Physics Forums

Physics Forums (http://www.physicsforums.com/index.php)
-   Astronomy & Astrophysics (http://www.physicsforums.com/forumdisplay.php?f=71)
-   -   Super-galactic plane (http://www.physicsforums.com/showthread.php?t=61166)

Graham Fox Jan25-05 02:59 PM

Super-galactic plane
 
Hello all,
I'm researching in the field of ancient cosmology and the history of associated astrological beliefs. I'm working on the links between the galactic and supergalactic planes and systems of organising and dividing the ecliptic. There are a number of astronomical references for where the galactic equator intersects with the ecliptic (notably Marcel Meuss and the US Navy Observatory, who respectively put the ascending or "north" galactic node at the winter solstice point (270) in May and late October 1998 -specifically the 27th October. Does anyone know if there are comparable estimations for the location on our ecliptic of the supergalactic nodes? I've only found one so far, on a site about astronomy for astrologists, but it's rather old and I'm not sure if it reflects current knowledge (it claims 01616'11" for the ascending Super-GN, but doesn't specify the date, I think it's 1950 judging by the other info given). I think there are more reliable references on the web, but in galactic coordinates, and I don't know how to convert into ecliptic coordinates.
Many thanks for any help or ideas.
Graham

selfAdjoint Jan25-05 03:29 PM

I know nothing about the super-galactic nodes, but I would advise you to use the HO (Naval Observatory) value of the ecliptic nodes and treat Marcel Meuss' value as a deviation from it. Among the ancients who determined the position of these nodes were Hipparchos and (possibly faked) Ptolemy. The Islamic astronomers were much into this calculation, as I believe were the Hindus. I am sorry I can't give you names, but the Dictionary of Scientific Biography (many volumes, check index for ecliptic) is a fine source for this material. containing detailed essays impossible to find elsewhere.

(Added) You know, of course, that the location of the ecliptic nodes varies over time (precession of the equinoxes, discovered by Hipparchos). There is probably software that can give you the value for any earlier epoch. Maybe some of our enthusiasts for this capability will enlighten us.

Graham Fox Jan26-05 05:38 AM

Thanks very much for your help. Yes, I was already treating the US Naval value for galactic nodes as the more reliable. I am of course aware that the galactic (and super-galactic nodes) change in terms of tropical (astronomical) coordinates with precession, but that's what I'm looking into: the different values and markers taken in various cultures for the "fixed" sidereal "zodiac" (notably the various values in use in India and in Indian traditions). In sidereal ("fixed") coordinates, the galactic nodes probably do move very very slowly over enormous periods in time, but it would seem that they are much more stable than the so-called "fixed stars", as they represent in a sense the sum total of the relationship of our ecliptic to our galaxy. Thanks again for your pointers, and please do let me know if you should find anything abut the supposed location of the super-galactic ecliptic nodes.
Many thanks
Graham

Chronos Jan26-05 05:55 AM

Graham, look at the WMAP data and analyses before you waste a bunch of time analyzing galactic tilts relative to this galaxy. If there were a preferred orientation of matter in the observable universe, it would show up there. It doesn't. But it's OK to be stubborn. Vizier has a huge amount of data. Play with the link, search and enjoy:
http://vizier.u-strasbg.fr/viz-bin/Cat?J/ApJ/569/23

Graham Fox Jan26-05 03:57 PM

Thanks for the link, Chronos, finding it a bit difficult to find my way around but maybe I'll learn. If you're saying that there is no such such thing as an organisation of our galaxy (and maybe of the group of galaxies ours is within), I don't understand how the US Naval Observatory think they can locate its plane (galactic equator), or indeed where all those lovely spirally pictures we see come from (or flying-saucer shaped, depnding on the angle). But I'm obviously rather out of my depth...
All the best
Graham

selfAdjoint Jan26-05 05:42 PM

Quote:

Quote by Graham Fox
Thanks for the link, Chronos, finding it a bit difficult to find my way around but maybe I'll learn. If you're saying that there is no such such thing as an organisation of our galaxy (and maybe of the group of galaxies ours is within), I don't understand how the US Naval Observatory think they can locate its plane (galactic equator), or indeed where all those lovely spirally pictures we see come from (or flying-saucer shaped, depnding on the angle). But I'm obviously rather out of my depth...
All the best
Graham

