APOD: M33: Triangulum Galaxy (2010 Dec 03)

[APOD Robot]

M33: Triangulum Galaxy

Explanation: The small, northern constellation Triangulum harbors this magnificent face-on spiral galaxy, M33. Its popular names include the Pinwheel Galaxy or just the Triangulum Galaxy. M33 is over 50,000 light-years in diameter, third largest in the Local Group of galaxies after the Andromeda Galaxy (M31), and our own Milky Way. About 3 million light-years from the Milky Way, M33 is itself thought to be a satellite of the Andromeda Galaxy and astronomers in these two galaxies would likely have spectacular views of each other's grand spiral star systems. As for the view from planet Earth, this sharp, detailed image nicely shows off M33's blue star clusters and pinkish star forming regions that trace the galaxy's loosely wound spiral arms. In fact, the cavernous NGC 604 is the brightest star forming region, seen here at about the 4 o'clock position from the galaxy center. Like M31, M33's population of well-measured variable stars have helped make this nearby spiral a cosmic yardstick for establishing the distance scale of the Universe.

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[owlice]

This lovely image appeared earlier on Asterisk here: http://asterisk.apod.com/vie ... 79#p137389

[orin stepanek]

Hubble Image from Wikipedia

Click to view full size image

Amazing view of NGC 604.

[neufer]

Future precessional movement

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Triangulum + γ = the constellation known as [sup]MUL[/sup]APIN

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<<In the Babylonian star catalogues, Triangulum together with γ And formed the constellation known as ^MULAPIN "The Plough". It is notable as the first constellation listed in the pair of tablets containing the canonical star lists compiled around 1000 BC, which are thus known as the MUL.APIN by their incipit. The Plough was the first constellation of the "Way of Enlil", i.e. northernmost quarter of the Sun's path [containing 33 stars or constellations], corresponding to the 45 days on either side of summer solstice.

An early name of the constellation was Sicilia, because Ceres, patron goddess of Sicily, was claimed to have begged Jupiter that the island be placed in the heavens.>>

<<MUL.APIN is the conventional title given to a Babylonian compendium that deals with many diverse aspects of Babylonian astrology. It is in the tradition of earlier star catalogues, the so-called Three Stars Each lists, but represents an expanded version based on more accurate observation, likely compiled around 1000 BC. The text lists the names of 66 stars and constellations and further gives a number of indications, such as rising, setting and culmination dates, that help to map out the basic structure of the Babylonian star map.

The catalogue is the direct predecessor of the classical Neo-Babylonian zodiac as it was developed in the 7th century BC, which was in turn received by Eudoxus of Cnidus in the 4th century, giving rise to Hellenistic astrology.

The text is preserved in a 7th century BC copy on a pair of tablets, named for their incipit, corresponding to the first constellation of the year, MULAPIN "The Plough", identified with Triangulum plus Gamma Andromedae. The latest copies of Mul-Apin are currently dated to around 300 BC.

Astrophysicist Bradley Schaefer claims that the observations reported in these tablets were made in the region of Assur at around the year 1370 BC.

The text runs to two tablets and possibly a third auxiliary tablet. The first tablet is the most important resource for any potential reconstruction of the Babylonian star map as its various sections locate the constellations in relation to each other and to the calendar. Tablet 1 has six main sections:

• * All the major stars and constellations are listed and organised into three broad divisions according to celestial latitude allocating each star to three paths:
  • o the northern path of Enlil containing 33 stars or constellations
    o the presumably equatorial path of Anu containing 23 stars or constellations, and
    o the southern path of Ea containing 15 stars or constellations,
    Most of these stars and constellations are further attributed to a variety of Near Eastern deities.
  * The heliacal rising dates of 34 stars and constellations are given according to the 360-day ‘ideal’ calendar year.
  * Lists of stars and constellations that rise and set at the same time.
  * The number of days between the risings of various stars and constellations.
  * The stars and constellations that rise and culminate at the same time.
  * The stars on the path of the moon, being the major constellations close to the ecliptic, which includes all the Babylonian forerunners to the zodiac constellations.

