egg|nomz|egg 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.
* UmbralRaptor
hopes that this implementation is accurate.
<egg|anbo|egg>
whitequark: is the kneading thing also a central pattern generator?
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<UmbralRaptor>
egg: floating point cats?
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<egg|anbo|egg>
UmbralRaptor: so the ANBOscope is too light for the mount (it's balanced with no counterweights if I put n eyepiece, otherwise scope-light)
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<egg|anbo|egg>
UmbralRaptor: also the mount came with an adapter for car cigar lighter thingy, but fortunately I found an old 12 V DC coax centre-positive supply in a drawer somewhere
<egg|anbo|egg>
UmbralRaptor: losmandy GM8 (not with the goto thing, just clock drive)
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<egg|anbo|egg>
(yes that's overkill to hold the ANBOscope)
<UmbralRaptor>
hah
<egg|anbo|egg>
UmbralRaptor: maybe I'll get a larger ANBOscope eventually but for now I have this old 60 mm f/13.3 refractor with Naglers and a GM8 :-p
<UmbralRaptor>
pics?
<whitequark>
egg|anbo|egg: probably
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<egg|anbo|egg>
!wpn whitequark
* Qboid
gives whitequark a completely harmless semimetal with a spear attachment
<egg|anbo|egg>
!wpn UmbralRaptor
* Qboid
gives UmbralRaptor an octanitrocubane 2N3906
<egg|anbo|egg>
!wpn Fiora
* Qboid
gives Fiora a copper tombstone with a ham radio attachment
<kmath>
<ProbFact> Notation for saying random variables X and Y are independent. The symbol between X and Y is U+2AEB in Unicode. Don'… https://t.co/jyJFAeaTN0
<UmbralRaptor>
sort of
<egg|anbo|egg>
"atmospheric refraction causes objects near the horizon to move at slightly different rates, a fact discovered by an astronomer by the name of King"
<egg|anbo|egg>
which is why there is a tracking rate with a crown on the losmandy control panel >_>
<UmbralRaptor>
Hah
<egg|anbo|egg>
UmbralRaptor: not sure how the mount knows the altitude which it would need for refraction compensation, since the latitude setting is manual
<UmbralRaptor>
egg|anbo|egg: some guess based off of sec(distance from zenith)?
<egg|anbo|egg>
UmbralRaptor: how do you know where the zenith is though
<egg|anbo|egg>
UmbralRaptor: with the weather I can probably use this mount mostly to measure the proper motion of cows
<egg|anbo|egg>
UmbralRaptor: actually the cows might be inside
<egg|anbo|egg>
so the proper motion of barns?
<UmbralRaptor>
Those should be approximate zero.
<UmbralRaptor>
So should their peculiar velocity.
<UmbralRaptor>
Uh, I'm somewhat confused by the scope now. Does it just know its lattitude, dec, and ra(sort of)?
<egg|anbo|egg>
UmbralRaptor: I don't know what it knows
<egg|anbo|egg>
maybe there's a sensor in the latitude dial?
<egg|anbo|egg>
it has RA/dec steppers
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<UmbralRaptor>
Happy darkest day of the year! (some restrictions apply)
<UmbralRaptor>
In a painfully on point note, the 2016 mortality data is out. (US life expectancy decreased by 0.1 years)
<SnoopJeDi>
apparently first time since the 60s for a back-to-back decrease?
<SnoopJeDi>
(where did these stats come from, the NFL?)
<UmbralRaptor>
CDC
<SnoopJeDi>
oh no I meant the meta-stat about the 60s thing
<SnoopJeDi>
I'm mocking my own stat, not actually asking :P
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<APlayer>
OK, so assuming a flat-earth simplification, given a state vector, how would you describe a ballistic trajectory parabola? Any links on this?
<APlayer>
Flat earth and uniform gravity, that is
<SnoopJeDi>
huh?
<SnoopJeDi>
oh you mean "how do you get uniform gravity with Flat Earth?"
<APlayer>
Nope
* UmbralRaptor
is confused at the question.
<SnoopJeDi>
yea you describe a parabola as...a parabola
<APlayer>
If you take the earth, for mathematical simplicity assume it to be flat and have uniform gravity and now you have a rocket with a state vector
<SnoopJeDi>
the flatness isn't particularly relevant
<APlayer>
Is there a way to convert the state vector to a parabola (in 2D, even) that describes altitude vs. downrange?
