mechanic, but that seems unlikely with a six-year period,\nand _very_ unlikely to cause the inhumi to be able to cross only for a \nshort period." }, { "kind": "text", "depth": 0, "text": "I quite agree." }, { "kind": "quote", "depth": 2, "text": "Thanks! You made everything so much easier! " }, { "kind": "quote", "depth": 1, "text": "Oh. Good." }, { "kind": "quote", "depth": 2, "text": "So we know that the moon was moved from about 80 to 50 thousand\nleagues in Severians day " }, { "kind": "quote", "depth": 1, "text": "Ahem. We do not know that it \"was moved.\" I believe that most models\nsuggest that the Moon _will_ in fact move closer over (geological) \ntime." }, { "kind": "text", "depth": 0, "text": "Not that I've ever heard. See for example\n,\n, and with the\nleast detail but the greatest appearance of reliability,\n. I think it's\nextremely unlikely that our moon turned into Severian's Lune on its\nown." }, { "kind": "quote", "depth": 2, "text": "... the moon is proportionally very large for a satellite when\ncompared\nwith the earth's mass. It is huge compared to the satellites of most\nof the gas giants." }, { "kind": "quote", "depth": 1, "text": "Correct; we are actually best regarded as a double-planet system. (The\ncenter about which the Earth-Moon system mutually orbits is, if I am not\n\nmistaken, not actually inside the Earth.) " }, { "kind": "text", "depth": 0, "text": "Not quite. The formula for the position of the center of mass is\nx_cm = (m_moon x_moon + m_earth x_earth) / (m_moon + m_earth), where\nx's are positions and m's are masses. If we let x_earth be 0 and\nuse the radius of the moon's orbit for x_moon, we find the center\nof mass to be about 4620 km from the center of the earth, less than\nthe radius of the earth, which is about 6380 km.\n\nJerry Friedman" } ] }, { "message_id": "", "from": { "name": "Jerry Friedman", "address": "jerry_friedman at yahoo.com" }, "date": "2002-04-11T20:44:52+00:00", "subject": "Re: (urth) distance", "in_reply_to": "", "reply_link": "subject", "blocks": [ { "kind": "text", "depth": 0, "text": "--- maa32 wrote:\n..." }, { "kind": "quote", "depth": 1, "text": "Thanks! You made everything so much easier! So we know that the moon\nwas \nmoved from about 80 to 50 thousand leagues in Severians day ... a\nfluctuation \nof about 30 thousand leagues ... if a new gravitational vortex where to \ndisrupt this system, would the moon act like a gyroscope and oscillate\nin and \nout of orbit, first close and then far, between 60 and 100 thousand\nleagues, \nuntil it reached a stable orbit somewhere around 80,000?" }, { "kind": "text", "depth": 0, "text": "The only possible orbits, once the disrupting force has stopped, are\nthe familiar ellipses and the parabolic and hyperbolic escape orbits." }, { "kind": "quote", "depth": 1, "text": "Like an old \nfashioned weight scale: you step on it, and then it goes back and forth\nuntil \nit reaches equilibrium, and equal distance on the up and down swing\nuntil \nthere is no perceptible movement." }, { "kind": "text", "depth": 0, "text": "Gravity doesn't work that way (unless there are other forces, like\nthose of a spring or a string)." }, { "kind": "quote", "depth": 1, "text": "Would a new gravitational well induce this kind of alteration in an\norbit? " }, { "kind": "text", "depth": 0, "text": "Nope." }, { "kind": "quote", "depth": 1, "text": "Could this continue for a long time, reducing a little bit over time? " }, { "kind": "text", "depth": 0, "text": "Nope. Sorry to be so negative, but I really don't see how the Blue-\nGreen system can work the way Wolfe sketchily describes it, unless\nthere's some weird solution to the three-body problem that I don't\nknow about. Or unless the planets have something like giant rocket\nengines on them or a very long cable between them. (Aha! Now we\nknow how the inhumi cross!)\n...\n\nJerry Friedman" } ] }, { "message_id": "", "from": { "name": "Dan'l Danehy-Oakes", "address": "ddanehy at siebel.com" }, "date": "2002-04-11T21:11:20+00:00", "subject": "RE: (urth) distance", "in_reply_to": "", "reply_link": "subject", "blocks": [ { "kind": "text", "depth": 0, "text": "Jerry -- Hey, I said I'm no orbital mechanic!\n\nI remembered that the E/M system orbited a mutual center which wasn't\nthe center of the Earth; obviously I was a bit off about where it was.\n\nAs for the Moon getting closer to the Earth, well, that's just stuff\nI remember from like 1960s LIFE magazines..." } ] }, { "message_id": "", "from": { "name": "Jeff Wilson", "address": "jwilson at io.com" }, "date": "2002-04-12T05:02:46+00:00", "subject": "RE: (urth) distance", "in_reply_to": "", "reply_link": "subject", "blocks": [ { "kind": "quote", "depth": 1, "text": " From: " }, { "kind": "text", "depth": 0, "text": " \"Dan'l Danehy-Oakes\"