Even though the Babylonians used a luni-solar calendar, which added an occasional thirteenth month to the calendar, Mul-Apin, like most texts of Babylonian astrology, uses an ‘ideal’ year composed of 12 ‘ideal’ months each of which was composed of an ‘ideal’ 30 days. In this scheme the equinoxes were set on the 15th day of the first and seventh month, and the solstices on the 15th day of the fourth and tenth month.>>

[Magellan Starswarm]

I have been using mostly APOD Archive, a curious mind and wandering heart to educate meself for a while so kindly forgive my um...you know, ignorance. Do all galaxies spin in the same direction as the great spiral egg we call the Milky Way?

[bystander]

The apparent direction of rotation of galaxies depends entirely upon which side we see them from. If you were to view a galaxy that appears to spin clockwise from the opposite side, it would then appear to spin counter-clockwise.

http://asterisk.apod.com/vie ... =8&t=14572

[neufer]

Do all galaxies spin in the same direction as the great spiral egg we call the Milky Way?

Spiral arms are essentially fixed standing waves and stars orbit into the concave side of these arms and come out the convex side of these arms.

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[owlice]

Spiral arms are essentially fixed standing waves and stars orbit into the concave side of these arms and come out the convex side of these arms.

So the arms aren't rotating, the galaxy as a whole doesn't rotate? Stars pass through them as they rotate around the galactic center; the composition of the arms change as stars move through them, is that right?

[neufer]

Spiral arms are essentially fixed standing waves and stars orbit into the concave side of these arms and come out the convex side of these arms.

So the arms aren't rotating, the galaxy as a whole doesn't rotate? Stars pass through them as they rotate around the galactic center; the composition of the arms change as stars move through them, is that right?

Basically.

The arms no doubt slowly evolve in some fashion but how (or how fast) isn't quite clear.

[owlice]

Thanks, Yogi!

[nstahl]

What on earth would generate a standing wave in a galaxy? In a stream it's a rock. In a wind instrument it's the resonating chamber. Or it can be waves of equal amplitude and opposite velocity. None of those seems likely to apply in a galactic disc.

Also, given the time scales involved, have we observed galaxies long enough to be sure the spiral arms are standing waves?

[Chappy]

From what I understand, and it is limited, Galaxies do rotate, but unlike how you would think. Since the laws of physics state that a spinning object rotates faster the closer you get to it's rotational center, you would expect Galaxies to basically spin themselves to pieces since they are not a solid piece of matter, and the outer arms would lag so far behind that it would be a jumbled mess in no time....but they don't.
They spin at almost exactly the same rate at the center as they do at the edge, meaning that something is basically holding it all together as one solid kinda piece.
The leading hypothesis of course, is that space & time constitute a fabric like substance due to dark matter/energy, and because of being suspended, so to speak, in this fabric, the entire Galaxy spins as a single object while individual objects within the galaxies are doing there own thing...kinda...in a way...sorta.
If we look at it as similar to, say a bedsheet, then it's easier to see how such standing waves could occur.

Did I get that right?
If not, just ignore this blathering idiot over in the corner..

[neufer]

From what I understand, and it is limited, Galaxies do rotate, but unlike how you would think. Since the laws of physics state that a spinning object rotates faster the closer you get to it's rotational center, you would expect Galaxies to basically spin themselves to pieces since they are not a solid piece of matter, and the outer arms would lag so far behind that it would be a jumbled mess in no time....but they don't.

They spin at almost exactly the same rate at the center as they do at the edge, meaning that something is basically holding it all together as one solid kinda piece.

Unlike planets around a sun, stars orbit at almost exactly the same velocity at the center as they do at the edge.

However the spiral arms are density waves that don't get all wound up like the stars themselves.

Explanation of spiral galaxy arms made up of elliptical orbits.

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The first acceptable theory for the spiral structure
was devised by C. C. Lin and Frank Shu in 1964.

* They suggested that the spiral arms were manifestations of spiral density waves.

* They assumed that the stars travel in slightly elliptical orbits and that the orientations of their orbits is correlated i.e. the ellipses vary in their orientation (one to another) in a smooth way with increasing distance from the galactic centre. This is illustrated in the diagram. It is clear that the elliptical orbits come close together in certain areas to give the effect of arms. Stars therefore do not remain forever in the position that we now see them in, but pass through the arms as they travel in their orbits.

