APOD: Two-Armed Spiral Milky Way (2008 Jun 06)

[rigelan]

I think its incredible how we can take a side on view of the milky way, the perspective we get from this planet, and project a top view of it.

How do we REALLY know if there are two or four arms? It looks the same from the side. But we have all these little intricate models, and its pretty exciting to see.

http://apod.nasa.gov/apod/ap080606.html

Besides that, its great artwork.

[kjardine]

What's more, a lot of our view of what we could see is blocked by dust or the fact that some objects obscure other objects. The fact that astronomers can figure any patterns out of what we see is amazing!

Having said that, the new NASA image was designed to illustrate some specific conclusions from studying infrared images of the inner galaxy and, sadly, is not very consistent with what is known now about the outer galaxy.

I mention a few of the problems on my blog:

http://galaxymap.org/drupal/node/118

[Animation]

Harsh. I went to all the trouble to make this into a nice desktop and now apparently its junk. Oh well.

I guess I'll view it as one of those quaint ancient maps of the New World, I suppose.

Lewis

[Sputnick]

The symmetry is too perfect for nature .. nature is always slightly 'flawed' .. a little flattening of one side of the outer edge of the spiral perhaps, resulting from Time Funnels of course.

[iamlucky13]

It's too clean!

Of course, until someone actually heads north about 100,000 light years and takes a picture, we won't really be able to say exactly what it looks like, but none of the other galaxies are ever this clean looking.

Any volunteers? I'll let you borrow my camera, but you'll have to pay for gas on your own.


Kevin, I was slightly skeptical about your criticisms of the outer galaxy structure, but after reading your blog, I can definitely see how the Spitzer team's graphic could be inaccurate, since it is based on observations primarily of the area near the core.

Shucks...I was hoping Sagittarius would get to stay an arm. Someone's gotta root for the home team, even if the odds are against them.

[neufer]

It's too clean!

Of course, until someone actually heads north about 100,000 light years and takes a picture, we won't really be able to say exactly what it looks like, but none of the other galaxies are ever this clean looking.

Any volunteers? I'll let you borrow my camera, but you'll have to pay for gas on your own.

Anyone out there old enough (like me) to remember Science Fiction Theatre?

• Science Fiction Theatre
  Episode 1-36 Are We Invaded? 31 December 1955
  Pat O'Brien, Anthony Eustrel, Leslie Gaye
  
  <<"That which we do not understand sometimes causes apprehension." A reporter and the daughter of a respected astronomer, watching the stars one evening from their parked car, see what they consider a flying saucer. A stranger appears at the door of the car saying he too saw the light in the sky, and asks if he can be given a lift down the hill into town. Later, the astronomer refuses to believe the couple saw anything more than an optical illusion. To prove the existence of UFOs, the reporter films a documentary of witnesses, while the astronomer promptly demonstrates scientific explanations for each wittnesse's sightings. But the mysterious stranger has dropped off a photograph at the astronomer's lab- a photograph of our solar system taken from deep space. The stranger has disappeared, but left a forwarding address:
  Alpha Centauri, 4.5 light years from Earth.>>
  ---------------------------------------
  http://en.wikipedia.org/wiki/Science_Fiction_Theatre
  <<Science Fiction Theatre is a syndicated science fiction anthology series. It was produced in the United States by Ivan Tors and Maurice Ziv. Hosted by Truman Bradley, a 1940s film actor and former war correspondent, each episode introduced stories which had an extrapolated scientific, or pseudo-scientific emphasis based on actual scientific data available in the 1950s. The program concentrated on such concepts as space flight, robots, telepathy, flying saucers, time travel, and the intervention of extraterrestrials in human affairs.
  
  It ran from 1955 to 1957, with a total of 78 half hour episodes. It was also known as Beyond The Limits in second run syndication during the 1960s and alternatively as Science Fiction Theater.
  
  Science Fiction Theatre was a forerunner of similar shows, such as The Twilight Zone and The Outer Limits. Science Fiction Theatre was mentioned in the 1985 film Back to the Future starring Michael J. Fox (not to be confused with Michael Fox, a frequent actor in Science Fiction Theatre episodes) and Christopher Lloyd.
  
  Each episode was introduced by a stirring brass, string, and woodwind fanfare while the camera panned over a science laboratory.
  
