These are chat archives for astropy/astropy

1st
Aug 2017
matrixbot
@matrixbot
Aug 01 2017 16:21
TreyHarris on Freenode Hi--I'm hoping an expert can help out a dumb layman who just needs something for a game I'm working on. This is one of those practical "if you've done it, it's easy, if not, it's hard" things I think: anyone know how to use catalogue data to determine how far away from us a star will be X years in the future? I've read astro textbooks, and I know the method of converting RA/dec/parallax to Cartesian, then
TreyHarris on Freenode converting R-v and proper motion int Cartesion vectors, then applying them and reversing the whole thing to get a new RA/dec/parallax. But seeing how many astro-related libs there are, I bet there's a python module for this? I actually just need distance at year M in the future, where M < 2000. I can do this purely numerically using the method above, but it's cumbersome (particularly since several values in
TreyHarris on Freenode published catalogues are the wrong units or referenc poitns for this calculation so need conversion before I can even do the simple Cartesian vector work).
TreyHarris on Freenode I skimmed the astropy tutorial and examples, and it looks like it can probably help me, but I don't know real astronomy well enough to figure out how.
matrixbot
@matrixbot
Aug 01 2017 16:29
TreyHarris on Freenode (Also, throw in error values and especially error ellipses, and I'm truly lost. I don't even know whether, because I'm talking about objects close to us--specifically, ones less than M ly away for ever M years in the future, with M < 2000, that means the errors aren't that important because the time period is short and the errors are small, or whether I do need to pay attention to margins of error precisely
TreyHarris on Freenode because they're so close the possible sky movement is greater....)
matrixbot
@matrixbot
Aug 01 2017 16:55
TreyHarris on Freenode Urgh, working this brute-force, I can see that this is hard because stars may get closer to us for some period of the next 2000 years, then move farther away, so unlike a simple margin of error where I could work out an overall margin of error for the distance-to-us scalar, these error ellipses mean I end up with a complex answer with an error ellipsoid, don't I? The idea in the game--and I can precompute as
TreyHarris on Freenode much as necssary and store it--is, assuming a signal goes out from here at a given time, whether a given star "has seen it" by some later time or not.
TreyHarris on Freenode So I guess I need a two-dimensional array of answers to the question, "the minimum possible distance of the star to us between now and time M in M between now and ~4017 CE", where the number of subdivisions is arbitrary, lesser or greater depending on how much accuracy I want (if years, 2000 of them, for instance), and if given array-lookup function d, d(M) < M × c for any M <= Y, where Y is the future year
TreyHarris on Freenode I'm asking about, then the signal could have reached it. (The optimization of making the second column of the array strictly increase--i.e., once the star has reached periapsis to our Sun, stop calculating--would be valid if all signals in the game left at M=0, but that's not the case, so I can't make that optimization.) Since it's just a game, I could just ignore the errors entirely and pretend some
TreyHarris on Freenode catalog's values are exactly correct, I guess...
TreyHarris on Freenode (And I'm sure "periapsis" isn't the correct term when talking about the sun and a faraway star--I meant "closest approach", whatever the term is.)
matrixbot
@matrixbot
Aug 01 2017 17:06
TreyHarris on Freenode Hmm... is the silence an indication that this is the wrong channel for this? If so, can someone direct me somewhere more appropriate? ##astronomy seems too general... I also tried #pyastro before seeing it was a channel created for a conference that's already happened...
matrixbot
@matrixbot
Aug 01 2017 17:20
equant on Freenode Sometimes replies take a long time in here, but considering the length of your question, it seems like there has to be a Stack Exchange that would be good for you.
TreyHarris on Freenode equant: I kept adding stuff as I was hacking away at the brute-force solution and thought maybe the additional context might help. But yes, I'll got to stack exchange if IRC can't help me.
matrixbot
@matrixbot
Aug 01 2017 17:29
TreyHarris on Freenode equant: would the astronomy.stackexchange.com be the better place for this than a programming-related one, do you think?
matrixbot
@matrixbot
Aug 01 2017 18:22
TreyHarris on Freenode I'll give it a try. Thanks.