Starship Asterisk*

The Universe Nearby

Explanation: What does the universe nearby look like? This plot shows nearly 50,000 galaxies in the nearby universe detected by the Two Micron All Sky Survey (2MASS) in infrared light. The resulting image is anincredible tapestry of galaxies that provides limits on how the universe formed and evolved. The dark band across the image center is blocked by dust in the plane of our own Milky Way Galaxy. Away from the Galactic plane, however, each dot represents a galaxy, color coded to indicate distance. Bluer dots represent the nearer galaxies in the 2MASS survey, while redder dots indicating the more distant survey galaxies that lie at a redshift near 0.1. Named structures are annotated around the edges. Many galaxies are gravitationally bound together to form clusters, which themselves are loosely bound into superclusters, which in turn are sometimes seen to align over even larger scale structures.

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Seeing everything in the 'small' like that, it's almost hard to imagine the 'Bigness' of what it represents.

How "nearby"? I don't have a PhD in Astronomy, so don't understand all the techie talk.
Can you give me an idea in terms of millions of lightyears? Thanks.

Mactavish wrote:How "nearby"? I don't have a PhD in Astronomy, so don't understand all the techie talk.
Can you give me an idea in terms of millions of lightyears? Thanks.

bystander wrote: http://asterisk.apod.com/viewtopic.php?t=23760&p=149149

CfA wrote:Today, astronomers unveiled the most complete 3-D map of the local universe (out to a distance of 380 million light-years) ever created. Taking more than 10 years to complete, the 2MASS Redshift Survey (2MRS) also is notable for extending closer to the Galactic plane than previous surveys - a region that's generally obscured by dust.

Alton Arp, an astronomer of note, showed how we measure distance using redshift techniques can be seriously questioned. If so the current map of galaxies shown is not an exact map, but an estimation that may be flawed. If we completely understood the structure & workings of the Universe, why bother with being a lowly astronomer?

Nearby Universe?!? My dictionary defines universe as "All existing matter and space considered as a whole; the cosmos." Has this definition 'slipped' or is it misused? I have heard terms like 'Super-Group' and "Super Bubble" used for groupings of galaxies but I thought that Universe was the ultimate, a unique term referring to EVERYTHING!

If I say "nearby neighbourhood" I will be understood to mean only that portion of my neighbourhood which is relatively close to me, and not the entire area that might be my full neighbourhood. Language is not bound in a straitjacket; it is flexible and capable of great subtlety.

Rob

would be great to have this data in rotatable, zoomable 3d.

I just did some primary school calculations on the back of an envelope and reckon that map represents a little under 2% of the whole - is that about right?

you can get some stunning photos from 2mass image gallery! Might be worth downloading a shortcut. http://www.ipac.caltech.edu/2mass/gallery/

davidgin50 wrote:
I just did some primary school calculations on the back of an envelope and reckon that map represents a little under 2% of the whole - is that about right?

[list]I get more like ~ 0.001% [/list]

http://apod.nasa.gov/apod/ap071107.html wrote:
Galaxies within one billion light years
= a redshift of about 0.1

http://en.wikipedia.org/wiki/Observable_universe wrote:
<<The current comoving distance to the particles which emitted the CMBR, representing the radius of the visible universe, is calculated to be about 14.0 billion parsecs (about 45.7 billion light years), while the current comoving distance to the edge of the observable universe is calculated to be 14.3 billion parsecs (about 46.6 billion light years).>>

garry wrote:Alton Arp, an astronomer of note, showed how we measure distance using redshift techniques can be seriously questioned. If so the current map of galaxies shown is not an exact map, but an estimation that may be flawed. If we completely understood the structure & workings of the Universe, why bother with being a lowly astronomer?

Halton Arp was well respected, but has generally lost a good deal of that because of his refusal to adapt his ideas to new evidence- a very unscientific way of thinking. Nothing that Arp proposed regarding redshift has held up to close examination, yet Arp continues to try bending the data to fit his ideas, not the other way around. In fact, virtually nobody seriously questions the utility of the redshift-distance relationship, and it is unlikely that this map is flawed in some fundamental respect.

