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Yes, even the "extremely" distant galaxy clusters that lie 1-3 billion light years away and are visible in 18+ scopes are, cosmologically speaking, in our backyard.

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Well, I dunno. Three billion light-years is almost a quarter of the way to the edge of the observable universe. If I had to define our cosmic backyard, I'd pick the edge of the Virgo Supercluster as a natural boundary.

Here's one way of looking at that. Within the Virgo Supercluster, galaxy motions relative to the Milky Way are primarily due to local effects. Outside the Supercluster, they're primarily due to cosmic expansion.

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That is a way to look at it, and while I've read in some places we are falling towards the center of the Virgo Supercluster, a simple search on Simbad of redshift values for galaxies within that cluser does not support this assertion. I searched and found the redshifts of M61, M84, M87, M99, and M100 all were positive and consistant with a distance of 40-70MLY assuming a Ho of 70km/s/Mpc. The odd man out was M86, which had a redshift of z = -0.000901, or a closing speed of 270km/s. If we are indeed expanding away from the Virgo Cluster, then no doubt the combined gravity of it is lessening our velocity away from it, but the universal expansion would still be overwhelming gravity. I'll have to pull up more Virgo cluster members' redshifts and see for sure.

Three billion light years may be a quarter of the way back in time to the big bang, but the universe, by and large, looked and behaved pretty much like it does today- i.e., quasar density, metalicy, galaxy interactions and types, etc. Cosmologically speaking, it's our backyard.

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John T.
Auburn, AL
25" f/4.2 Dob
18" Obsession #701
4" Stellar Vue Achromat
8X56 Binos

Edited by tatarjj (07/30/08 01:14 PM)

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