raptop changed the topic of #kspacademia to: https://gist.github.com/pdn4kd/164b9b85435d87afbec0c3a7e69d3e6d | Dogs are cats. Spiders are cat interferometers. | Космизм сегодня! | Document well, for tomorrow you may get mauled by a ネコバス. | <UmbralRaptor> egg|nomz|egg: generally if your eyes are dewing over, that's not the weather. | <ferram4> I shall beat my problems to death with an engineer. | We can haz pdf
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<egg|cell|egg>
I'm vaguely hungry
<egg|cell|egg>
It is 2 in the morning
<egg|cell|egg>
Hmm
<UmbralRaptor>
2 am waffles
<SilverFox>
belgian waffles are best waffles
<SilverFox>
fight me
<UmbralRaptor>
eigenwaffles are the correct waffles, however
<B787_300>
UmbralRaptor: what about Eulerwaffles?
<B787_300>
i mean the dude has his name on almost everything
<egg|z|egg>
UmbralRaptor: sufficiently circular orbits have 4 apsides
<UmbralRaptor>
hrm
<egg|z|egg>
this is something you quickly notice when poking at principia
<egg|z|egg>
UmbralRaptor: this is also something i'm going to need to deal with in the orbit analyser
<egg|z|egg>
right now, on 3.5 days of the orbit of TOPEX/Poséidon, it finds 90 periapsides, 90 apoapsides, 45 ascending nodes
<egg|z|egg>
it then calculates an anomalistic period of T = +3372.71(16) s and a nodal period of T☊ = +6745.803(35) s, which is obviously nonsense
<mofh>
egg|z|egg: wait, there are *multiple definitions* of what the days correspond to in the calendrier républicain?
<mofh>
07:21:53 <@egg|z|egg> ""One would expect more mathematical simplicity, rather than more complexity, for nearly circular orbits,"
<mofh>
I MEAN YES, I VERY MUCH WOULD. Is that seriously not the case? Nearly circular orbits are *nastier* mathematically than those that are not?
<egg|z|egg>
mofh: the only definition that was ever law was that the equinox is on the 1er vendémiaire
<egg|z|egg>
mofh: that means, like leap seconds, that it's an astronomical determination, so extrapolations can be tricky (less so than the rotation of the earth but still); in particular at the time they were concerned about year CXLIV whose equinox would fall within 20 s of midnight
<egg|z|egg>
mofh: Romme proposed a Gregorian-style fixed rule, but was shortened before that silliness ever made it into law
<galois>
title: French Republican calendar - Wikipedia
<galois>
[WIKIPEDIA] French Republican calendar#Converting from the Gregorian Calendar | "The French Republican calendar (French: calendrier républicain français), also commonly called the French Revolutionary calendar (calendrier révolutionnaire français), was a calendar created and implemented during the French Revolution, and used by the French government for about 12 years from late 1793..."
<egg|z|egg>
mofh: the IMCCE calendar provides calendar correspondences, and I believe they use the astronomical definition as well (they *are* the IMCCE)
<mofh>
egg|z|egg: i mean the only sensible things to do are Gregorian-style fixed rules or literally propagate the calendar analeptically wrt the equinoxes
<mofh>
which as you just mentioned will lead to deviations and error in the future
<egg|z|egg>
analeptically?
<mofh>
so i'm not entirely sure why you claim that Romme's method is silliness :p
<egg|z|egg>
well, because if you want it to be aligned with the tropical year, the only solution is to make it definitional
<egg|z|egg>
otherwise you're going to end up noticing that it doesn't quite match up with your rational number of choice
<mofh>
okay, fair. but then you're computing a lunisolar calendar in t--okay i guess if the Chinese can do it for so long i don't have an excuse
<egg|z|egg>
mofh: nah, it's purely solar, the moon isn't involved in that one
<egg|z|egg>
you're just computing ephemerides
<egg|z|egg>
mofh: e.g. Herschel found that you needed to make multiples of 4000 leapy to better approximate the tropical year
<galois>
[WIKIPEDIA] Gregorian calendar#Accuracy | "The Gregorian calendar is the calendar used in most of the world. It is named after Pope Gregory XIII, who introduced it in October 1582. The calendar spaces leap years to make the average year 365.2425 days long, approximating the 365.2422-day tropical year that is determined by the Earth's revolution..."
<galois>
title: Gregorian calendar - Wikipedia
<mofh>
Huh, that's a neat result.
<egg|z|egg>
mofh: what do you mean by analeptically
<egg|z|egg>
> (medicine) A kind of epileptic attack, originating from gastric disorder.
<egg|z|egg>
<< not sure this is a good way to determine your calendar
<UmbralRaptor>
aaaaaa
* egg|z|egg
pets UmbralRaptor
<mofh>
egg|z|egg: i thought that's the correct word for proleptic, but forwards in time instead of backwards
<egg|z|egg>
that's possibly right
<mofh>
like the proleptic gregorian calendar is you take the gregorian rule and you propagate it backwards
<mofh>
this is taking the equinox rule and propagating it forwards
<egg|z|egg>
mofh: but isn't "literally propagate the calendar analeptically wrt the equinoxes" just the definition that was used?
<egg|z|egg>
i.e. the astronomical one?
<egg|z|egg>
mofh: anyway, this means converting between the two calendars can be done in several ways, and absolutely cannot be done independently of the year
<mofh>
yeah i didn't realize the rule was JUST "the autumnal equinox is 1 Vendémiaire"
<egg|z|egg>
yup
<egg|z|egg>
mofh: probably with some sort of "as measured at the observatoire" somewhere :-p
<mofh>
since wouldn't that alone occasionally give you 5 years between leap years in the calendar?
