{ "export": { "source": "https://urth.darkrealm.vip/thread/whorl/483", "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": 483, "subject": "Double planets", "messages": 3, "voices": 3, "first": "1998-07-09T22:09:43+00:00", "last": "1998-07-13T13:00:38+00:00" }, "messages": [ { "message_id": "", "from": { "name": "mary whalen", "address": "marewhalen at yahoo.com" }, "date": "1998-07-09T22:09:43+00:00", "subject": "(whorl) Double planets", "in_reply_to": null, "reply_link": null, "blocks": [ { "kind": "text", "depth": 0, "text": "This is Sean Whalen (prion).\n\nAs I looked over the Whorl archives, it seemed to me that not everyone\nagreed that the planets Blue and Green were part of a double planet\nsystem, but were instead both in separate orbits around the sun. I\nthink their are many reasons to think that they're a double-planet\nsystem.\n\nHyacinth is described in the text as pointing towards Blue and Green\nand asking if Auk is going to one of those. She points just once, and\nit seems unlikely that two separate planets would happen to be close\nenough together for this at just that time.\n\nAlso, the inhumi fly between the two when they're in conjugation. \nIt's unlikely that they can fly in a vacuum, they probably have to\nbreathe. They also would have no way to fly in a vacuum with nothing\nto beat their arms against. If they used technology to get their,\nthey should be able to do this at other times as well. If they are\ntogether, at conjugation they could have an airbridge between them at\na certain time and not others if they have an elliptical orbit about a\ncommon center.\n\nThe fact that they're close in an elliptical orbit also would show why\nthey cause tidal waves and earthquakes in conjugation. If they are in\nseparate orbits, they would not be anywhere near enough to cause\nsignificant or noticeable seismic activity (not even the very-close\nMoon does anything to Earth, so it would almost have to be a very\nclose double system to have more of an effect than we experience with\nour large and near neighbor).\n\nThe fact that Green rises as seen on Blue and appears almost as bright\nas a second sun also shows how big and recognizable it must be,\nindicating nearness. Green would have to be impossibly close if it\nhad a different orbit to look that bright, not to mention that it's\nunlikely to rise on the particular night that Horn finishes his book;\nbut a double-planet would have a much greater chance of rising on any\nrandom night.\n\nAlso, it's probable that the Whorl is parked in one of the Lagrange\npoints of Blue and Green, where their mutual gravitational attraction\non it cancel each other out, and it remains at rest with no power\nbeing needed to maintain orbit. Otherwise, it's unlikely Horn would\nbe able to pick it out among all the other stars unless it was always\nvisible and near. It could be always visible because it's orbiting\nBlue, but it wouldn't be, because it took three days on the course\ntoward Blue for it to become obvious that that was their destination. \nIf the Whorld were in orbit, it would be apparent immediately. If it\nweren't in a Lagrange point, it would be very unlikely for an inhumu\nto pass in front of it while flying, as Horn seems to think occurs.\n\nprion" } ] }, { "message_id": "", "from": { "name": "Peter Westlake", "address": "peter at harlequin.co.uk" }, "date": "1998-07-13T12:37:46+00:00", "subject": "Re: (whorl) Double planets", "in_reply_to": "", "reply_link": "subject", "blocks": [ { "kind": "quote", "depth": 1, "text": "At 22:09 1998-07-09 -0700, prion wrote:\nAlso, it's probable that the Whorl is parked in one of the Lagrange\npoints of Blue and Green, where their mutual gravitational attraction\non it cancel each other out, and it remains at rest with no power\nbeing needed to maintain orbit. Otherwise, it's unlikely Horn would\nbe able to pick it out among all the other stars unless it was always\nvisible and near. It could be always visible because it's orbiting\nBlue, but it wouldn't be, because it took three days on the course\ntoward Blue for it to become obvious that that was their destination. \nIf the Whorld were in orbit, it would be apparent immediately. If it\nweren't in a Lagrange point, it would be very unlikely for an inhumu\nto pass in front of it while flying, as Horn seems to think occurs." }, { "kind": "text", "depth": 0, "text": "Unfortunately, I don't think Blue and Green *have* a Lagrange point.\nHal Clement has a short story called \"A Little Knowledge\", in which\na fleeing criminal parks his spaceship what he fondly imagines is\na Lagrangian point of a double star. But the two stars are too closely\nmatched in mass for it to work: one mass has to be considerably bigger\nthan the other. (If anyone has the story, and the ratio is 25.8 : 1,\nthen I shall appear very clever; if it isn't, well, how can I be expected\nto remember a detail like that?) The story ends with the fugitive\nfinally getting round to looking out of the window, to find himself\nplunging into one of the stars as it orbits towards him.\n\nWhatever the masses of Blue and Green may be, it isn't very likely\nthat they could differ enough to have Lagrangian points while both\nbeing reasonable places to go and live.\n\nSBear." } ] }, { "message_id": "", "from": { "name": "Alastair Reynolds", "address": "areynold at estsa2.estec.esa.nl" }, "date": "1998-07-13T13:00:38+00:00", "subject": "Re: (whorl) Double planets", "in_reply_to": "", "reply_link": "subject", "blocks": [ { "kind": "text", "depth": 0, "text": "Peter:" }, { "kind": "quote", "depth": 1, "text": "Unfortunately, I don't think Blue and Green *have* a Lagrange point.\nHal Clement has a short story called \"A Little Knowledge\", in which\na fleeing criminal parks his spaceship what he fondly imagines is\na Lagrangian point of a double star. But the two stars are too closely\nmatched in mass for it to work: one mass has to be considerably bigger\nthan the other. (If anyone has the story, and the ratio is 25.8 : 1,\nthen I shall appear very clever; if it isn't, well, how can I be expected\nto remember a detail like that?) The story ends with the fugitive\nfinally getting round to looking out of the window, to find himself\nplunging into one of the stars as it orbits towards him." }, { "kind": "text", "depth": 0, "text": "actually, any two orbiting point masses will always have five lagrangian \npoints around them; the one between them (exactly in the middle for equal \nmasses) is L1. L1 isn't stable - something placed at L1 only needs a \ntiny nudge in either direction and off it goes. \n\nThe point HC might have been making is that L4 or L5 (the \"usual\" Lagrange \npoints, off to either side) might only be stable if the ratio is as above?\n\nblimey - the first thing on the list I've responded to in ages!\n\nal" } ] } ] }