UmbralRaptop changed the topic of #principia to: READ THE FAQ: http://goo.gl/gMZF9H; The current version is Fano. We currently target 1.3.1, 1.4.x, 1.5.1, and 1.6.1. <scott_manley> anyone that doubts the wisdom of retrograde bop needs to get the hell out | https://xkcd.com/323/ | <egg> calculating the influence of lamont on Pluto is a bit silly…
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<discord-> D​RVeyl. — Sometimes I think they're just showing off.
<discord-> A​cer_Saccharum. — ^
<discord-> A​cer_Saccharum. — But I enjoy reading through it anyway
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<discord-> e​gg. — @Sir Mortimer well, once all the easy problems are done... https://twitter.com/bofh453/status/1137386068976836608
<kmath> <bofh453> <@eggleroy> we've done so many things in Principia that at this point we generate a new research problem every time we fart, basically.
<discord-> e​gg. — (doing persistent rotation correctly is actually a hard problem, which explains why PersistentRotation does it wrong)
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<discord-> L​ord Lima Bean. — hey guys
<discord-> L​ord Lima Bean. — a friend of mine got real expansion working with principia
<discord-> L​ord Lima Bean. — so
<discord-> L​ord Lima Bean. — that's a thing
<UmbralRaptor> real expansion - set Ω_Λ to 0.7?
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<discord-> L​ord Lima Bean. — will try to convince him to post the patch onto a site soon, if they want lol
<discord-> L​ord Lima Bean. — afk, going to slep now
<discord-> B​utcher. — How many PhDs between the Principia devs? Got to be well into double figures.
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<discord-> e​gg. — 0, I should get one someday
<discord-> B​utcher. — 😮
<discord-> B​utcher. — My world view is shattered.
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<discord-> e​gg. — I do have an MSc. in maths though
<discord-> S​ir Mortimer. — University degrees are wildly overrated.
<discord-> e​gg. — @Sir Mortimer heavily depends on what the subject is tbh; the CS degree madness is a bit special
<discord-> S​ir Mortimer. — Yep
<discord-> S​ir Mortimer. — But there is a point at which degrees turn into a conterindication for competence. At least in my line of work
<discord-> S​ir Mortimer. — And the local schools
<discord-> e​gg. — @Sir Mortimer again it all depends on what said line of work is and what the degrees are about
<discord-> e​gg. — While I did learn a lot of stuff (in numerical analysis/physics/astronomy/astrodynamics, but even a bit of pure maths) by working on Principia, the whole thing would have been utter chaos (and would probably never have started) if not for a solid theoretical basis from my maths degree; otoh said degree is utterly irrelevant for my job as a software engineer
<discord-> e​gg. — (I don't do numerics at work, if I did then it would obviously be relevant)
<discord-> S​tandecco. — so you have a degree in mathematics and work as a software engineer?
<discord-> S​tandecco. — that explains a lot of things
<discord-> e​gg. — yeah
<discord-> e​gg. — I work in internationalization, which either explains or more probably is explained by the linguistics nerdery
<discord-> S​tandecco. — definitely
<discord-> S​tandecco. — meanwhile I have to choose a major
<discord-> S​tandecco. — but I guess that if you went to work as a software engineer after a mathematics major, it's not that important?
<discord-> e​gg. — I did some programming on the side (including Principia), but yeah, I wouldn't say it's critical
<discord-> S​tandecco. — that's comforting, at least
<discord-> e​gg. — (I also know, e.g., someone who went from maths MSc to physics PhD to probably chemistry postdoc)
<discord-> S​tandecco. — I'm mostly between some variant of engineering and physics
<discord-> S​tandecco. — with a vague interest in coding
<discord-> S​tandecco. — math > physics > chemistry is quite the ride
<discord-> e​gg. — hm, I'm getting strange things for the semimajor axis
<discord-> B​utcher. — @Standecco I have a degree in chemistry and work in software.
<discord-> S​tandecco. — are you in europe? Just curious if there are any differences
<discord-> T​heRealWiwaxia. — 6 AM is real big brain hours
<discord-> e​gg. — reminder: the world is not flat
<discord-> e​gg. — it's quarter past noon here
<discord-> B​utcher. — @Standecco I am, I'm in the UK.