[Chris Peterson]

They spin at almost exactly the same rate at the center as they do at the edge, meaning that something is basically holding it all together as one solid kinda piece.
The leading hypothesis of course, is that space & time constitute a fabric like substance due to dark matter/energy, and because of being suspended, so to speak, in this fabric, the entire Galaxy spins as a single object while individual objects within the galaxies are doing there own thing...kinda...in a way...sorta.

Half right. Nothing to do with the fabric of space or dark energy. The explanation involves the presence of a large amount of dark matter, which is like any other matter in terms of its gravitational effects, but doesn't interact with electromagnetic radiation, so is essentially invisible to us.

[Don Lund]

The explanation involves the presence of a large amount of dark matter, which is like any other matter in terms of its gravitational effects, but doesn't interact with electromagnetic radiation, so is essentially invisible to us.

Umm, OK. But if DM behaves like any other matter in terms of its gravitational effects, why doesn't it orbit the galactic center faster near the center than it does much further out? My idiot impression is that DM is sort of gluing the galaxy together so that it rotates in a semi-rigid way, and somehow that just doesn't seem to make sense...

Don Lund

[nstahl]

Thank you neufer. That's fascinating. It explains how density waves could occur but brings up questions of how such correlated orbits came about.

[nstahl]

Earlier, Magellan Starswarm asked whether all the spiral galaxies lined up the same way. Here's something pertinent from neufer's Wikipedia article on Spiral Galaxies:

Alignment of spin axis with cosmic voids
Recent results suggest that the orientation of the spin axis of spiral galaxies is not a chance result, but instead they are preferentially aligned along the surface of cosmic voids. That is, spiral galaxies tend to be oriented at a high angle of inclination relative to the large-scale structure of the surroundings. They have been described as lining up like "beads on a string," with their axis of rotation following the filaments around the edges of the voids.

[Chris Peterson]

Umm, OK. But if DM behaves like any other matter in terms of its gravitational effects, why doesn't it orbit the galactic center faster near the center than it does much further out? My idiot impression is that DM is sort of gluing the galaxy together so that it rotates in a semi-rigid way, and somehow that just doesn't seem to make sense...

It is orbiting faster near the center. The dark matter halo is a lot larger, and a lot more massive, than the ordinary matter. So the entire gravitational environment around a galaxy is altered by its presence. In particular, the DM halo is spherical, and for any visible component of the galaxy, most of the mass will be outside its orbital radius.

The dark matter isn't strictly gluing anything together, although the analogy isn't too bad. And a galaxy doesn't rotate as if it were rigid- the inner stars orbit faster than the outer ones. It's just that the difference in rotational velocity is smaller than can be explained if the visible mass is all there is.

[neufer]

Explanation of spiral galaxy arms made up of elliptical orbits.

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Thank you neufer. That's fascinating.

It explains how density waves could occur but brings up questions of how such correlated orbits came about.

(Assuming that this is basically the correct model) it is possibly that this is a quasi-stable mode for all these elliptical orbits in that the asymmetrical attraction of the spiral arms cause all of the elliptical orbits to precession clockwise at a relatively constant spin rate.

The clockwise precession rate would define the rotation rate of the spiral arms themselves.

[Don Lund]

Umm, OK. But if DM behaves like any other matter in terms of its gravitational effects, why doesn't it orbit the galactic center faster near the center than it does much further out? My idiot impression is that DM is sort of gluing the galaxy together so that it rotates in a semi-rigid way, and somehow that just doesn't seem to make sense...

It is orbiting faster near the center. The dark matter halo is a lot larger, and a lot more massive, than the ordinary matter. So the entire gravitational environment around a galaxy is altered by its presence. In particular, the DM halo is spherical, and for any visible component of the galaxy, most of the mass will be outside its orbital radius.

The dark matter isn't strictly gluing anything together, although the analogy isn't too bad. And a galaxy doesn't rotate as if it were rigid- the inner stars orbit faster than the outer ones. It's just that the difference in rotational velocity is smaller than can be explained if the visible mass is all there is.

Thanks, Chris! I don't understand the dynamics here, out of my pay grade, I guess. To bring this down to Earth a bit: If a bunch of Jupiter-size planets were added to the solar system, orbiting at Mars or beyond, would the Earth orbit the sun more slowly? Thanks again...

Don Lund

[Beyond]

Thanks, Yogi!

