Use these questions to test your understanding. If you get them wrong, you will be linked back to the relevant part of the notes. 

Be sure you study them thoroughly (don't just get a quick fix for your mistake) so your overall understanding is improved.

1. Galaxies are distributed

   a. uniformly through space

   b. in vast sheets and filaments that make a structure a little like soap bubbles

   c. in clusters and groups

   d. in rings around the Milky Way

   e. both b. and c.

2. The mass of a cluster of galaxies

   a. is entirely from its galaxy members

   b. includes a significant part from very hot gas and even more from dark matter

   c. results in broadening the spectral lines from active nuclei in the cluster

   d. causes the cluster to glow all over as things fall into it

   e. makes the emission lines of the galaxies in the cluster shift wavelength significantly due to relativity

3. Gravitational lensing

   a. is being built in to the next generation of digital cameras

   b. produces peculiar arc-like images of galaxies at high redshift behind massive galaxy clusters 

   c. is useful for studying planets that pass in front of the sun

   d. was a surprise discovery not predicted by Einstein's theories of relativity

   e. changes the color of the objects lensed

4. The large-scale distribution of the galaxies in space is a result of

   a. the structure of the early Universe

    b. galaxies of similar types tending to clump together

    c. the gravitational attraction of great black holes that attract galaxies to their vicinity

    d. that galaxies tend to slow each other down when they pass closely, making them tend to concentrate together

    e. galaxies are fairly uniformly distributed, but intergalactic dust clouds hide aome of them and make the distribution look clumpy

5. Gravitational lenses in galaxy clusters are used

    a. to search for distant planets

    b. to study the theory of relativity

    c. to improve our determination of Hubble's Law

    d. to confirm that the clusters have huge amounts of dark matter

    e. to get a better view of the Big Bang

6. The central galaxies of dense clusters are

        a. similar to the other cluster members

        b. massive spirals that attracted the rest of the cluster galaxies around them

        c. virtually always with active nuclei because gas from the cluster is falling in

        d. massive ellipticals that result from many mergers with smaller cluster members

        e. galaxies with immense tidal tails and other indications of interactions