Surely, nobody is suggesting that we completely understand the structure and workings of the Universe? The data contained in this image is useful for placing bounds on some of the unknowns, which in astronomy, is one of the most common ways that knowledge advances.

neufer wrote:I get more like ~ 0.001%

And of course, that's just for the observable Universe. If we consider the entire Universe, it's almost certainly a tiny fraction even of that... if not an infinitesimal one!

neufer wrote:I get more like ~ 0.001%

That's just using a simple ratio of the radii (radiuses?). Since we are dealing with volume, shouldn't that be cubed?

bystander wrote:

neufer wrote:
I get more like ~ 0.001%

That's just using a simple ratio of the radii (radiuses?). Since we are dealing with volume, shouldn't that be cubed?

The radii are in a ratio of 1 to 46.

The volumes are in a ratio of 1 to 46³.

what's the scale of today's map, is it 1:1,000,000,000,000,000,000,000,000,000,000

neufer wrote:The radii are in a ratio of 1 to 46.

The volumes are in a ratio of 1 to 46³.

For this, the radii are in a ratio of 380 × 10⁶ to 46.6 × 10⁹

CfA wrote:… (out to a distance of 380 million light-years) …

bystander wrote:

neufer wrote:The radii are in a ratio of 1 to 46.

The volumes are in a ratio of 1 to 46³.

For this, the radii are in a ratio of 380 × 10⁶ to 46.6 × 10⁹

CfA wrote:… (out to a distance of 380 million light-years) …

APOD Robot wrote: The Universe Nearby

Explanation: Bluer dots represent the nearer galaxies in the 2MASS survey,
while redder dots indicating the more distant survey galaxies that lie at a redshift near 0.1 [~ 10⁹ lyrs]. >>

Ok, I give up. Calling myself an insignificant one is far far too generous. Perhaps I should just sit down, preferably in Brazil, with an ice cold one in my hands, wait for Eta Carinae to shower me with whatever cosmic wave it wants to and always have access to APOD. and some farofa.

Wolf kotenberg wrote:
Ok, I give up. Calling myself an insignificant one is far far too generous. Perhaps I should just sit down, preferably in Brazil, with an ice cold one in my hands, wait for Eta Carinae to shower me with whatever cosmic wave it wants to and always have access to APOD. and some farofa.

Wolf kotenberg wrote:Ok, I give up. Calling myself an insignificant one is far far too generous. Perhaps I should just sit down, preferably in Brazil, with an ice cold one in my hands, wait for Eta Carinae to shower me with whatever cosmic wave it wants to and always have access to APOD. and some farofa.

Let's have a convention. Where in Brazil?

If the speed of light is changing (in my mind another way to think of the "expansion" of space-time - am I way off base?), then is it really meaningful to think in terms of distance? Not to mention that the distances are virtually unimaginable anyway. I like that this map is presented in % of C as opposed to trying to describe things in terms of distance.

-Noel

NoelC wrote:If the speed of light is changing (in my mind another way to think of the "expansion" of space-time - am I way off base?)...

I do think that's off base. The expansion has no connection with c, but only shifts the wavelength as the intervening space expands.

...then is it really meaningful to think in terms of distance?

There is some kind of meaning there, but perhaps it isn't so useful. Cosmologists generally look at z, the redshift, as the fundamental unit, and it isn't usually felt necessary to convert this to a distance- except in press releases <g>.

Not to mention that the distances are virtually unimaginable anyway.

Are they? I don't find it difficult at all to think in terms of billions of light years. These seem like natural and easy units for measuring the Universe. It's no different than thinking in fractions of nanometers for many atomic scale examples. I think the problem comes when people try to tie together units that are radically different, like directly comparing the distance to the supermarket to the distance across the observable Universe. But there's no need to do that.

I like that this map is presented in % of C as opposed to trying to describe things in terms of distance.

The map is not really showing a percentage of c. That would be a velocity. The map is showing redshift, which is a ratio of the apparent recessional velocity to c- a unitless value.

I decided while sitting in brazil sipping on a cold one, that no matter where I am, the universe is about 14 billion light years old.