Baseball had it's Yogi Berra - and now i see Apod has a Yogi we have to beara. Lets hope he doesn't 'strike-out' toooo much

[neufer]

Baseball had it's Yogi Berra - and now i see Apod has a Yogi we have to beara.
Lets hope he doesn't 'strike-out' toooo much

Yogi Berra quotes:

A nickel ain't worth a dime anymore.

All pitchers are liars or crybabies.

Always go to other people's funerals, otherwise they won't come to yours.

Baseball is ninety percent mental and the other half is physical.

Congratulations. I knew the record would stand until it was broken.

Even Napoleon had his Watergate.

Half the lies they tell about me aren't true.

He hits from both sides of the plate. He's amphibious.

How can you think and hit at the same time?

I always thought that record would stand until it was broken.

I just want to thank everyone who made this day necessary.

I never blame myself when I'm not hitting. I just blame the bat and if it keeps up, I change bats.
After all, if I know it isn't my fault that I'm not hitting, how can I get mad at myself?

I never said most of the things I said.

I think Little League is wonderful. It keeps the kids out of the house.

I wish I had an answer to that because I'm tired of answering that question.

I'm a lucky guy and I'm happy to be with the Yankees. And I want to thank everyone for making this night necessary.

I'm not going to buy my kids an encyclopedia. Let them walk to school like I did.

If people don't want to come out to the ball park, nobody's gonna stop 'em.

If the world was perfect, it wouldn't be.

If you ask me anything I don't know, I'm not going to answer.

If you come to a fork in the road, take it.

If you don't know where you are going, you might wind up someplace else.

In baseball, you don't know nothing.

In theory there is no difference between theory and practice. In practice there is.

It ain't over till it's over.

It ain't the heat, it's the humility.

It gets late early out there.

It was impossible to get a conversation going, everybody was talking too much.

It's like deja-vu, all over again.

It's pretty far, but it doesn't seem like it.

Little League baseball is a very good thing because it keeps the parents off the streets.

Nobody goes there anymore. It's too crowded.

Slump? I ain't in no slump... I just ain't hitting.

So I'm ugly. So what? I never saw anyone hit with his face.

The future ain't what it used to be.

The other teams could make trouble for us if they win.

The towels were so thick there I could hardly close my suitcase.

There are some people who, if they don't already know, you can't tell 'em.

We have deep depth.

We made too many wrong mistakes.

When you arrive at a fork in the road, take it.

You better cut the pizza in four pieces because I'm not hungry enough to eat six.

You can observe a lot by just watching.

You should always go to other people's funerals, otherwise, they won't come to yours.

You wouldn't have won if we'd beaten you.

You've got to be very careful if you don't know where you are going, because you might not get there.

[bystander]

Yogi Berra quotes:

I think he was George W. Bush's speech writer.

[Chappy]

All fascinating stuff!
Thanx for that chart/explanation neufer, it does make some sense how that can work all together to create a rotation.

It is amazing to think that what we see optically is only a small fraction of the mass needed to make all the gravitational computations work. I keep thinking...why can't we find some sort of proof (other than mathematically that is), for the presence of dark matter or energy? We have entered the realm of space itself in our quest for knowledge, yet this major part of our universe is untouchable, undetectable to our present sensor capabilities, we can't detect it in any way except by observing how it massively alters how visible matter behaves. We must almost be living literally in a soup of the stuff, yet we know relatively nothing about it.
I also know we "can" currently measure the distribution of DM using grav-lensing, but that's nothing like actually touching the stuff. If it has such a high mass, why can't we scoop some up and study it?

Damn cool stuff to contemplate IMO, but I sure wish we could bring a bottle of it back from our intra-solar journeys someday and study the stuff.
I know that's talking nonsense in today's world, but just maybe someday we'll be able to actually touch it.

The Yogi quotes are a nice touch too LOL

[Beyond]

Neufer-neufer, He's our man; if he can't find information on it, no-one can. Inner-space outer-space really doesn't matter, He'll get you the information quicker than a Mad Hatter. It may not be quite what you were looking for, but then again - it's never a bore. He'll throw at you facts and figures and even a little folk-lore. His loquacious way is known far and wide and from it HE cannot hide. Though he may speak from many a name, the end result is always the same.
There-fore today, in his Honor, i present a new term -- Neufermation. You could say it is very Artsy.