Re: Irregulars Question: long term stellar ephemeris
At 10:56 PM 3/29/03 +, Alberto Monteiro wrote: Ronn!Blankenship wrote: Ok, so we can assume that the Sun will keep its current orbit around the Galaxy. But what about other stars? Then you could always do what you do to extrapolate solar system positions: start with the current positions and velocities of all the stars for which you have data, compute the gravitational forces between each pair of stars, then do a stepwise integration. (Of course, you do have access to large blocks of time on a Cray, don't you?) :-) No, but I guess I have some quite weird ideas that I _could_ use if I needed to do that And you'll need to approximate the general gravitational field of the galaxy as a whole. For a description of that, as well as the kind of orbits stars follow in the galactic gravitational field, probably the standard text Ok, I will take a look at them when I am (allegedly) working O:-) [anything that has any semblance to orbital dynamics is fair game in my job] However, I suspect that over the time periods you're talking about (a few x10^6 years), there will be at most only a few close enough encounters between stars to significantly affect the paths of the stars. Stars are really widely separated in our neighborhood of the galaxy. (You are not concerned with the stars in the central regions of a globular cluster or near Sgr A*, which are about the only places they are really crowded . . . ) Unless I am trying to identify Trantor :-) http://www.eso.org/outreach/press-rel/pr-2002/pr-17-02.html http://antwrp.gsfc.nasa.gov/apod/ap021025.html http://antwrp.gsfc.nasa.gov/apod/ap020707.html http://antwrp.gsfc.nasa.gov/apod/ap020521.html http://antwrp.gsfc.nasa.gov/apod/ap011229.html BTW, is Proxima gravitationally bound with Alfa Centauri A and B? Short answer: It seems to have the same space motion, but the orbital period (if it is in orbit) is so long that no one has observed any orbital motion. For the latest information on the system: http://antwrp.gsfc.nasa.gov/apod/ap030323.html http://www.eso.org/outreach/press-rel/pr-2003/pr-05-03.html http://antwrp.gsfc.nasa.gov/apod/ap020715.html http://www.eso.org/outreach/press-rel/pr-2002/pr-22-02.html Some other information on the solar neighborhood: http://antwrp.gsfc.nasa.gov/apod/ap010318.html http://antwrp.gsfc.nasa.gov/apod/ap000411.html http://antwrp.gsfc.nasa.gov/apod/ap000412.html On a tangential note, the Jijo books mention that Izmunuti is 1 light-year away from Jijo-S [whose name is Ganjoo - I guess]. Is it possible that they can keep such a long distance for millions of years? I don't think they can be gravitationally bound that far Maybe. Maybe not. http://www.space.com/scienceastronomy/solarsystem/nemesis_010320-1.html (If you really want to know what the author had in mind, I suppose you could always try asking him . . . ;-) ) -- Ronn! :) Ronn Blankenship Instructor of Astronomy/Planetary Science University of Montevallo Montevallo, AL Disclaimer: Unless specifically stated otherwise, any opinions contained herein are the personal opinions of the author and do not represent the official position of the University of Montevallo. ___ http://www.mccmedia.com/mailman/listinfo/brin-l
Re: Irregulars Question: long term stellar ephemeris
At 01:28 AM 3/29/03 +, Alberto Monteiro wrote: Ronn!Blankenship wrote: I'm not sure about _accelerations_, That's the problem, isn't it? But maybe if we don't expect any two stars to get close enough, Well, let's see: the distance from the Sun to alpha Centauri is about 30,000,000 solar diameters or 60,000,000 solar radii, so what is the attraction between the two stars? An illustration I have heard (not necessarily precise) is that two stars in our Galaxy have about the same chance of colliding as two flies which start from opposite ends of the Grand Canyon. they will just follow some 200 or so million year orbit around the Galaxy, which will reduce to an almost straight line in anything of the order of 10 million years. That is clearly what the author of the ST article (below) did. 10my/225my = 0.28 radians or 16°, a little large for using the small angle formulas (although technically the angle is only +/- 8° from the present position). I suppose one might try approximating the path as an arc of