  Host: How do you do, ladies and gentlemen? I'm your host, Truman Bradley.
  Let me show you something interesting
  
  Then Truman Bradley showed a simple scientific experiment which was usually related to the topic of that week's show. Mr. Bradley's demonstrations were often staged, but yielded results consistent with the outcome of true experiments. Due to the limited budgets and intense production scheduals of ZIV episodic television shows, most of the scientific, and not so scientific apparatus appears again and again as props with many different functions.>>

[NoelC]

The symmetry is too perfect for nature .. nature is always slightly 'flawed'

While many galaxies exhibit perturbation, presumably because of gravitational interaction with others, it's not impossible to imagine that our galaxy could be quite symmetrical, especially given that we have actual images of galaxies like these...

Click the pictures for descriptions and links to larger images.













-Noel

[henk21cm]

While many galaxies exhibit perturbation, presumably because of gravitational interaction with others, it's not impossible to imagine that our galaxy could be quite symmetrical, especially given that we have actual images of galaxies like these...

The link to this document is a bit tricky, since it links to a power point presentation. Most browsers do not know what to do with it. Nevertheless a ppt can be opened with Open Office 2.4. Sheet 60 gives an image of the structure of our galaxy in hydrogens universal wavelength of 21 cm. The image is a combination of data from radio telescopes on earths northern an southern hemispheres. The symmetry of our milky way in this image is rather low.

Some features can be recognized in the artist impression of APOD 2008-06-05. The very detailed and nicely curved spiral arms of that APOD are less easy to detect in the radio image. Sagittarius, Perseus, Outer and Scutum Centaurus arms are cleary visible. The radio image displays connections between the arms, which are missing in the IR based artist impression. Another difference is that the arms in the radio image are wound op more thight than in the APOD. Images similar to the radio image first appeared around 1950. A more recent image was found at http://physicsworld.com/cws/article/news/25014




The central section in the radio image is missing, since 21 cm mapping uses doppler shifts, which are too little to be detectable in a narrow bundle centered around the center of the galaxy. Another disadvantage is that the mapping depends on the assumed rotational model of our galaxy. Nevertheless the radio image is the result of measurements.

[NoelC]

Seems to me looking at a galaxy off in the distance face-on is pretty different from looking at one from the inside, from off to the side.

How far does galactic material rotate in 100,000 years?

What we can see from here, now, of the other side of our galaxy is many millenia out of date, while the stuff we can see locally is nearly current.

What an observer well above a galaxy would be more or less a "snapshot" of the galactic material all at the same time.

-Noel

[apodman]

One observer's snapshot is another's time-distributed view. Conveniently, the visual and gravitational snapshots for the observer within the galaxy are the same, and you can skip all the messy transformations if gravity and understanding the rotation is what you're looking for. The distant z-axis observer's "snapshot" is not objective reality anyway, rather just another observer with a relative view.

[NoelC]

I don't buy that at all.

The arms near us could progress a great distance by the time the light from the arms on the other side of the galaxy reach us. This will bear greatly on whether it appears symmetrical to us right here and now.

Indeed, it is likely relativistic forces - the propagation of gravity at the speed of light - that are causing the structure in the arms in the first place.

If you're not willing to envision/imagine a galaxy full of stuff all in a particular place at a particular moment in time (for a distant observer high up on the Z axis), then you had better not even try to think about stuff on that scale. Nothing is where it appears to be for any given observer. However, imagining/modeling where it REALLY is all at the same time could yield a better understanding of cosmic physics.

-Noel

[apodman]

We're actually on the same thought here, and you're mostly expressing it better than I, but Einstein is still spinning over your use of "REALLY" and "same time". That's all.

[apodman]

To be clear, I agree on the value of modeling from the viewpoint of a preferred objective observer even though there is none.

[bystander]

While the caption talks of two spiral arms, the picture depicts four. Although there are two major arms with better definition (the Scutum-Centaurus and Perseus arms). There are also two less defined minor arms (the Sagitarius and Norma arms). They also spiral out from the central bar.

APOD: 2008 June 6 - Two-Armed Spiral Milky Way

Two earlier artistic interpretations on apod show two arms with branches.

APOD: 2005 August 25 - Barred Spiral Milky Way
APOD: 2005 January 4 - Milky Way Illustrated

[dfranco]

The picture showing the possible z-axis view of the Milky Way has the text that says something to the effect "Astronmers believe that Sol is about a third away from the edge of the galaxy on the Orion Spur. However, if one mouse overs the image, it appears that Sol is about a third away from the centre of the galaxy. Which is it?

Also, according to http://viewzone.com/milkyway.html solar system appears closer to the edge of the galaxy and the solar system is not from the Milky Way!

