| --- Log opened Sun Oct 21 00:00:09 2018 |
| 00:20 | | Emmy [Emmy@Nightstar-9p7hb1.direct-adsl.nl] has joined #code |
| 00:37 | | Emmy [Emmy@Nightstar-9p7hb1.direct-adsl.nl] has quit [Connection reset by peer] |
| 00:37 | | Emmy [Emmy@Nightstar-9p7hb1.direct-adsl.nl] has joined #code |
| 01:10 | | Emmy [Emmy@Nightstar-9p7hb1.direct-adsl.nl] has quit [Connection reset by peer] |
| 01:24 | | McMartin [mcmartin@Nightstar-rpcdbf.sntcca.sbcglobal.net] has quit [Operation timed out] |
| 01:24 | | McMartin [mcmartin@Nightstar-rpcdbf.sntcca.sbcglobal.net] has joined #code |
| 01:24 | | mode/#code [+ao McMartin McMartin] by ChanServ |
| 05:14 | | Derakon is now known as Derakon[AFK] |
| 05:34 | | celticminstrel is now known as celmin|sleep |
| 06:27 | <~Vornicus> | what'd I do |
| 06:28 | <~Vornicus> | oh shit spherical geometry |
| 06:32 | <&McMartin> | Question asked, question answered |
| 06:56 | | McMartin [mcmartin@Nightstar-rpcdbf.sntcca.sbcglobal.net] has quit [[NS] Quit: yay doom] |
| 06:57 | | McMartin [mcmartin@Nightstar-rpcdbf.sntcca.sbcglobal.net] has joined #code |
| 06:57 | | mode/#code [+ao McMartin McMartin] by ChanServ |
| 08:48 | | gnolam_ [lenin@Nightstar-ggccfi.cust.bahnhof.se] has joined #code |
| 08:52 | | gnolam [lenin@Nightstar-6ob4nc.cust.bahnhof.se] has quit [Ping timeout: 121 seconds] |
| 10:45 | | Emmy [Emmy@Nightstar-9p7hb1.direct-adsl.nl] has joined #code |
| 10:58 | | Emmy [Emmy@Nightstar-9p7hb1.direct-adsl.nl] has quit [[NS] Quit: Leaving] |
| 10:59 | | Emmy [Emmy@Nightstar-9p7hb1.direct-adsl.nl] has joined #code |
| 11:00 | | Kindamoody[zZz] is now known as Kindamoody |
| 12:21 | | Kindamoody [Kindamoody@Nightstar-bmuvn2.mobileonline.telia.com] has quit [[NS] Quit: Later!] |
| 12:42 | | gnolam_ is now known as gnolam |
| 12:42 | | mode/#code [+o gnolam] by ChanServ |
| 13:21 | | gnolam_ [lenin@Nightstar-ggccfi.cust.bahnhof.se] has joined #code |
| 13:24 | | gnolam [lenin@Nightstar-ggccfi.cust.bahnhof.se] has quit [Ping timeout: 121 seconds] |
| 14:14 | | gnolam_ is now known as gnolam |
| 14:14 | | mode/#code [+o gnolam] by ChanServ |
| 14:58 | | Degi [Degi@Nightstar-s2ncdu.dyn.telefonica.de] has joined #code |
| 15:15 | <@celmin|sleep> | XD |
| 15:16 | | celmin|sleep is now known as celticminstrel |
| 15:20 | <~Vornicus> | ah you have returned |
| 15:20 | <~Vornicus> | what's the dilly yo |
| 15:24 | <@celticminstrel> | Basically I have a geocentric setting and need to figure out how the sun moves in a way that a) produces a day-night cycle (this one's trivial, of course), b) gets light to the entire geosphere, and c) produces some seasonal changes. |
| 15:24 | <~Vornicus> | Oh that's easy |
| 15:25 | <@celticminstrel> | Well that's good to hear. |
| 15:25 | <@celticminstrel> | (FTR, B is a problem because the sun is not vastly larger than the geosphere. It might even be smaller.) |
| 15:28 | < ErikMesoy> | Foist off seasonal changes on the sun dimming and brightening in cycles? |
| 15:28 | <~Vornicus> | 1. the earth is spinning. 2. the sun has a period of 1 year |
| 15:28 | <~Vornicus> | And an inclined orbit. |
| 15:29 | <@celticminstrel> | Okay so the rotation of the geosphere creates the day-night cycle and the sun's movement produces the seasons... |
| 15:30 | <@celticminstrel> | I think I did consider what ErikMesoy said too actually, but this might work better... |
| 15:37 | <~Vornicus> | Dead easy. Sun orbits earth at 2.1 gigameters, has a radius of... 9.6 megameters (...is in fact 1.5x radius of earth in this system, but we pretend it's much less massive) |