a circle rather than a straight line, though the particular curve fit one used might be as likely to make it less accurate as more accurate than the straight-line approximation. but the Hipparcos/Tycho catalog has the best currently available information on the motions of the stars it lists Ok There was an article in _Sky and Telescope_ within the past few years in which that data was used to determine which star was the apparently brightest star as seen from Earth at any given time during the interval 5 mybp to 5 myap. I believe this is the article: Computers in Astronomy Once and Future Celestial Kings By Jocelyn Tomkin | April 1998, p. 59-63 (PDF: 255 kilobytes) To purchase a copy of the article in PDF format for $2.95US, go to: http://skyandtelescope.com/shopatsky/_additem.asp?aaid=199804059063 Also, here's an item about a red dwarf which will come within 1 ly of the Sun about a million years from now: http://antwrp.gsfc.nasa.gov/apod/ap970626.html m = 1/1000. Do you mean My or ky? mybp is frequently used by geologists as an abbreviation for million years before present. (Frex, Alberio will be the brightest star in the sky about 4.5 my from now.) Does this sound like what you need? Yep - ** if ** they explicitly give an error If so, are you familiar with the Hip/Tyc catalog and its data format, or do you need more information? No; but I guess I can find it quickly with a google search. It's free, isn't it? Probably some Megabytes of data Home page: http://astro.estec.esa.nl/SA-general/Projects/Hipparcos/hipparcos.html I've been using the Gliese3 catalog for some time Unless they've updated it with Hipparcos data, the parallax/proper motion data is out of date. -- Ronn! :) Ronn Blankenship Instructor of Astronomy/Planetary Science University of Montevallo Montevallo, AL Disclaimer: Unless specifically stated otherwise, any opinions contained herein are the personal opinions of the author and do not represent the official position of the University of Montevallo. ___ http://www.mccmedia.com/mailman/listinfo/brin-l
Re: Irregulars Question: long term stellar ephemeris
Ronn!Blankenship wrote: That's the problem, isn't it? But maybe if we don't expect any two stars to get close enough, An illustration I have heard (not necessarily precise) is that two stars in our Galaxy have about the same chance of colliding as two flies which start from opposite ends of the Grand Canyon. But I am not talking about _collision_. I am talking about getting close enough for enough time to change their speeds more than the initial errors in the measurement of those speeds. And there are 100 thousand million flies, or 10 thousand trillion pairs of stars :-) Also, here's an item about a red dwarf which will come within 1 ly of the Sun about a million years from now: http://antwrp.gsfc.nasa.gov/apod/ap970626.html Ok, so we can assume that the Sun will keep its current orbit around the Galaxy. But what about other stars? m = 1/1000. Do you mean My or ky? mybp is frequently used by geologists as an abbreviation for million years before present. Bloody non-standard bastards. What is the abbreviation of year? yr? _Certainly_ m stands for 1/1000, not 10^6 Alberto Monteiro ___ http://www.mccmedia.com/mailman/listinfo/brin-l
RE: Irregulars Question: long term stellar ephemeris
From: Alberto Monteiro [mailto:[EMAIL PROTECTED] Does anyone have any idea of the accelerations [in a non-rotating frame of reference, relative to the Sun] of the stars in the Sun neighbourhood and the bright stars in our sky for some long time? I'm not worried about the _precision_ of the acceleration, as long as I have it for thousands or even millions of years Uh... no... - jmh ___ http://www.mccmedia.com/mailman/listinfo/brin-l
Re: Irregulars Question: long term stellar ephemeris
