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Posted by Nicholas on November 18, 2002 23:25:23 UTC

"They show the earth to be the center of the portion of the universe that we can see- almost by definition since every thing is expanding away
from us. "

That's exactly right. The only way the Earth would not be the center is if we were to observe a boundary somewhere. If you sit inside of a sphere but can't see the edges, there is no way to find a geometrical center.

One of the other centers that Mike mentioned is kind of observable, center of velocity. The reason I say kind of is because you need to see the whole universe in order to find any kind of "absolute" center, but you can see local centers. For example, the velocity center in the regions of space surrounding the local group of galaxies is located somewhere in the Virgo cluster. Galaxies outside of this region, however, will be heading towards some other center.

Also, you can map the distribution of galaxies throughout the observable universe by knowing only relative distances rather than absolute distances. Current theories say that you can get relative distances from the cosmological redshift. Using this, we can map galaxies throughout time and space. We find that clusters of galaxies tend to be located at the intersections of gigantic filaments, forming a sort of cosmic web.

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