<SnoopJeDi>
(unless you really wanna write stuff down in the rotating frame)
<APlayer>
I need to account for the rotation too, yes
<SnoopJeDi>
I'm getting more confused by what you're asking, not less :P
<APlayer>
It's about pinpoint landings, or rather, boostback burns that target a specific impact location
<APlayer>
OK, so you have a rocket on a ballistic trajectory
<APlayer>
You need to get it to impact at a specific location
<APlayer>
Assume the earth is flat and the gravity is uniform
<UmbralRaptor>
Okay, so we want x, y, z(t) given an initial trajectory in a rotating reference frame and uniform gravity?
<UmbralRaptor>
(rotating so we get centrifugal, coriolis, etc forces)
<APlayer>
Nah, ignore all those details
<APlayer>
Assume it is 2D, so I can simply account for the rotation using a fixed velocity offset, I guess
<SnoopJeDi>
the bit about there being a rotating sphere requires that you move to an inertial frame (probably centered at the CoM of the planet!) and express both the rotation and the (still constant-acceleration!) ballistic trajectory
<APlayer>
At that scale and the accuracy I need, let's just assume "the ground moves"
<SnoopJeDi>
probably not a very good assumption unless you're launching equatorially
<APlayer>
I am
<APlayer>
I plan to support inclined launches, but I'll expand the maths at a later point
<APlayer>
Start small first
<egg|phone|egg>
!Wpn UmbralRaptor
* Qboid
gives UmbralRaptor a shining partisan
* egg|phone|egg
pets ANBOcat
<SnoopJeDi>
well, at some point, adding a bunch of hodge-podge is larger/more work than doing it The Right Way :P
<APlayer>
A shining partisan?
<APlayer>
SnoopJeDi: I am hoping I can just assume a constant movement of the ground
<SnoopJeDi>
but anyway yea, be careful about your choice of reference frame (as explicit as you can about what coordinates *mean*) and crank away on basic kinematics
<APlayer>
For number reference, I am launching in KScale64 and reaching peak apogee of about 105 km, with horizontal velocities of around 500 m/s
<APlayer>
On that scale, I basically stay atop the KSC as far as the surface motion is concerned
<egg|phone|egg>
C∞ cat
<APlayer>
egg: How many cats do you have?
<APlayer>
Or do you only know how fast they are moving? :P
<APlayer>
(I know this is not how it works, but it was a reference)
<Ellied>
huh, I suppose angular momentum would just be a scalar in 2D space
<Ellied>
since the only possible rotational axis is orthogonal to the universe
<SnoopJeDi>
you could still talk about the direction, it's just not an on-the-manifold sort of property
<SnoopJeDi>
(this is probably a thing someone has done with a 1+1 or 2+1 spacetime?)
<SnoopJeDi>
wait no 1+1 doesn't make sense nvm, but 2+1 yea probably?
<SnoopJeDi>
c.f. AdS/CFT correspondence and black hole angular momentum?
* APlayer
is starts fearing a topic only rarely just because someone mentions a word. But "manifold" is one of the words that induce uncontrollable panic for him
* Ellied
pokes APlayer with Manifold Garden
<SnoopJeDi>
!wpn -add:wpn manifold
<Qboid>
SnoopJeDi: Weapon already added!
<APlayer>
I really need to face it one day and figure out what manifolds are all about
<APlayer>
I guess I'll need it in Uni
<SnoopJeDi>
weirdly, I'm pretty comfortable with it in the math sense, but if I hear it in the engine-y sense my brain just breaks
<SnoopJeDi>
APlayer, if you can understand that Earth is a 2-dimensional surface "embedded" in a 3D space, you've got plenty to work with
<APlayer>
Embedded?
<APlayer>
Located?
<SnoopJeDi>
embedded is a rigorous term here
<SnoopJeDi>
the details of that aren't terribly important
<SnoopJeDi>
the important thing is that there's a surface
<APlayer>
As an analogy, is a sheet of paper embedded in my room?
<APlayer>
Or is that something about the properties of the 3D space itself?
<SnoopJeDi>
much more the latter
<SnoopJeDi>
it does not "just" mean "contained in"
<SnoopJeDi>
closely related to the subject Ellied sidled up to: "if the universe is all this, what's outside that?"