At 03:57 PM 3/29/03 +, Alberto Monteiro wrote: Ronn!Blankenship wrote: That's the problem, isn't it? But maybe if we don't expect any two stars to get close enough, An illustration I have heard (not necessarily precise) is that two stars in our Galaxy have about the same chance of colliding as two flies which start from opposite ends of the Grand Canyon. But I am not talking about _collision_. I am talking about getting close enough for enough time to change their speeds more than the initial errors in the measurement of those speeds. And there are 100 thousand million flies, or 10 thousand trillion pairs of stars :-) With the average distance between closest pairs comparable to the size of the Grand Canyon. The whole Galaxy at that scale would likely fill a fair amount of the solar system . . . Ok, so we can assume that the Sun will keep its current orbit around the Galaxy. But what about other stars? Then you could always do what you do to extrapolate solar system positions: start with the current positions and velocities of all the stars for which you have data, compute the gravitational forces between each pair of stars, then do a stepwise integration. (Of course, you do have access to large blocks of time on a Cray, don't you?) And you'll need to approximate the general gravitational field of the galaxy as a whole. For a description of that, as well as the kind of orbits stars follow in the galactic gravitational field, probably the standard text is: http://pup.princeton.edu/titles/2537.html and this book goes along with it: http://pup.princeton.edu/titles/6358.html However, I suspect that over the time periods you're talking about (a few x10^6 years), there will be at most only a few close enough encounters between stars to significantly affect the paths of the stars. Stars are really widely separated in our neighborhood of the galaxy. (You are not concerned with the stars in the central regions of a globular cluster or near Sgr A*, which are about the only places they are really crowded . . . ) m = 1/1000. Do you mean My or ky? mybp is frequently used by geologists as an abbreviation for million years before present. Bloody non-standard bastards. What is the abbreviation of year? yr? _Certainly_ m stands for 1/1000, not 10^6 OK, it probably ought to be Mybp. But what can you expect out of geologists? After all, they have rocks in their heads . . . If so, are you familiar with the Hip/Tyc catalog and its data format, or do you need more information? No; but I guess I can find it quickly with a google search. It's free, isn't it? Probably some Megabytes of data Home page: http://astro.estec.esa.nl/SA-general/Projects/Hipparcos/hipparcos.html Actually, the Celestia 2000 program mentioned there fits on a CD-ROM, and I think that must include the data from the catalog, since it runs without needing anything else. That program is mainly for statistical searches, e.g., list all the stars in the HIP/TYC catalog within n parsecs of the Sun (i.e. with parallax greater than 1/n arcseconds) whose annual motion is between lower limit and upper limit, but that's not really what you need. So you'll need to download the catalog and write a program to read it and do the calculations you need. -- Ronn! :) Ronn Blankenship Instructor of Astronomy/Planetary Science University of Montevallo Montevallo, AL Disclaimer: Unless specifically stated otherwise, any opinions contained herein are the personal opinions of the author and do not represent the official position of the University of Montevallo. ___ http://www.mccmedia.com/mailman/listinfo/brin-l
Re: Irregulars Question: long term stellar ephemeris
Ronn!Blankenship wrote: Ok, so we can assume that the Sun will keep its current orbit around the Galaxy. But what about other stars? Then you could always do what you do to extrapolate solar system positions: start with the current positions and velocities of all the stars for which you have data, compute the gravitational forces between each pair of stars, then do a stepwise integration. (Of course, you do have access to large blocks of time on a Cray, don't you?) :-) No, but I guess I have some quite weird ideas that I _could_ use if I needed to do that And you'll need to approximate the general gravitational field of the galaxy as a whole. For a description of that, as well as the kind of orbits stars follow in the galactic gravitational field, probably the standard text Ok, I will take a look at them when I am (allegedly) working O:-) [anything that has any semblance to orbital dynamics is fair game in my job] However, I suspect that over the time periods you're talking about (a few x10^6 years), there will be at most only a few close enough encounters between stars to significantly affect the paths of the stars. Stars are really widely separated in our