| 15:38 | <~Vornicus> | Earth is earth sized and earth massed. |
| 15:38 | <~Vornicus> | The sun will appear to be the same visual size as sol is at the same distance |
| 15:38 | <~Vornicus> | er |
| 15:38 | <~Vornicus> | ...you know what I mean |
| 15:40 | <@celticminstrel> | These numbers seem awfully specific. |
| 15:41 | <~Vornicus> | I'm choosing the sun's numbers so that they give a sun that orbits a regular sized earth at a distance that would give it an orbit period of 1 earth year |
| 15:41 | <~Vornicus> | and that makes it the same visual size as the actual sun at actual sun distance |
| 15:43 | <@celticminstrel> | I see. Did you have a formula I could plug numbers into? |
| 15:43 | <~Vornicus> | Kepler's Third Law! |
| 15:43 | <@celticminstrel> | ...makes sense, heh. |
| 15:44 | <~Vornicus> | for two objects orbiting the same body, period^2/semimajor axis^3 is constant |
| 15:44 | <~Vornicus> | ...sorry, mean distance, which is different |
| 15:44 | <@celticminstrel> | ? |
| 15:45 | <~Vornicus> | semimajor axis is the ... median distance, sort of - it's periapsis + apoapsis. |
| 15:45 | <@celticminstrel> | Okay, so the semimajor axis is the 2.1 Gm? And where'd you get the radius from? |
| 15:45 | <~Vornicus> | But orbiting bodies spend far more time near the apoapsis, so that increases the mean distance |
| 15:46 | <~Vornicus> | I got the radius by making it proportionally sized with the actual sun |
| 15:47 | <~Vornicus> | 700 megameters / 150 gigameters * 2.1 gigameters |
| 15:48 | <@celticminstrel> | What are those first two numbers? |
| 15:48 | <~Vornicus> | equatorial radius of sun, distance of sun from earth |
| 15:50 | <@celticminstrel> | Googling the radius of the Earth seems to give more like 6.3 Mm... |
| 15:50 | <@celticminstrel> | Anyway, I think I should be able to use this. |
| 15:55 | <@celticminstrel> | Hmm, perod^2/semimajor^3 is constant but do I need to know what that constant is? |
| 15:56 | <~Vornicus> | If you've got a body of known period and mean distance then you can calculate it, but if you're just generating a new body with known period or distance you don't technically need to |
| 15:57 | <@celticminstrel> | So I can use it to figure out the moon's orbit once I have the sun's worked out but I don't need it to figure out the sun's orbit. |
| 15:58 | <~Vornicus> | sort of, right. I'm using the actual moon's numbers for calculating the fictional sun's |
| 15:58 | <@celticminstrel> | That seems like it gives me multiple choices for the sun's semimajor axis? |
| 15:58 | <@celticminstrel> | Ah, I see. |
| 15:58 | <~Vornicus> | Also, again this isn't semimajor axis |
| 15:59 | <@celticminstrel> | Wikipedia is wrong? |
| 15:59 | <~Vornicus> | oh weird, it is semimajor axis |
| 15:59 | <~Vornicus> | This is surprising to me! |
| 16:01 | <~Vornicus> | (but you can calculate your constant using the universal gravitational constant and the mass of the combined system... but, uh...) |
| 16:01 | <~Vornicus> | (we call attempts to calculate the universal gravitational constant "Weighing The Earth" for a reason) |
| 17:20 | | Kindamoody|autojoin [Kindamoody@Nightstar-ha9vck.mobileonline.telia.com] has joined #code |
| 17:20 | | mode/#code [+o Kindamoody|autojoin] by ChanServ |
| 17:22 | | Kindamoody|autojoin is now known as Kindamoody |
| 17:46 | <@gnolam> | Darnit. |
| 17:46 | | * gnolam is now tempted to rewatch the "Testing Geocentrism" series. |
| 17:56 | | Kindamoody [Kindamoody@Nightstar-ha9vck.mobileonline.telia.com] has quit [Connection reset by peer] |