<egg|z|egg>
mofh: it would, obviously
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<mofh>
and i assumed there was another rule to fix that up
<mofh>
(but it turns out there just isn't???)
<egg|z|egg>
it didn't before Napoléon got rid of it, but it would have
<egg|z|egg>
mofh: so the equinox definition has a leap before CCXXVII and Romme before CCXXIX instead
<egg|z|egg>
which means the two systems are currently disagreeing by one day
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<mofh>
yeah i mean i figure they'd disagree, impressed the delta is only a day.
<egg|z|egg>
mofh: the wikipedia "current date" thing uses romme because they are counter-revolutionary cowards who can't be arsed to write an ephemeris in their calendar widget :-p
<egg|z|egg>
mofh: yeah if you look at the table they give, there was a leap day before year XII, the equinox definition would have given a leap year before year XVI, but not before year XX
<egg|z|egg>
mofh: at the time they were able to predict things up to CXLIV so it would definitely have been usable as a definition
<mofh>
ahh.
<egg|z|egg>
and I think by the 1930s you have the requisite accuracy to resolve that equinox (especially since there is much less extrapolation going on)
<egg|z|egg>
• L’an 227 du calendrier républicain (1er vendémiaire) débute le 23 septembre 2018 et se termine le 22 septembre 2019.
<egg|z|egg>
with the note: Le premier jour de l’année républicaine tombe le jour de l’équinoxe d’automne calculé pour le méridien de Paris (en temps moyen de Paris)
<mofh>
ahh.
<mofh>
i wonder if the difference between Paris and Greenwich is meaningful enough to ever matter in the future when calculating dates
<mofh>
(and if yes, how far you need to go before you get a day's delta)
<egg|cell|egg>
Mofh: just need an equinox very close to midnight
<egg|cell|egg>
Mofh: the year CXLIV one 20 s from midnight is definitely close enough
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* UmbralRaptop
stares at insurance website in confusion
<egg|z|egg>
UmbralRaptop: mofh: blarg I don't know how to handle circular orbits
<egg|z|egg>
<mofh> I MEAN YES, I VERY MUCH WOULD. Is that seriously not the case? Nearly circular orbits are *nastier* mathematically than those that are not? <<< hahaha
<egg|z|egg>
hahahahahahahahahahhahaha
<egg|z|egg>
mofh: they have four apsides
<egg|z|egg>
per orbit
<egg|z|egg>
two periapsides at the poles, two apoapsides at the equator
<egg|z|egg>
with no precession of those apsides
<egg|z|egg>
(mind you, there is some sort of underlying e and ω and that ω may precess, but it doesn't correspond to eggstrema of distance so it's a right mess
<galois>
title: Robin Leroy on Twitter: "Ryan P. Russel and Martín Lara (2006), Repeat Ground Track Lunar Orbits in the Full-Potential Plus Third-Body Problem. AIAA/AAS Astrodynamics Specialist Conference and Exhibit, 21 – 24 August 2006; ASC-25: Orbital Dynamics, Perturbations, and Stability. AIAA 2006-6750.… https://t.co/9lt46X9ssR"
<egg|z|egg>
(but it has eccentricity vector cycle plots)
<Iskierka>
a miaou!
<Iskierka>
I have no idea what those graphs are
<egg|z|egg>
Iskierka: the oddly shaped graphs at the bottom of page 13 are graphs of the eccentricity vector over a cycle of the ground track
<egg|z|egg>
left is osculating at all times, right is only at the nodes so short-period oscillations are hidden
<egg|z|egg>
the eccentricity vector being (e cos ω, e sin ω), ω being the argument of periapsis
<_whitenotifier-5dfc>
[Principia] pleroy opened pull request #2183: Fix problems found on Linux - https://git.io/fjRAc
<_whitenotifier-5dfc>
[Principia] eggrobin labeled pull request #2183: Fix problems found on Linux - https://git.io/fjRAc
<mofh>
egg|z|egg: wait, with *NO* precession of apsides? how does that work???
<egg|z|egg>
mofh: because they're not real apsides
<egg|z|egg>
mofh: they're extrema of distance, sure
<egg|z|egg>
but they're induced by oblateness
<egg|z|egg>
the real apsides are hidden by oblateness at very smol eggscentricities
<egg|z|egg>
(they keep precessing, but they don't yield eggstrema of distance so they're not very tangible)
<egg|z|egg>
by "real" I mean keplerian in some sense (or really the apsides tied to the perturbation theory that you're using to talk about mean elements)
<egg|z|egg>
but this all sounds like I really need a mean element theory to do anything useful
<egg|z|egg>
at the very least a J2-aware mean element theory
<egg|z|egg>
can't just look at discrete apsides, because those will get garbaged
<egg|z|egg>
mofh: see figure 1 of that smol eggscentricities paper
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<egg|zzz|egg>
!wpn UmbralRaptor
* galois
gives UmbralRaptor a harmless asymptote
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<B787_300>
Well I have no power or internet... and there is more weather expected later this week
<UmbralRaptor>
!wpn egg|z|egg
* galois
gives egg|z|egg a barium vulture with a shell attachment
<UmbralRaptor>
!wpn B787_300
* galois
gives B787_300 a nitrogen cannon
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<egg|z|egg>
!wpn UmbralRaptop
* galois
gives UmbralRaptop a cow with a explosive attachment
<UmbralRaptop>
(The attachment is a lactase inhibitor)