neighborhood of the galaxy. (You are not concerned with the stars in the central regions of a globular cluster or near Sgr A*, which are about the only places they are really crowded . . . ) Unless I am trying to identify Trantor :-) BTW, is Proxima gravitationally bound with Alfa Centauri A and B? On a tangential note, the Jijo books mention that Izmunuti is 1 light-year away from Jijo-S [whose name is Ganjoo - I guess]. Is it possible that they can keep such a long distance for millions of years? I don't think they can be gravitationally bound that far Actually, the Celestia 2000 program mentioned there fits on a CD-ROM, and I think that must include the data from the catalog, since it runs without needing anything else. That program is mainly for statistical searches, e.g., list all the stars in the HIP/TYC catalog within n parsecs of the Sun (i.e. with parallax greater than 1/n arcseconds) whose annual motion is between lower limit and upper limit, but that's not really what you need. So you'll need to download the catalog and write a program to read it and do the calculations you need. I once trying to find Nexon-Solaria, based on the fact that they should be G-type stars that lie about 2 parsecs apart. I ended up with too many pairs :-( Alberto Monteiro ___ http://www.mccmedia.com/mailman/listinfo/brin-l
Re: Irregulars Question: long term stellar ephemeris
Alberto Monteiro wrote: (snip) and spend a lot of time doing funny things while the real world explodes around me They've got to be done sometime. -- Matt ___ http://www.mccmedia.com/mailman/listinfo/brin-l
Re: Irregulars Question: long term stellar ephemeris
William Taylor wrote: Are you trying to figure out where the sapient dinosaurs ran off to before they aimed that comet at Earth to help cover their tracks? No - this would require precision of hundreds of millions of years. I just want to map the Robot/Empire/Foundation Galaxy, determine the exact date of the awakening of the Elves in Middle-earth, determine the exact hours of the transitions in The Number of the Beast, and spend a lot of time doing funny things while the real world explodes around me Alberto Monteiro ___ http://www.mccmedia.com/mailman/listinfo/brin-l
Re: Irregulars Question: long term stellar ephemeris
Nick Arnett wrote: Does anyone have any idea of the accelerations [in a non-rotating frame of reference, relative to the Sun] of the stars in the Sun neighbourhood and the bright stars in our sky for some long time? I'm not worried about the _precision_ of the acceleration, as long as I have it for thousands or even millions of years Planning a trip? Yes. Or, rather, analysing some trips Can I go? Only if you have good information to share :-P Alberto Monteiro ___ http://www.mccmedia.com/mailman/listinfo/brin-l
Re: Irregulars Question: long term stellar ephemeris
From: Alberto Monteiro [EMAIL PROTECTED] I just want to map the Robot/Empire/Foundation Galaxy, determine the exact date of the awakening of the Elves in Middle-earth, That could be tricky; I just read the Silmarillion, and even if you believe the Elvish propaganda to be entirely accurate I don't recall clear mentioning of enough stars to judge time. Days would also be hard to count before the Sun and Moon were created. Plus the fact that Ilúvatar sorta kinda reshaped the whole universe around Arda after the whole Númenor debacle. But that shouldn't stop you. :) Joshua _ The new MSN 8: smart spam protection and 2 months FREE* http://join.msn.com/?page=features/junkmail ___ http://www.mccmedia.com/mailman/listinfo/brin-l
Re: Irregulars Question: long term stellar ephemeris
At 11:05 PM 3/27/03 +, Alberto Monteiro wrote: Does anyone have any idea of the accelerations [in a non-rotating frame of reference, relative to the Sun] of the stars in the Sun neighbourhood and the bright stars in our sky for some long time? I'm not worried about the _precision_ of the acceleration, as long as I have it for thousands or even millions of years Alberto, I'm not sure about _accelerations_, but the Hipparcos/Tycho catalog has the best currently available information on the motions of the stars it lists (except for the handful of stars which have had very precise measurements made by the HST Fine Guidance Sensors). There was an article in _Sky and Telescope_ within