| 18:01 | <@celticminstrel> | ? |
| 18:01 | | Kindamoody [Kindamoody@Nightstar-eubaqc.tbcn.telia.com] has joined #code |
| 18:01 | | mode/#code [+o Kindamoody] by ChanServ |
| 20:01 | <@celticminstrel> | Just checking, but... is "express X as a percentage of Y" equivalent to "X รท Y" or am I missing something? |
| 20:02 | <@celticminstrel> | (Well, and multiply by 100 to get a percentage instead of a fraction.) |
| 20:02 | <&McMartin> | You're not missing anything. The fact that division is what does this is why those numbers are called "rationals" |
| 20:02 | <&McMartin> | They're built out of ratios. |
| 20:03 | <@celticminstrel> | So I don't need the relative change formula for this then. |
| 20:03 | <@celticminstrel> | For some reason I thought I did at first. |
| 20:17 | | Derakon[AFK] is now known as Derakon |
| 20:24 | <@gnolam> | celticminstrel: Youtube series making fun of geocentrists (which, yes, are still a thing). Under all the snark, it's actually surprisingly educational. |
| 20:25 | <@celticminstrel> | When did geocentrists truly begin to be a thing, I wonder. |
| 20:25 | <@celticminstrel> | Middle Ages? |
| 20:25 | <&McMartin> | Ancient Greece? |
| 20:25 | <&McMartin> | Like, making heliocentrism actually *work* required Rennaissance-grade optics, AIUI |
| 20:25 | <@celticminstrel> | I don't remember. I do remember heliocentrism was thought up in Ancient Greece though. |
| 20:25 | <&McMartin> | That one didn't work though |
| 20:25 | <@celticminstrel> | Who was the epicycles guy again... Ptolemy? |
| 20:25 | <&McMartin> | Yes |
| 20:26 | <~Vornicus> | Epicycles, frankly, Worked |
| 20:26 | <&McMartin> | But Copernicus's version needed epicycles too |
| 20:26 | <&McMartin> | Yeah. |
| 20:26 | <@celticminstrel> | There was also Anaxagoras but I don't recall if his view was actually heliocentric. |
| 20:26 | <~Vornicus> | they didn't have enough math to make it Not Epicycles yet |
| 20:26 | <&McMartin> | They also didn't have enough Optics, or enough Science, IIRC |
| 20:26 | <&McMartin> | The problem with Heliocentrism is that if you measure the Sun from the Earth it is impossibly far away |
| 20:29 | <@celticminstrel> | Impossibly? |
| 20:29 | <~Vornicus> | To get one arc second of parallax on the sun you need to get measurements 700km apart |
| 20:29 | <~Vornicus> | ...simultaneous |
| 20:31 | <&McMartin> | So yeah |
| 20:32 | <&McMartin> | Basically until Kepler the issue wasn't so much We Were Too Dumb To Not Geocentrism but more Heliocentrism Wasn't Matching Our Observations |
| 20:32 | <@celticminstrel> | I have no idea how far 700km even is. |
| 20:32 | <&McMartin> | 2.2km/mi, so about 300 miles. |
| 20:33 | <@celticminstrel> | Yeah I don't know how far 300mi is either. |
| 20:33 | <~Vornicus> | 1.6 |
| 20:33 | <~Vornicus> | 2.2 lb/kg |
| 20:33 | <@celticminstrel> | It's not a question of units, it's a question of... how do you say this? |
| 20:34 | <&McMartin> | Er, yes, right, argh |
| 20:34 | <@celticminstrel> | Basically what I need is an example of something that's 700km long or two things that are 700km apart or something like that. |
| 20:35 | <&McMartin> | 500 miles, then, not 300 |
| 20:35 | <&McMartin> | So that's about the distance between San Francisco and San Diego |
| 20:37 | | * celticminstrel wonders what the horizon distance is... |
| 20:37 | <@celticminstrel> | Ah, two orders of magnitude smaller near sea level. |
| 20:38 | <@celticminstrel> | And doesn't reach 700km even atop Mount Everest, so yeah, I guess that would pose a major problem to the ancient Greeks. |