<APlayer>
Wikipedia disagrees: "In mathematics, an embedding (or imbedding[1]) is one instance of some mathematical structure contained within another instance"
<SnoopJeDi>
you'll notice the...rest of the article
<APlayer>
SnoopJeDi: Actually pondered about that three or four times before now
<APlayer>
Did not get to a conclusion yet
<APlayer>
Also, the rest of the article pretty much sums up why "manifold" induces panic for me
<SnoopJeDi>
math wikipedia is garbage
<APlayer>
Comment that in the discussion thread :P
<SnoopJeDi>
I will either be preaching to the choir, or preaching to the mathematicians responsible for such
<SnoopJeDi>
neither is terribly fruitful :P
<APlayer>
...I'm sorry, but the maths in that article is beyond my comprehension
<APlayer>
I'll just accept that as a thing and move it down in my to-learn list to some time when I an more capable to soak it in
<SnoopJeDi>
so the Earth is a 2D surface
<SnoopJeDi>
but we talk about it living in a 3D space (which is really itself a surface!)
<APlayer>
Uh what
<SnoopJeDi>
surface is kind of a bad word I guess, they're all just spaces.
<SnoopJeDi>
APlayer, I'm talking about a spherical Earth, obviously mountains are a thing :P
<SnoopJeDi>
but even on a mountain if you look around on a small enough stepsize, things look flat.
<APlayer>
But what do you mean by "we talk about it living in a 3D space"?
<SnoopJeDi>
okay so
<SnoopJeDi>
put an ant on a cylinder
<SnoopJeDi>
how many unique directions can the ant walk? (remember: a cylinder can be unwrapped into a flat piece of paper)
<APlayer>
...in any direction?
<SnoopJeDi>
just 2, because it's a 2-dimensional manifold, right? (circle-wise and up-and-down the cylinder; left-right on the paper, up-down on the paper)
<SnoopJeDi>
should have said perpendicular directions heh
<APlayer>
Alright, two perpendicular directions
<SnoopJeDi>
anyway, if we think about the cylinder when it's wrapped up though, it's still a 2-dimensional object
<SnoopJeDi>
to the ant's perspective
<APlayer>
If the cylinder is sufficiently large the ant has the same trouble as Flat Earthers have, yep :D
<SnoopJeDi>
to an external observer, we can see that 2-dimension thing is "embedded" in a 3-dimensional space, there's an inside-outside direction
<SnoopJeDi>
it doesn't really have to be particularly large
<SnoopJeDi>
the analogy is kinda problematic because we're trying to use an organism, and organisms are adapted to perceiving 3 dimensions of space haha
<APlayer>
Is it important that it has an inside and an outside?
<SnoopJeDi>
incredibly important!
<SnoopJeDi>
and the ant has *no idea* that the question can even be asked, let alone answered
<APlayer>
What if you have a crumpled napkin?
<SnoopJeDi>
still flat. put a flea on one of the crumples
<APlayer>
Yeah, but no inside
<APlayer>
Only outsides
<SnoopJeDi>
err
<SnoopJeDi>
the inside/outside doesn't really make sense until you're embedded in another space
<SnoopJeDi>
Flatland doesn't have the directions of "in-out", it literally doesn't make sense to talk about that orientation
<APlayer>
But you are? The napkin is, in fact, crumpled?
<SnoopJeDi>
ONLY if you look from the higher space
<SnoopJeDi>
the flea doesn't know it's crumpled
<APlayer>
Alright, but from the perspective of the 3D space, it is
<SnoopJeDi>
yes that perspective is literally the whole point
<APlayer>
And so it is embedded there
<APlayer>
And still has no inside?
<SnoopJeDi>
sure, but it's orientable
<APlayer>
I don't think I understand...
