Spiral galaxies

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malcm
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Spiral galaxies

Post by malcm » Wed Oct 22, 2008 7:14 pm

Do spiral galaxies revolve (apparently) in a clockwise direction, as does a 4th of July pinwheel or, COUNTER clockwise, as I've read somewhere, which wd seem unlikely - unwinding as it goes?

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bystander
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Re: Spiral galaxies

Post by bystander » Wed Oct 22, 2008 7:52 pm

malcm wrote:Do spiral galaxies revolve (apparently) in a clockwise direction, as does a 4th of July pinwheel or, COUNTER clockwise, as I've read somewhere, which wd seem unlikely - unwinding as it goes?
There are examples of both.

http://apod.nasa.gov/cgi-bin/apod/apod_ ... ral+galaxy

I think I even remember one example that had outer arms rotating one way with counter rotating inner arms.

http://apod.nasa.gov/apod/ap070802.html

Here the foreground is clockwise, the background counter

http://apod.nasa.gov/apod/ap080420.html

Here's one that defies conventional wisdom.

http://apod.nasa.gov/apod/ap040221.html

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Chris Peterson
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Re: Spiral galaxies

Post by Chris Peterson » Wed Oct 22, 2008 9:30 pm

malcm wrote:Do spiral galaxies revolve (apparently) in a clockwise direction, as does a 4th of July pinwheel or, COUNTER clockwise, as I've read somewhere, which wd seem unlikely - unwinding as it goes?
Normal spiral galaxies revolve like pinwheels (cw and ccw don't apply, as we see galaxies from both sides). This is true for the vast majority of spiral galaxies.

The situation is complicated by galaxies which are the product of collisions or mergers, which can be left rotating either with or against their arms, or even rotating in different directions at different radii.
Chris

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malcm
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Your list!

Post by malcm » Wed Oct 22, 2008 10:00 pm

:D Bystander: Your reply, including a list of 200 APOD galaxy items, is PRICELESS! How did you do that?! Many thanks! I hope I can save it & browse thru it frequently. I noticed that ARP271 is included. Particularly interesting to me, for Halton (Chip) Arp was a fencing buddy of mine many years ago as we competed on maestro Ralph Faulkner's team. We had a nice visit a few years ago as I passed thru Munich. He continued in fencing competition successfully in Europe when he joined the astronomy staff at the Max Planck Institute. I have two of his books. Thanks, again, for your prompt & extensive answer to my query. malcm.

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Post by malcm » Wed Oct 22, 2008 10:09 pm

Thank you, too, Chris - I've added Cloudbait to my favorites list.

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BMAONE23
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Post by BMAONE23 » Wed Oct 22, 2008 11:42 pm


malcm
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BMAONE23 - Thanks

Post by malcm » Thu Oct 23, 2008 3:39 am

Great websites! I already have 21"X27" mounted blowups around the house & am running out of wall space. Have to start using the doors, I guess. The pix we're getting in this past decade are just mind=blowing!

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Post by harry » Thu Oct 23, 2008 6:09 am

G'day from the land of ozzzz

Bmaone23 my kid thanks you for the link

Great easy selection of galaxies

Ta
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Post by bystander » Thu Oct 23, 2008 12:43 pm

malcm wrote:Bystander: Your reply, including a list of 200 APOD galaxy items, is PRICELESS! How did you do that?!
The Search feature is found at the bottom of every APOD!

BTW: Welcome to Asterisk, malcm!

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BMAONE23
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Post by BMAONE23 » Thu Oct 23, 2008 1:50 pm

harry wrote:G'day from the land of ozzzz

Bmaone23 my kid thanks you for the link

Great easy selection of galaxies

Ta
Thanks,
It has ben in my favorites for many months now.

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Galaxy''s

Post by alexandrie » Thu Nov 06, 2008 7:10 pm

Do all galaxy"turn the same direction studying the photograph"s thy all seem to turn from right to left :?:

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Re: Galaxy''s

Post by jesusfreak16 » Thu Nov 06, 2008 7:39 pm

left to right: http://apod.nasa.gov/apod/ap030413.html
right to left: http://apod.nasa.gov/apod/ap030310.html


(or the other way around)
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Re: Galaxy''s

Post by bystander » Thu Nov 06, 2008 7:47 pm

alexandrie wrote:Do all galaxy"turn the same direction studying the photograph"s thy all seem to turn from right to left :?:
The apparent direction of rotation is an illusion, dependent upon the side from which we view the galaxy. Some appear to rotate clockwise (cw) and some counterclockwise (ccw).

For more discussion, see Asterisk Café: Spiral galaxies.

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BMAONE23
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Re: Galaxy''s

Post by BMAONE23 » Thu Nov 06, 2008 9:56 pm

The spiral galaxies might all spin in the same direction IF galaxies can be fould to have a polar magnetic field associated with the entirety.
I guess a good question along those same lines would be Do spiral galaxies always spin in the same direction as their arms would indicate?

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Re: Galaxy''s

Post by bystander » Thu Nov 06, 2008 10:16 pm

BMAONE23 wrote:I guess a good question along those same lines would be Do spiral galaxies always spin in the same direction as their arms would indicate?
See The Spiral Arms of NGC 4622

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Re: Galaxy''s

Post by jesusfreak16 » Fri Nov 07, 2008 2:42 am

bystander wrote:
alexandrie wrote:Do all galaxy"turn the same direction studying the photograph"s thy all seem to turn from right to left :?:
The apparent direction of rotation is an illusion, dependent upon the side from which we view the galaxy. Some appear to rotate clockwise (cw) and some counterclockwise (ccw).

