{
  "export": {
    "source": "https://urth.darkrealm.vip/thread/whorl/807",
    "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": "whorl",
  "thread": {
    "id": 807,
    "subject": "Freakier Orbits",
    "messages": 1,
    "voices": 1,
    "first": "2000-04-05T10:08:32+00:00",
    "last": "2000-04-05T10:08:32+00:00"
  },
  "messages": [
    {
      "message_id": "<whorl-v0010-0299@digest.urth.net>",
      "from": {
        "name": "Adam Stephanides",
        "address": "adamsteph at earthlink.net"
      },
      "date": "2000-04-05T10:08:32+00:00",
      "subject": "(whorl) Re: Freakier Orbits",
      "in_reply_to": null,
      "reply_link": null,
      "blocks": [
        {
          "kind": "quote",
          "depth": 2,
          "text": "Kieran Mullen wrote:\nalga [actually, it was me] wrote:\n\nAnd if Green orbited Blue, and conjunction occurred only\nevery six years, that would mean that Green's orbital period around Blue\nwas six times as long as Blue's around the Short Sun, which I doubt\nwould be possible."
        },
        {
          "kind": "quote",
          "depth": 1,
          "text": "   I don't think that is correct.  Imagine two cars circling a race track.  If\none catches the other every six laps, then that means it is going 7/6 (1.16)\ntimes as fast.  If one were 6 times the speed of the other, it would pass it 6\ntimes or so in one year."
        },
        {
          "kind": "text",
          "depth": 0,
          "text": "Read what I wrote again.  My reference to Green's period being six times\nas long applied to the case in which Green orbited Blue (or Green and\nBlue orbited each other) while Blue orbited the Short Sun. "
        },
        {
          "kind": "quote",
          "depth": 1,
          "text": "mantis wrote:\nLately I've been thinking along the lines of those freaky orbits of\nSaturn's moons Janus and Epithemis  (sparked into posting this by the refs\nto shepherd moons).  Took me a few minutes just now, but I found a clean\nand easy reference:\n\n'Co-orbiting satellites are another weird example of a resonance.  Saturn's\ntiny moons Janus and Epithemis nearly share an orbit; but one never passes\nthe other.  They're forever going faster and slower in the orbit,\napproaching as though to pass a baton in a relay, only to drop back before\ngetting close enough to touch.  As seen from Saturn, they'd get closer,\nslow down, and then separate again as though they'd \"bounced off\" each\nother.  Things would look even more bizarre from one of the moons\nthemselves; you'd see the other moon approaching, but you'd slow down and\nit would speed up as you got closer, until finally it would flee out of\nsight.  Then the whole pattern would repeat half an orbit later--but you'd\nhave to go around to the other side of the satellite to watch it again.'"
        },
        {
          "kind": "text",
          "depth": 0,
          "text": "Stop the presses!  While searching the web for a statement of Kepler's\nThird Law, I stumbled across the asteroid 3753 Cruithne.  This\nasteroid's motion with respect to Earth is like that of Janus and\nEpithemis with respect to each other, but more complicated.  To really\nunderstand it, you have to go to the asteroid's web page\n(aries.phys.yorku.ca/~wiegert/3753.html) and look at the diagrams there;\nbut to quote the brief summary there: \"there are two types of motion\ngoing on: 1) every year, the asteroid traces out a kidney bean, 2) over\ntime, this kidney bean drifts along the Earth's orbit, tracing out a\nspiral which, when complete (after 385 years) fills in an overlapping\nhorseshoe.\"  Something like this, suitably jiggereda, could take care\nboth of the observed (see below) six-year frequency of conjunctions and\nof Green's visible movement across the sky at conjunction.  Cruithne's\norbit was described in a paper published in the June 12, 1997 _Nature_,\nin time for Wolfe to incorporate the information into OBW; and simpler\n\"spiral horseshoe\" orbits had been theoretically known before this,\nthough none had been observed.\n\nGiven the existence of \"freaky orbits\" like this, it's clear that\nuntutored individuals like me are unqualified to speculate as to what\norbital configurations might be stable.  But this does bring up two more\ngeneral issues (which had actually occurred to me before):\n\n1) Horn has only been on Blue for about twenty years, and so has only\nobserved three conjunctions.  Given this, do we know that the\nconjunctions occur every six years?  What I mean is that when Cruithne's\n\"kidney bean\" is at its closest to Earth, conjunctions take place every\nyear, but as it draws away, there is a long period when conjunctions\ndon't take place, following which they resume on the \"opposite side\" of\nEarth's orbit.  Something like this would be consistent with Horn's\nobservations.  If so, it would be good news for the inhabitants of Blue.\n\n2) Even if setting aside the question of Green's motion with respect to\nthe stars, it's clear that configurations allowing two planets to\nconjoin every six years (or every six years-pause-six years, as above)\nare rare.  That being so, it would be stupefyingly improbable if the\n_Whorl_ had ended up, purely by chance, at a system in which there are\ntwo habitable planets in such a configuration (let alone in which one of\nthe planets is populated by vampires who can fly across space at\nconjunction). So far I've come up with three alternatives to such a\nmind-boggling improbability:\n\nA) Typhon knew about the Blue-Green configuration (though not about the\ninhumi, as has already been established) and for some\nmegalomaniacal-tyrant reason deliberately chose to plant his colony on\nsuch a system.  (Possibly to facilitate his colonists' future conquest\nof the companion planet; but if so, why was it made so difficult to use\nthe landers to travel between Blue and Green?)\n\nB) The inhumi diverted the ship in midflight, as has already been\nhypothesized.  (But if so, why didn't they reprogram the ship's computer\nto land on Green while they were at it, instead of giving it a choice?)\n\nC) The Hierogrammates diverted the ship to Blue, to punish Typhon for\nhis presumption and the inhabitants of the _Whorl_ for their idolatry,\nor for some other cosmically incomprehensible reason. <g>\n\n--Adam\n\n*This is WHORL, for discussion of Gene Wolfe's Book of the Long Sun."
        }
      ]
    }
  ]
}