* discord- S​tandecco. — cough_
* discord- S​tandecco. — cough_
<discord-> e​gg. — :-p
<discord-> B​utcher. — @egg is CET so must be in Western Europe somewhere.
<discord-> S​tandecco. — CE
<discord-> B​utcher. — My first degree was supposed to be maths with comp sci, maths is hard. ☹
* discord- e​gg. — is in CH, also in FR regularly (e.g. last week)_
<discord-> T​heRealWiwaxia. — I'm thinking about Earth science...
<discord-> S​tandecco. — @Butcher I guess I don't need to care that much then
<discord-> S​tandecco. — that's good
<discord-> S​tandecco. — @egg working on that orbital elements tool?
<discord-> e​gg. — yeah
<discord-> e​gg. — @Standecco btw, bear in mind that physics involves rather a lot of maths (for perspeggtive, at ETHZ the first year is common between physicists and mathematicians, complete with intro physics classes for the mathematicians as well), so it is somewhat seamless to switch between the two early on (at ETHZ many people switch either way during 1st year)
<discord-> S​ir Mortimer. — Maths is common in pretty much any STEM field, except maybe chemistry but i might be mistaken
<discord-> T​heRealWiwaxia. — Chemistry has math too
<discord-> e​gg. — yeah, there's a lot of it
<discord-> e​gg. — something something quantum chemistry something
<discord-> S​ir Mortimer. — Why am i not surprised 😉
<discord-> T​heRealWiwaxia. — In fact all I hear from chemistry people is complaining about the math
<discord-> S​tandecco. — @egg oh, he switched on the first year?
<discord-> e​gg. — but it's only for physics that it gets literally fused with maths in the first year at ethz
<discord-> S​ir Mortimer. — All the stuff I had to take on... and most was promptly forgotten, never to be used again
<discord-> e​gg. — @Standecco nah, I know lots of people who switched first year, but the person in question did a maths msc, then a physics phd, so that's not a 1st year switch
<discord-> S​ir Mortimer. — But alas, that’s true for almost all the classes, not just maths
<discord-> e​gg. — @Sir Mortimer and now, orbit contracts dig up all the maths :D
<discord-> S​tandecco. — oh, a phd
<discord-> S​tandecco. — that's definitely a thing I aim for
<discord-> e​gg. — i should do one someday
<discord-> T​heRealWiwaxia. — phd papers though 😬
<discord-> S​tandecco. — @egg do you need one?
<discord-> e​gg. — @Standecco no, what does that have to do with anything :-p
<discord-> e​gg. — Provided that I find an interesting subject, this sounds like an interesting thing to do
<discord-> S​tandecco. — that's peculiar, for sure
<discord-> e​gg. — @Standecco no here's something actually peculiar:
<discord-> e​gg. — the mean semimajor axis of the TOPEX/Poseidon / Jason-1 .. 3 orbit is smaller than the lowest distance from the geocentre
<discord-> e​gg. — circular orbits are *weird*
<discord-> e​gg. — `One would expect more mathematical simplicity, rather than more complexity, for nearly circular orbits,`
<discord-> S​tandecco. — a= 7100km?
<discord-> S​tandecco. — a = 7100km? (edited)
<discord-> S​tandecco. — are those the orbital parameters of those satellites?
<discord-> S​tandecco. — are circular orbits weird just for their mathematical interpretation?