<SnoopJeDi>
orientability is a related but also very separate concept
<APlayer>
Well, let's put aside the fact that things are orientable or have inside/outside surfaces
<SnoopJeDi>
"A surface S is n-embeddable if it can be placed in R^n-space without self-intersections, but cannot be similarly placed in any R^k for k<n"
<APlayer>
I've seen klein bottles before, I guess I understand
<SnoopJeDi>
you've seen what are called immersions of Klein bottles
<SnoopJeDi>
attempts to shove them into 3-space
<SnoopJeDi>
that is *not* the surface, it's literally not possible in 3-space
<APlayer>
(Numberphile for the win :P)
<SnoopJeDi>
(not without self-intersection anyway)
<APlayer>
SnoopJeDi: With some effort, I guess I can wrap my mind around what a klein bottle should be in 4D
<APlayer>
Not true for tesseracts yet, though. (If you know a visualization, that would be amazing :D)
<SnoopJeDi>
you can visualize a projection of one, sure
<APlayer>
Well, no, I mean how to get a hang of what is connected where
<APlayer>
The cubes that are... connected, I guess - really freak me out there
<APlayer>
Anyway, I've got to go now... Thanks a lot for taking your time to shove things into my tight brain, and sorry for sometimes refusing to accept them ;-)
<APlayer>
See you (later, if you'll still be around)!
<SnoopJeDi>
\o
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<egg|anbo|egg>
!wpn UmbralRaptor
* Qboid
gives UmbralRaptor a contingent ear
* UmbralRaptor
should probably do something symbolic about today being the darkest* day of the year.
* UmbralRaptor
grabs a few kg of Pu-239.
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<egg|anbo|egg>
UmbralRaptor: observe?
* egg|anbo|egg
can't do that what with fog
<soundnfury>
!wpn egg|anbo|egg
* Qboid
gives egg|anbo|egg a ?/field hybrid
<UmbralRaptor>
egg|anbo|egg: maybe. currently somewhat working on AAS 231 poster.
<awang>
!u ?
<Qboid>
U+1332A EGYPTIAN HIEROGLYPH T030 (?)
<awang>
Hmmm
<awang>
Looks like my terminal has some work to do with wide-character support
<kmath>
<mcclure111> Please note: Per ISO ISO 8601 if it is not formatted like 1994-11-05T08:15:30-05:00 it is not a date, it is just "hanging out"
<egg|anbo|egg>
!wpn Ellied
* Qboid
gives Ellied a fountain pen which vaguely resembles a square
<UmbralRaptor>
!wpn egg|anbo|egg
* Qboid
gives egg|anbo|egg a tantalum kindle
<UmbralRaptor>
egg: ANBOscope looks far less silly than eggspected.
<egg|anbo|egg>
what were you eggspecting
<UmbralRaptor>
The telescope to look comically undersized.
<egg|anbo|egg>
UmbralRaptor: well there's also perspective
<egg|anbo|egg>
but it is a fairly long 60 mm (800 mm focal) so it's not *tiny*
<soundnfury>
These telescopes are _small_. _These_ telescopes are _far away_.
<UmbralRaptor>
As long as the telescope isn't hard to see from (1+z)^-4 dimming
<egg|anbo|egg>
UmbralRaptor: amusingly the focuser is pretty much exactly the right diametre for 31,75 mm eyepieces (although it came with a 24,5 mm eyepiece holder originally)
<egg|anbo|egg>
(I mean, sure, the short 80 mm I have in zurich would look way more ridiculous than the ANBOscope on this mount, but still it's obviously overkill)
<egg|anbo|egg>
(the fact that I need to remove the weight to reach balance being an example :-p)
<UmbralRaptor>
well, yes.
<egg|anbo|egg>
UmbralRaptor: also I'd expect barns to have high proper motion, since they tend to be attached to planets,
<UmbralRaptor>
egg|anbo|egg: barns are quite small, unless you're making them out of samarium or something.
<soundnfury>
xD
<egg|anbo|egg>
UmbralRaptor: I may have forgotten to get lighting for the polar alignment scope >_>
<UmbralRaptor>
egg|anbo|egg: for $22k, you could cover both years of stipend for a Master's student at MSU.
<egg|anbo|egg>
UmbralRaptor: or 37 semesters at ETHZ >_>
<UmbralRaptor>
egg|anbo|egg: no, no. Not class costs. I mean that's how much it would coat you to have a grad student to do research for you.
<UmbralRaptor>
s/coat/cost/
<Qboid>
UmbralRaptor meant to say: egg|anbo|egg: no, no. Not class costs. I mean that's how much it would cost you to have a grad student to do research for you.
<egg|anbo|egg>
... right, US, you pay MSc students
<egg|anbo|egg>
(at ethz it's only the Phd programmes that have that)