the past few years in which that data was used to determine which star was the apparently brightest star as seen from Earth at any given time during the interval 5 mybp to 5 myap. (Frex, Alberio will be the brightest star in the sky about 4.5 my from now.) Does this sound like what you need? If so, are you familiar with the Hip/Tyc catalog and its data format, or do you need more information? -- Ronn! :) Ronn Blankenship Instructor of Astronomy/Planetary Science University of Montevallo Montevallo, AL Disclaimer: Unless specifically stated otherwise, any opinions contained herein are the personal opinions of the author and do not represent the official position of the University of Montevallo. ___ http://www.mccmedia.com/mailman/listinfo/brin-l
Re: Irregulars Question: long term stellar ephemeris
Joshua Bell wrote: That could be tricky; I just read the Silmarillion, and even if you believe the Elvish propaganda to be entirely accurate I don't recall clear mentioning of enough stars to judge time. Days would also be hard to count before the Sun and Moon were created. It's not tricky, and I am reduced to _refining_ what I already have http://www.geocities.com/albmont/medating.htm Plus the fact that Ilúvatar sorta kinda reshaped the whole universe around Arda after the whole Númenor debacle. But that shouldn't stop you. :) Of course not. The change of the world was philosophical, with no observable effects :-) I will refine the time of the Awakening as long as I have planetary ephemeris with known errors for 6000 - 4000 BC. Alberto Monteiro ___ http://www.mccmedia.com/mailman/listinfo/brin-l
Re: Irregulars Question: long term stellar ephemeris
Ronn!Blankenship wrote: I'm not sure about _accelerations_, That's the problem, isn't it? But maybe if we don't expect any two stars to get close enough, they will just follow some 200 or so million year orbit around the Galaxy, which will reduce to an almost straight line in anything of the order of 10 million years. but the Hipparcos/Tycho catalog has the best currently available information on the motions of the stars it lists Ok There was an article in _Sky and Telescope_ within the past few years in which that data was used to determine which star was the apparently brightest star as seen from Earth at any given time during the interval 5 mybp to 5 myap. m = 1/1000. Do you mean My or ky? (Frex, Alberio will be the brightest star in the sky about 4.5 my from now.) Does this sound like what you need? Yep - ** if ** they explicitly give an error If so, are you familiar with the Hip/Tyc catalog and its data format, or do you need more information? No; but I guess I can find it quickly with a google search. It's free, isn't it? Probably some Megabytes of data I've been using the Gliese3 catalog for some time Alberto Monteiro ___ http://www.mccmedia.com/mailman/listinfo/brin-l
RE: Irregulars Question: long term stellar ephemeris
-Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Alberto Monteiro Sent: Thursday, March 27, 2003 3:06 PM To: Killer Bs Discussion Subject: Irregulars Question: long term stellar ephemeris Does anyone have any idea of the accelerations [in a non-rotating frame of reference, relative to the Sun] of the stars in the Sun neighbourhood and the bright stars in our sky for some long time? I'm not worried about the _precision_ of the acceleration, as long as I have it for thousands or even millions of years Planning a trip? Can I go? Nick ___ http://www.mccmedia.com/mailman/listinfo/brin-l
Re: Irregulars Question: long term stellar ephemeris
In a message dated 3/27/2003 5:40:02 PM US Mountain Standard Time, [EMAIL PROTECTED] writes: Does anyone have any idea of the accelerations [in a non-rotating frame of reference, relative to the Sun] of the stars in the Sun neighbourhood and the bright stars in our sky for some long time? I'm not worried about the _precision_ of the acceleration, as long as I have it for thousands or even millions of years Alberto Monteiro PS: yes, I will use them in timelines Are you trying to figure out where the sapient dinosaurs ran off to before they aimed that comet at Earth to help cover their tracks? ...just an irregular thought. ;-) William Taylor - Contacting Aliens gave away too many clues. ___ http://www.mccmedia.com/mailman/listinfo/brin-l