<discord-> S​tandecco. — I don't really get how the mean sma can be smaller than the perigee
<discord-> e​gg. — the altitude of very circular orbit is heavily perturbed by J2
<discord-> e​gg. — you get 2 perigees and 2 apogees per orbit
<discord-> S​tandecco. — how can there be 2? If the definition of perigee is "the point at which the distance from the geocentre is lowest", then only one of those perigees is actually the perigee
<discord-> e​gg. — so the mean elements (reasonably preserved quantities generalizing the Keplerian elements when the orbit is perturbed) are rather unrelated
<discord-> e​gg. — @Standecco well, you can get two that are equal
<discord-> e​gg. — but you generally just define that as local minima of distance from the centre
<discord-> e​gg. — because usually there's only one per revolution
<discord-> e​gg. — (and in fact you sort of *have* to say local, because then you run into the one of the next revolution)
<discord-> e​gg. — @Standecco see the graphs here: http://articles.adsabs.harvard.edu//full/1961AJ.....66..129I/0000131.000.html
<discord-> e​gg. — http://articles.adsabs.harvard.edu/cgi-bin/t2png?bg=%23FFFFFF&/seri/AJ.../0066/600/0000131.000&db_key=AST&bits=4&res=100&filetype=.gif
<discord-> e​gg. — hm discord doesn't want to show that image
<discord-> S​tandecco. — I saw the graphs but I don't really know how to read them
<discord-> e​gg. — it's altitude graphs along one revolution
<discord-> e​gg. — well, distance-from-geocentre, not altitude
<discord-> e​gg. — let's not bring the ellipsoid into this
<discord-> S​tandecco. — What is ω?
<discord-> e​gg. — argument of periapsis
<discord-> S​tandecco. — How does that work with 2 perigees?
<discord-> e​gg. — ω = 0: periapsis at the equator, ω = 90 degrees: periapsis at the north pole, 270: periapsis at the south pole
<discord-> e​gg. — @Standecco it's a theoretical argument of the periapsis; at this point these quantities are only distantly related to the actual geometry of your trajectory
<discord-> e​gg. — because that one is completely garbled by perturbations from J2
<discord-> S​tandecco. — Oh it's a polar orbit?
<discord-> K​obymaru. — Are they more meaningful for more eccentric orbits?
<discord-> e​gg. — @Standecco nah, it's not polar, I'm oversimplifying
<discord-> S​tandecco. — Oh ok
<discord-> e​gg. — @Kobymaru yeah it all starts coinciding with normal intuitions as soon as you're even a tiny bit eccentric
<discord-> S​tandecco. — Yeah I know what the argument of periapsis is, I didn't know ω was the symbol for it
<discord-> e​gg. — at e > 0.001 you're all good
<discord-> S​tandecco. — Does the inclination matter for this?
<discord-> e​gg. — it comes into the equations, but it doesn't fundamentally change matters
<discord-> e​gg. — (if it's 0 then things become more entertaining of course)
<discord-> S​tandecco. — That's what I was thinking of
<discord-> S​tandecco. — What happens at 0°?
<discord-> e​gg. — a different mess entirely
<discord-> e​gg. — but i is rarely very 0; e can for some satellite get small enough that you get in trouble like this (TOPEX/Poseidon and Jason are examples)
<discord-> S​tandecco. — So, trying to read the graphs
<discord-> S​tandecco. — The km axis is [+4;-4]
<discord-> S​tandecco. — Is that relative to the theoretical radius?
<discord-> e​gg. — yeah it's relative to some sort of mean value, the point here being the study of the variations
<discord-> e​gg. — these are *very* circular orbits
<discord-> S​tandecco. — And so the lowest points are the perigees we're looking for
<discord-> e​gg. — I made some similar graphs based on the equations in that paper https://imgur.com/a/1k0zEVc
<discord-> S​tandecco. — Then why at ω=0 the lowest point is not at 0° true anomaly?
<discord-> e​gg. — @Standecco because the perturbation from J2 dominates; the geometry of the underlying Kepler orbit is no longer visible at all
<discord-> e​gg. — ω is "where the perigee lives" only in the Keplerian world
<discord-> e​gg. — here you mainly get altitude variations from J2, not from your own eccentricity, so it's more and more drowned as e tends to 0
<discord-> e​gg. — (in my graphs 𝑢 is the argument of latitude, 𝛹 the geocentric latitude)
<discord-> S​tandecco. — So it's why at e=0 the function becomes a perfect cosine function?