Maybe we're not understanding you? Our galaxy is an organized shape, has a center bulge and a disk of stars and gas expending far around it, and has at least a statistically defined central plane, and it is the nodes of this plane, where it's line of intersection with the plane of earth's orbit intersects that orbit, that I was thinking you meant. Other galaxies have various shapes and most of them could be defined to have a central plane, but those galaxies would not have been visible (except possibly Andromeda) to ancient pre-telescopic peoples. Our own galaxy of course appears in the sky as the milky way and there is a theory ("Hamlet's Mill") that this had a major unrecognized effect on mythology.

If your "super-galactic" term means galaxies outside ours, or maybe even "all" galaxies, then I can't see the application to what you say you are studying.

Graham Fox Jan27-05 04:04 AM

Yes, I was thinking exactly along those lines. I know Hamlet's Mill well, and I've drawn on it a lot. I understand the galactic nodes exactly as you do. As I understand it, our galaxy is part of a group of galaxies which also has an organized shape and a statistically defined central plane which intersects obviously with the galactic plane and also with our ecliptic (the only figure I've been able to find for the latter, which doesn't much interest astronomers, is 016 16 11 in 1950, but this may not be reliable). I believe the system of super-galactic coordinates is known as the Vaucouleur system. Anyway, all I really wanted was confirmation or otherwise, if possible, of this figure of 016 16 11 in 1950. I didn't understand why Chronos said "If there were a preferred orientation of matter in the observable universe, it would show up there. It doesn't.". Otherwise I think we understand each other fine! I guess I'll just have to make do with the one figure I've got.
Thanks - Graham

Graham Fox Jan27-05 03:45 PM

What I'm really asking is: do you think this stuff is valid, and/or are there more recent and reliable data than in the table (see link at end) especially regarding the "super-galaxy"/ecliptic intersections. The references to zodiac signs are here of course in tropical coordinates.

"Cosmic Systems and Their Centers -- A List
1. Solar Sysytem
Center: Sun
2. Local System (Gould's Belt)
This is a group of some 10.8 stars of which the Sun is a member. The Local System, originally thought to be a minute galaxy embedded with the Milky Way, is considered to be an ellipsoid of 700x200 parsecs with the long axis parallel to the New Galactic Longitudes 160 deg/340 and located in Orion-Cygnus spiral arm. The centroid of the Local System is in Virgo at about 15deg25' with nodes to the Ecliptic at 10deg22' of Sagittarius (North node) and Gemini. The system is inclined to the ecliptic by about 66deg. Note -- positions are of the Epoch 1950.0.
3. Local Galaxy ... The Milky Way
Estimated to contain 10 to the 11th stars, The Galaxy is a disc-like structure with a diameter of some 30,000 parsecs, a central elllipsoidal nucleus of about 4000 parsecs, and an average disc thickness of several hundred parsecs. The nodes and center (about 26-degree of Sagittarius) in relation to the ecliptic are given elsewhere. The Sun is located some 10,000 from the Galactic Center.
4. Local Group of Galaxies
The local group includes about a score of member galaxies...the largest of which is the Andromeda Galaxy (M 31), our galaxy, and M-31 revolve around a common center of mass roughly in the direction of 27-degress in the Sign Aries.
5. Local Supergalaxy
Our Galaxy is part of a vast flattened super system of galaxies some 40 megaparsecs in diameter, with the center (at 1 degrees of Libra) in the great Virgo Cluster some 12-16 megaparsecs from our Sun.
Copyright Michael Erlewine" (now deceased)

Plus the table (for 1950), which I can't squeeze in here, especially numbers 21 and 22 (intersection of ascending and descending supergalactic nodes to ecliptic):
http://www.thenewage.com/resources/a...truc.asp?orig=

Many thanks, even just for a quick opinion.
Graham


All times are GMT -5. The time now is 07:47 AM.

Powered by vBulletin Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
© 2014 Physics Forums