How big is our Galaxy.

Okay.So what forms of information have reached us from the Galactic Center that we can definitely detect and measure?Visible light?X-Ray?Infrared?Others?

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Aslan is not a Tame Lion

You're right about light/life- that's what I get for studying biochem right before talking about astronomy!I've seen estimates for the position of the sun's place in the galaxy from 23,000 to 28,000 light years. Extrapolating the same error to the total size of the galaxy, I would assume it's about 100,000 +- 5,000 light years. Note that this is for the visible galaxy, and doesn't include the proposed dark matter halo, and stuff of that sort.

From Cosmic rays to post-Radio wavelengths and a small amount of neutrinos, but I won't count those.Basically the entire electromagnetic spectrum.

and all tend to agree that we are ~25,000 light years from the Galactic Center, and that our Galaxy is about 100,000 Light years across?

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Aslan is not a Tame Lion

Hi Jar, astronomy is all about order of magnitude so if we say 100,000, you can be fairly sure the real answer is somewhere between 10,000 and 1,000,000 At least, that is how it used to be... in my glory days we tended to think what's in a factor of 2?But to be fair, we're pretty good these days. I would suggest perhaps +/- 10,000 lyrs. As with terrestrial dating methods, we have a wide variety of distance measures which are compared, contrasted, and calibrated.[Edited once I had actually thought about this for 5 mins]This message has been edited by cavediver, 01-13-2006 04:21 PM

One of my favourite lessons I liked to teach was on how small the Universe is!For now I will just comment on the size of the Galaxy, the size of Andromeda, and their separation distance.Galaxy ~ 90,000 lyrsAndromeda ~ 110,000 lyrsSeparation = 2,200,000 lyrsThink about it... Andromeda is only 20 times further away, than it is across!!! Name some other distance structure in the physical hierarchy from planck scale to obs universe where there is such extreme proximity of objects.If you could turn down all the lights and turn up Andromeda's brightness, you would realise that it is four times wider than the moon on the night sky. How cool would that look?

So we are beginning have a pretty good idea about the size of our local neighborhood. But is there something analogous to a city that our neighborhood is within?

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Aslan is not a Tame Lion

Well, we have the Local Group, of which Andromeda and the Galaxy are two of the principal members, amongst a grouping of probably 30 or so galaxies. I think we're about 10,000,000 lyrs across. And we are part of a larger "cluster" and this cluster forms part of the Virgo supercluster.You are now into what we call the large-scale structure of the Universe. It is phenomenally well mapped out. I remember using a database of known galactic objects for a project back in 1991, and I look at similar databases today and they are incomparable... orders of magnitude more objects, with much greater certainty on distances.

So can you place some numbers and confidence levels on any of that?I gather from your post that the Local group is ~10,000,000 light years across.How far are we from the furthest edge of our local group?How do we know that?

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Aslan is not a Tame Lion

I can get back to this in more detail tomorrow, but for now...Andromeda and the Galaxy are pretty much in the centre, so we are 1 MLyr from the that centre, so around 4 MLyr from the edge, assuming a spherical boundary to the Local Group. Distances are probably around 10-20%.Cepheid variables have been mentioned as a distance measure and these are used extensively for close by galaxies, maybe even out to the edge of the Local Group... incredible that we use individual stars in other galaxies!The other methods I will leave till tomorrow as I'm getting nagged by the wife Have a good evening!

The Milky Way is about 5,000,000 light years from the edge of the local group.The local group is nested within the Virgo supercluster, which is a sphere with a radius of about 90,000,000 light years and fairly near the edge of the Virdo Supercluster, which contains the Virgo Cluster and the great attractor at the centre.The Virgo Supercluster lies near the Hydra and Centaurus superclusters
(which are unusual Superclusters in that they are composed of very dense clusters) and together they form a filament.
Near this filament lies a great wall, with the Coma Supercluster at its centre.This wall-then-filament structure repeats as you expand outwards through out the universe to a radius of 43 billion light years.This message has been edited by Son Goku, 01-13-2006 06:22 PM

SO for those of us that are dumber than a red brick, what does "This wall-then-filament structure" mean?

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Aslan is not a Tame Lion

Basically it means that the universe at the large scale is composed of threads of supercluster placed one after another along, basically, a line(filaments) and walls, which are literally giant walls made up of superclusters.A wall, on average contains maybe 10 million galaxies. A filament 1 million.
Occasionally there are gaps in this structure referred to as supervoids.

Galaxies in the universe can be visualized as frisbees moving randomly through space at an average distance apart of around 10 to 20 feet.--Percy

Just out of interest why Bible A&I - were you planning to use the info you got here in comparison with the views of Biblical Literalists or something?

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I wish I didn't know now what I didn't know then