Astronomy 100 -- Hubble's Law and Large Scale Structure
DISTANCES TO DISTANT GALAXIES
For measuring distances to galaxies greater than 5 Megaparsecs
(15 Million LY) away, astronomers
use the HUBBLE LAW.
THE HUBBLE LAW
"The More Distant an Object is,
the Greater is its Recessional Speed."
The Hubble Law is a linear relation between how fast an object is
receding from us and the distance to that object (such as a distant galaxy).
For ALL distant objects,
or this can be written as
Speed = Hubble Constant x Distance.
The Hubble Constant, H, is a speed divided by a distance and
astronomers use units of kilometers per second per Megaparsec,
written as km/s/Mpc or km s-1 Mpc-1.
The VALUE of the Hubble Constant ranges between 50 and 90
km s-1 Mpc-1, with the most recent
"best" determination being
H = 75 km s-1 Mpc-1.
Outside of clusters of galaxies, the overall galaxy
distribution is not smooth. Below is a model of a LARGE
VOLUME OF SPACE. This cube is approximately 500 Mpcs on a side!
The Universe on a large scale looks like a sponge!
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