Galaxy= Cluster of stars
Galactic Cluster= Cluster/ group of galaxies- example: The COMA cluster
Source: http://www.damtp.cam.ac.uk/research/gr/public/images/gal_coma.gif
Galactic Supercluster= Cluster of galactic clusters- group of galactic clusters. In general, these superclusters often involve galaxies arranged together in joined filaments or bands, that are arranged as though randomly throughout empty space. Example: Virgo supercluster
Source: http://www.fas.org/irp/imint/docs/rst/Sect20/M33.jpg
E6.2: Explain the red-shift of light from distant galaxies
It was found that not only is the light from all galaxies red-shifted, but the ones that are furthest away are shifted by more, which implies that the universe is EXPANDING.
Hubble's Law: The relationship between the distance of the galaxy and how fast it appears to be moving.
BALLOON ANALAGY- when you blow a balloon with small pieces of paper stuck on it, you can see that the ones further away expand faster (get further away, quicker). However, the pieces of paper do not get bigger- thus the actual GALAXIES don't get bigger.
On a small scale, gravity is strong enough to hold objects together, but on larger scales, expansion takes over, and causes everything to move apart from each other. It has been found that dark energy has been causing the universe to expand at an accelerating rate.
Hubble's law is true everywhere in the universe; either nowhere is the centre of our universe, or everywhere is.
It is the expansion of space, as opposed to the motion of the galaxies through space, that results in the galaxies' relative velocities. This is because: on a large scale, expansion causes everything to move apart- it is the expansion of space and not just the motion of the galaxy, because every galaxy, in every direction tis moving away from us. From any point in the universe, it can be observed that all galaxies are moving away. Space itself is expanding.
Source: Study Guide- Tom Kirk
E6.3: Solve problems involving red-shift and the recession speed of galaxies.
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