<discord-> e​gg. — yup, and independent of ω
<discord-> e​gg. — because at e=0, ω has no effect on the Kepler orbit
<discord-> e​gg. — the only thing you see is perturbations, if the orbit were not perturbed you would see a lnie
<discord-> e​gg. — (in my graphs 𝑢 is the argument of latitude, 𝜓 the geocentric latitude) (edited)
<discord-> e​gg. — a line even
<discord-> e​gg. — a straight line that is
<discord-> e​gg. — of the horizontal kind
<discord-> S​tandecco. — Because r would be constant
<discord-> S​tandecco. — That's how it is in lko
<discord-> e​gg. — here you have variation in altitude as a function of latitude: https://i.imgur.com/GDIzVmQ.png
<discord-> e​gg. — (well, radius, not altitude, again let's not bring the geoid in there)
<discord-> e​gg. — note how at e=0 you just have a high spot at the equator, low spots at extremal latitudes; as e becomes higher it turns into something weird, until at the bottom at high e it's like the unperturbed Keplerian case, because the Keplerian distance variation dominates
<discord-> S​tandecco. — Wait I don't get this
<discord-> S​tandecco. — Why is it higher because of latitude?
<discord-> e​gg. — what is the word because doing here
<discord-> S​tandecco. — I don't know
<discord-> S​tandecco. — No I know
<discord-> e​gg. — this is just another way of drawing the same graph, with a different parameter
<discord-> S​tandecco. — So latitude is the equivalent of anomaly?
<discord-> e​gg. — the satellite goes twice per revolution over all latitudes between -i and +i
<discord-> S​tandecco. — Ok that's how I thought then
<discord-> S​tandecco. — But why is this so different than the previous ones?
<discord-> e​gg. — not really equivalent but the argument of latitude (which is ω + anomaly) can be turned into the latitude (backwards it's ambiguous because two passes)
<discord-> e​gg. — @Standecco it's folded upon itself in a sense, because the satellite passes twice over each latitude
<discord-> e​gg. — the argument of latitude (or the anomaly) is basically the same thing as time for these orbits
<discord-> e​gg. — but here you have latitude, which behaves differently: at high latitudes your latitude changes slower with respect to time, and then you go back in latitude
<discord-> S​tandecco. — And why is ω=90° so different?
<discord-> S​tandecco. — A straight line instead of that continuous curve
<discord-> e​gg. — it's the only ω where both passes (going north and going down) are at the same altitude
<discord-> e​gg. — ω = 270° would be the same
<discord-> e​gg. — take ω = 0°, perigee on the equator; as you go north, you go through your perigee; but as you go south, you go through the same latitudes backwards, but through your apogee
<discord-> e​gg. — at ω = 90°, crossing all latitudes takes you from perigee to apogee, and after that it's the same backwards
<discord-> S​tandecco. — And that's only relevant when eccentricity tales over
<discord-> S​tandecco. — At e=0, is the radius smallest at i and -i and biggest at the equator?
<discord-> S​tandecco. — And that's only relevant when eccentricity takes over (edited)
<discord-> e​gg. — yup
<discord-> e​gg. — > And that's only relevant when eccentricity takes over
<discord-> e​gg. — well, it holds everywhere though: you can see that ω = 90° is always a single line (curved at low e) whereas the others form these weird closed contours
<_whitenotifier-5dfc> [Principia] pleroy opened pull request #2218: Rewrite FukushimaEllipticJsMaclaurinSeries - https://git.io/fjwKz
<_whitenotifier-5dfc> [Principia] Pending. Build queued… - 
<_whitenotifier-5dfc> [Principia] Pending. Building… - http://casanova.westeurope.cloudapp.azure.com:8080/job/Principia/3701/
<_whitenotifier-5dfc> [Principia] eggrobin reviewed pull request #2218 commit - https://git.io/fjwKx
<_whitenotifier-5dfc> [Principia] eggrobin labeled pull request #2218: Rewrite FukushimaEllipticJsMaclaurinSeries - https://git.io/fjwKz
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<_whitenotifier-5dfc> [Principia] pleroy synchronize pull request #2218: Rewrite FukushimaEllipticJsMaclaurinSeries - https://git.io/fjwKz
<_whitenotifier-5dfc> [Principia] pleroy closed pull request #2218: Rewrite FukushimaEllipticJsMaclaurinSeries - https://git.io/fjwKz
<_whitenotifier-5dfc> [Principia] pleroy pushed 7 commits to master [+0/-0/±7] https://git.io/fjw6i
<_whitenotifier-5dfc> [Principia] pleroy 8ea5a52 - Start writing polynomials for Js.
