raptop changed the topic of #principia to: READ THE FAQ: http://goo.gl/gMZF9H; The current version is Fréchet. We currently target 1.5.1, 1.6.1, and 1.7.x. <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… | <egg> also 4e16 m * 2^-52 is uncomfortably large
<discord-_> e​gg. — order 0 means something like what you have on the left here
<discord-_> e​gg. — so imagine a selenopotential turned on a lathe
<discord-_> P​teropodidae. — Ah
<discord-_> e​gg. — dependent on latitude, but not longitude
<discord-_> e​gg. — if you look at the graphs, you can see that on the 10-year graph the degree 50 order 0 one has the same kind of behaviour as degree 50 order 50
<discord-_> e​gg. — but on the one-month graph it stays in the same place where the other one dances around
<discord-_> e​gg. — because over the course of the repeat ground track cycle, the orbit will see different longitudes which will do different things to it, which will not happen on a rotationally symmetric selenopotential
<discord-_> e​gg. — but in the long run this averages out over a cycle, so long-term trends are more similar
<discord-_> e​gg. — J3 tells you how egg-shaped things are :-p
<discord-_> e​gg. — 🥚
<discord-_> P​teropodidae. — Ah, so that's what J2 means
<discord-_> P​teropodidae. — Sorry, it'll take a bit for me to digest this
<discord-_> P​teropodidae. — Everything comes back to an egg pun sooner rather than later, doesn't it 😛
<discord-_> e​gg. — Eggsactly
<discord-_> e​gg. — This is not bad (though for gravitation you would use positive m always, and have C and S coefficients for m > 0, which are handled with negative m there) https://iaem.at/Members/zotter/spherical_soundfield/sh_vib.gif
<discord-_> e​gg. — C20 is another way to talk about J2
<discord-_> e​gg. — You will hear about C22/S22 in here when trying to get GEO satellites to stay put
<discord-_> P​teropodidae. — Those are higher-order harmonics which are important for those orbits?
<discord-_> e​gg. — yeah, n=m means zonal, so variations solely in longitude rather than solely in latitude for m=0
<discord-_> e​gg. — so this tells you how much your GEO sat gets pulled east or west
<discord-_> P​teropodidae. — Sorry, jumping back and forth to make sure I'm actually understanding what you're saying
<discord-_> P​teropodidae. — Is this the right equation in which C, S, n, and m are used?
<discord-_> A​cer_Saccharum. — correct me if I'm wrong, to form a true ellipsoid from these you would need a sum of infinite even-degree order 0 harmonics, right?
<discord-_> A​cer_Saccharum. — not that you'd use an ellipse to model the gravity of a very oblate body
<_whitenotifier-d13c> [Principia] eggrobin commented on issue #2556: Disable timewarp rotation if under a certain threshold - https://git.io/JfGuk
<discord-_> e​gg. — yeah an ellipsoid has infinitely many J2n terms
<discord-_> e​gg. — > not that you'd use an ellipse to model the gravity of a very oblate body
<discord-_> e​gg. — An ellipse is actually a very nice thing; you generally express things as perturbations from that
<discord-_> e​gg. — actually I have some plots lying around somewhere
<discord-_> A​cer_Saccharum. — well a rotating ellipsoid does have an equipotential congruent with the mean ellipsoid of the body, but that potential is a sum of gravitational and centrifugal potentials
<discord-_> A​cer_Saccharum. — well a rotating ellipsoid does have an equipotential surface congruent with the mean ellipsoid of the body, but that potential is a sum of gravitational and centrifugal potentials (edited)
<discord-_> A​cer_Saccharum. — the actual gravitational equipotential aren't ellipses as far as I know
<discord-_> P​teropodidae. — > yeah, n=m means zonal, so variations solely in longitude rather than solely in latitude for m=0
<discord-_> P​teropodidae. — Did you mean sectoral here?
<discord-_> e​gg. — possibly not, but since you show deviation from some reference (in order for things not to be dominated by the oblateness) it doesn’t matter if you subtract the centrifugal potential on both sides  :D
<discord-_> e​gg. — @Pteropodidae yes
<discord-_> e​gg. — Ah the aptly named `C20 is not the ellipsoid.png`
<discord-_> e​gg. — C20 and C40 give you something that is pretty close to the ellipsoid though
<discord-_> P​teropodidae. — Ah, ok, that makes sense
<discord-_> e​gg. — @Pteropodidae I recommend this paper https://twitter.com/eggleroy/status/1061617686344536064
<kmath> <eggleroy> Franz Barthelmes (2013), Definition of functionals of the geopotential and their calculation from spherical harmoni… https://t.co/uMM3lNlMPM
<discord-_> P​teropodidae. — And just in time; I was just about to ask a question that that paper would probably have answered
<discord-_> e​gg. — Also, pretty picture https://twitter.com/eggleroy/status/1046455246015418368
<kmath> <eggleroy> Gravity disturbance¹ of the Combined Gravity Model GGM05C² to degree and order 𝑁 with respect to GRS80, on the GRS8… https://t.co/GXmLnlboiK
<discord-_> A​cer_Saccharum. — is it known why there's a large low gravity anomaly at the southern tip of india?
<discord-_> P​teropodidae. — Thank you for coming back and taking the time to answer my questions, egg!
<discord-_> P​teropodidae. — I really appreciate it
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<_whitenotifier-d13c> [Principia] rsparkyc commented on issue #2556: Disable timewarp rotation if under a certain threshold - https://git.io/JfGg5
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<discord-_> P​teropodidae. — Oh boy
<discord-_> P​teropodidae. — I am sorely underprepared for the math in that paper
<discord-_> M​yshiko. — beautiful and mysterious!
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<_whitenotifier-d13c> [Principia] pleroy reviewed pull request #2549 commit - https://git.io/JfGME
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