| 20:41 | < ErikMesoy> | yeah, helicentrism had major problems with the evidence |
| 20:42 | < ErikMesoy> | "If the Earth were moving back and forth as you describe, we should see parallax in the stars. We don't. Ergo, the Earth is stationary, QED." |
| 20:42 | <~Vornicus> | The closest star is over 1 parsec away, so you have to have *really* good instruments to do that |
| 20:42 | <&McMartin> | Halo effects are bad news |
| 20:42 | < ErikMesoy> | oh, there's a fascinating second layer to that |
| 20:43 | < ErikMesoy> | Some early astronomers speculated "What if the stars are really, really, really, REALLY far away and the parallax is just too small to measure..." |
| 20:43 | < ErikMesoy> | and then did the calculations, looked at angular width of stars in early telescopes, and calculated "...that would imply every single star is larger than Earth's orbit. Nah, can't be." |
| 20:44 | <&McMartin> | And that's why you prefer having your telescope in space |
| 20:46 | < ErikMesoy> | Space is one factor, the Airy disc is another (stock style telescopes exaggerate angular width) |
| 20:55 | | mode/#code [+o ErikMesoy] by ChanServ |
| 21:05 | <@ErikMesoy> | Semi-related to heliocentrism/geocentrism was the question of whether or not the Earth was rotating, which bumped into some of the same measurement precision issues: If the Earth is rotating, a dropped ball should deflect eastwards, which it only does by a *minute* amount. |
| 21:07 | <@ErikMesoy> | More practical application: if the Earth is rotating, cannonballs fired east should behave differently from ones fired south which again behave differently from ones fired west, and as the Royal Artillery Corps will be happy to tell you from a century of practical experience, they don't. |
| 21:08 | <@ErikMesoy> | Good luck arguing with the Royal Artillery Corps that their cannons shouldn't work. :P |
| 21:08 | <@ErikMesoy> | Isaac Newton also helped explain what was going on there with gravity and inertia... |
| 21:18 | | * McMartin learns about the existence of docs.gl, which is about a million times better than the docs on khronos.org |
| 21:58 | | himi [sjjf@Nightstar-v37cpe.internode.on.net] has quit [Ping timeout: 121 seconds] |
| 21:59 | <~Vornicus> | modern artillery calculations take into account the rotation of the earth |
| 22:07 | < Emmy> | they did that during WW1 already |
| 22:07 | <@gnolam> | For regular artillery it's not necessary to correct for the Coriolis effect. |
| 22:08 | <@gnolam> | It's only at /extreme/ ranges where it becomes something you actually have to worry about. |
| 22:10 | <@gnolam> | A modern ballistic computer will of course take it into account - because why not? - but it's not actually necessary to do. |
| 22:10 | <@celticminstrel> | How extreme are we talking? |
| 22:15 | <@ErikMesoy> | Vornicus: when I said "century of practical experience" I was trying to imply that this was after the Royal Artillery's _first_ century of existence, apparently that did not come across clearly |
| 22:15 | | Emmy [Emmy@Nightstar-9p7hb1.direct-adsl.nl] has quit [Ping timeout: 121 seconds] |
| 22:15 | <@ErikMesoy> | Modern artillery calculations take it into account, not so the ones at the time when geocentrism and rotation of earth were still serious matters of contention. |
| 23:03 | | VirusJTG [VirusJTG@Nightstar-42s.jso.104.208.IP] has quit [[NS] Quit: Leaving] |
| 23:44 | | Vornicus [Vorn@ServerAdministrator.Nightstar.Net] has quit [Ping timeout: 121 seconds] |
| --- Log closed Mon Oct 22 00:00:11 2018 |