For more discussion, see Asterisk Café: Spiral galaxies.

I should have known that. :oops: (smacks self in face)
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spiral galaxies

Post by ironhead » Sat Jun 06, 2009 2:16 pm

why do they spin and do they all spin the same direction?

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Re: spiral galaxies

Post by bystander » Sat Jun 06, 2009 2:44 pm

ironhead wrote:why do they spin and do they all spin the same direction?
The direction of spin depends entirely upon your viewpoint. When seen from one side, they appear to spin clockwise. If you could get to the other side, they would appear to spin counter-clockwise. There are plenty of examples of both. Not all spiral galaxies spin in the same direction as their spiral (leading and trailing arms) and there is at least one with counter rotating spirals.

See APOD search for spiral galaxy.

As to why they spin, I'll leave that for someone with a better physics background.

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Re: spiral galaxies

Post by ironhead » Sat Jun 06, 2009 2:56 pm

thank you I was just curious

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Re: Spiral galaxies

Post by apodman » Sat Jun 06, 2009 3:08 pm

Do they all spin in the same direction with respect to the way the ends of their arms point? (Are the arms leading or trailing?) We think the arms are generally but not always trailing. Unknowns remain.

Why do they spin? Picture two objects approaching each other. As the get close, they are attracted by each other's gravity and three things can happen depending on speed and separation: (1) they collide; (2) they deflect and continue on their courses; or, (3) they go into orbit around each other. Objects that become gravitationally bound to each other are in category (3). The angular momentum of the resulting rotating system comes from the original linear momentum of the objects. This logic holds for systems of more than two objects as well. Systems collected together by gravity tend to rotate. An open question is where the objects got their linear momentum in various directions to begin with.

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Re: Spiral galaxies

Post by bystander » Sat Jun 06, 2009 3:13 pm

apodman wrote:Do they all spin in the same direction with respect to the way the ends of their arms point? (Are the arms leading or trailing?) We think the arms are generally but not always trailing. Unknowns remain.
See APOD: 2004 February 21 - The Spiral Arms of NGC 4622

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Re: Spiral galaxies

Post by harry » Sun Jun 07, 2009 12:58 am

G'day from the land of ozzzzzzzzz

THis is interesting

Galaxy Spin Vector Alignments in the Pisces-Perseus Supercluster
http://aas.org/archives/BAAS/v30n4/aas193/346.htm
[2.15] Galaxy Spin Vector Alignments in the Pisces-Perseus Supercluster
J. E. Cabanela, J. M. Dickey (U. Minnesota)

We use HI observations made using with the upgraded Arecibo 305M Telescope in August 1998 to obtain spin vectors for 54 edge-on galaxies in the Pisces-Perseus Supercluster. This represents the largest known sample of accurately measured spin vectors for galaxies outside the Local Supercluster. Analysis of the spin vector distribution was performed using the Kuiper statistic (a two-sided variant of the Kolmogorov-Smirnov statistic) to compare the observed spin vector distribution with Monte Carlo simulations.

Our initial analysis indicates that there is very strong evidence for spin vector alignments of galaxies with neighboring galaxies. We can rule out random galaxy spin vector orientations at the 99.5% confidence level. Galaxy alignments of this variety are likely an artifact of the history of angular momentum exchange between galaxies. This indicates that the alignment process is an ongoing, evolutionary effect of galaxy interactions.

Multiple Galaxy Collisions Surprise Hubble Astronomers
http://hubblesite.org/newscenter/archiv ... 9/45/text/
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Re: Spiral galaxies

Post by astrolabe » Sun Jun 07, 2009 10:47 pm

Hello All,

In June '08 or so there was a thread that discussed whether or not Galaxies tumble which was very interesting. I got curious, of course, an during a number of internet searches came across an international workshop taking place in Aug. '08 in Italy. I have not done any follow up on the conclusions or new approaches that may have come out of it but the idea of tumbling Galaxies WRT direction of spin also begs the question: are some right-side up or upside down or some other attitude with reference to us.

Awsome links!!
"Everything matters.....So may the facts be with you"-astrolabe

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Re: Spiral galaxies

Post by johnblanding » Thu Jun 11, 2009 2:20 am

Some where it must be written in great scientific detail, but simply, why are some or most galaxies pancake or disk shaped? Especially, if they are born as a result of an explosion, why did the resulting matter not go just everywhere or every direction? Thanks for answering these questions for those of us who know so little yet find space so interesting and mostly mystifying.

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Re: Spiral galaxies

Post by Chris Peterson » Thu Jun 11, 2009 4:43 am

johnblanding wrote:Some where it must be written in great scientific detail, but simply, why are some or most galaxies pancake or disk shaped? Especially, if they are born as a result of an explosion, why did the resulting matter not go just everywhere or every direction? Thanks for answering these questions for those of us who know so little yet find space so interesting and mostly mystifying.
Galaxies are not the product of any kind of explosion. They were formed when material came together by gravitational attraction. When that happens, conservation of angular momentum tends to result in motion on a plane. It's why galaxies are disc shaped, as well as why planets orbit stars on a plane.
Chris

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