<_whitenotifier-5dfc> [Principia] pleroy 1a978b0 - Polynomials in m.
<_whitenotifier-5dfc> [Principia] pleroy 3f1ecea - A complete implementation of Js, with poor names.
<_whitenotifier-5dfc> [Principia] ... and 4 more commits.
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<_whitenotifier-5dfc> [Principia] pleroy opened pull request #2219: Support for 16.2.0 preview 2.0 - https://git.io/fjwXf
<_whitenotifier-5dfc> [Principia] pleroy pushed 1 commit to master [+0/-0/±1] https://git.io/fjwXU
<_whitenotifier-5dfc> [Principia] pleroy 1cb675a - Preview 2.
<_whitenotifier-5dfc> [Principia] Pending. Build queued… - 
<_whitenotifier-5dfc> [Principia] Pending. Building… - http://casanova.westeurope.cloudapp.azure.com:8080/job/Principia/3702/
<_whitenotifier-5dfc> [Principia] eggrobin labeled pull request #2219: Support for 16.2.0 preview 2.0 - https://git.io/fjwXf
<_whitenotifier-5dfc> [Principia] pleroy synchronize pull request #2219: Support for 16.2.0 preview 2.0 - https://git.io/fjwXf
<_whitenotifier-5dfc> [Principia] Pending. Build queued… - 
<_whitenotifier-5dfc> [Principia] Failure. Build finished. - http://casanova.westeurope.cloudapp.azure.com:8080/job/Principia/3702/
<_whitenotifier-5dfc> [Principia] Pending. Building… - http://casanova.westeurope.cloudapp.azure.com:8080/job/Principia/3703/
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<discord-> S​tandecco. — it's weird because I would think the radius to be lowest at the equator and highest elsewhere
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<_whitenotifier-5dfc> [Principia] pleroy commented on pull request #2219: Support for 16.2.0 preview 2.0 - https://git.io/fjw1I
<_whitenotifier-5dfc> [Principia] Pending. Build queued… - 
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<_whitenotifier-5dfc> [Principia] Failure. Build finished. - http://casanova.westeurope.cloudapp.azure.com:8080/job/Principia/3704/
<_whitenotifier-5dfc> [Principia] pleroy synchronize pull request #2219: Support for 16.2.0 preview 2.0 - https://git.io/fjwXf
<_whitenotifier-5dfc> [Principia] Pending. Build queued… - 
<_whitenotifier-5dfc> [Principia] Pending. Building… - http://casanova.westeurope.cloudapp.azure.com:8080/job/Principia/3705/
<_whitenotifier-5dfc> [Principia] Success. Build finished. - http://casanova.westeurope.cloudapp.azure.com:8080/job/Principia/3705/
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<_whitenotifier-5dfc> [Principia] pleroy closed pull request #2219: Support for 16.2.0 preview 2.0 - https://git.io/fjwXf
<_whitenotifier-5dfc> [Principia] pleroy pushed 4 commits to master [+0/-0/±6] https://git.io/fjwyt
<_whitenotifier-5dfc> [Principia] pleroy 1eceec0 - Support for 16.2.0 preview 2.0.
<_whitenotifier-5dfc> [Principia] pleroy aaddefb - Update the scripts too.
<_whitenotifier-5dfc> [Principia] pleroy 0cabcf5 - Fix the coverage instrumenter.
<_whitenotifier-5dfc> [Principia] pleroy cb29831 - Merge pull request #2219 from pleroy/Preview2 Support for 16.2.0 preview 2.0
<_whitenotifier-5dfc> [Principia] pleroy opened pull request #2220: Rewrite JacobiSNCNDNReduced - https://git.io/fjwyG
<_whitenotifier-5dfc> [Principia] Pending. Build queued… - 
<_whitenotifier-5dfc> [Principia] Pending. Building… - http://casanova.westeurope.cloudapp.azure.com:8080/job/Principia/3706/
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<_whitenotifier-5dfc> [Principia] Failure. Build finished. - http://casanova.westeurope.cloudapp.azure.com:8080/job/Principia/3706/
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