Comments?

[bystander]

The picture showing the possible z-axis view of the Milky Way has the text that says something to the effect "Astronmers believe that Sol is about a third away from the edge of the galaxy on the Orion Spur. However, if one mouse overs the image, it appears that Sol is about a third away from the centre of the galaxy. Which is it?

The "mouse-over" coordinates are sol-centric. That would place Sol somewhere between a half and a third of the way in.

Also, according to http://viewzone.com/milkyway.html solar system appears closer to the edge of the galaxy and the solar system is not from the Milky Way!

Interesting! Does the relative motion of Sol support this SagDEG capture theory?

[iamlucky13]

Seems to me looking at a galaxy off in the distance face-on is pretty different from looking at one from the inside, from off to the side.

How far does galactic material rotate in 100,000 years?

What we can see from here, now, of the other side of our galaxy is many millenia out of date, while the stuff we can see locally is nearly current.

What an observer well above a galaxy would be more or less a "snapshot" of the galactic material all at the same time.

-Noel

It's not that bad. The sun has a period around the galaxy of about 225 million years. The objects that we look out upon aren't too far from where they appear to be. Also, it's possible, although I don't know if the Spitzer team did this, to approximate where they should be, based either on assumed or measured trajectories.

Bystander, the discrepancy in the caption is because astronomers are now considering the smaller "arms" to be deserving a lesser categorization. If you thought Pluto getting dropped from the planets was bad...now they're demoting the entire Sagittarius arm!

[BMAONE23]

I guess living elsewere in the Galaxy could cost you an arm

[Arramon]

Only thing I'm wondering about if our solar system is from the Sagittarius Dwarf galaxy, does the composition of our sun match the composition of suns from the 'other' galaxy merging with the Milky Way? It says they focused on M type stars, and the 'other' galaxy popped out at them.



How are they so sure our sun is from that galaxy and not the Milky Way? And with the galaxy being consumed having such an altered shape because of the Milky Way, wouldn't the Milky Way have some distortions of its own from the smaller galaxies merging with it?

None of the newer artist impressions of the Milky Way incorporate all the galaxies that are merging together (SMC, LMC, Sagittarius, Milky Way, etc).

[harry]

G'day from the land of oz

Here down under we use maps

Atlas of the universe
http://www.atlasoftheuniverse.com/

INTERACTIVE SPACE MAP
http://www.bbc.co.uk/science/space/playspace/spacemap/


Chandra Sky map
http://chandra.harvard.edu/photo/map/


News Release - heic0701: First 3D map of the Universe's Dark Matter scaffolding
http://www.spacetelescope.org/news/html/heic0701.html


Sloan mapping of the universe
http://www.sdss.org/news/releases/20...rspectrum.html

[makc]

One observer's snapshot is another's time-distributed view.

correct premise, but the conclusion is weird at least. visual snapshot not equals to equal-time snapshot I assume you were talking about.

someone looking at galxy from top would still be a bit closer to core (or some other part), and you would have to adjust for that. but someone inside the galaxy is subject to much more substantial adjustments.

[harry]

G'day from the land of ozzzzzz


Is someone going on holidays, is this a room with a view window.

[d2386n]

This 'map' of the Milky Way is impressive. I think it would be great to have a real pic of the Milky Way disk. If we flung a camera payload straight up through the disk as fast as we could move it, I wonder how many centuries it would be before we could get a picture looking back at the disk of the Milky Way ?

[BMAONE23]

Given
Light travels at 186,000 mps
186k x 60 sec x 60 min x 24 h = 16,070,400,000 miles per day
or 5,865,696,000,000 miles per year.
You would likely need to travel 25,000ly above the galactic plane to see the entire galaxy.
5,865,696,000,000 x 25,000 = 146,642,400,000,000,000 miles to travel.
Our current fastest probe is traveling at appx 56k mph = 490,560,000 miles per year. A that rate it would take 298,928,571 years to reach 25000 ly above the galactic plane then another 25000 (+48,000) ly for the image to reach us at which time we will have circled the entire galaxy once (+18% for the 48,000 ly distance traveled after completing 1 galactic orbit.

We would actually complete 1 galactic orbit 48000 years before the probe arrived at its vantage point.

So your answer is: It would take almost 300 million years to receive a decent image given the state of our current technology.
Even if we could get instantly there, the image would still take 25000 years to reach us

[apodman]

Obviously we should tune in to a signal from a probe that someone else launched long ago.