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George added subsection_Advanced_problems_Make_a__.tex
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\subsection{Advanced problems}
Make a map of Hydra 1. Get some overhead projector sheets and washable
marker pens. Put the transparent sheet on top of the Schmidt plate, and
mark the positions of the galaxies. You might like to use a colour code,
with different colours for spirals, ellipticals, and things just too darn
faint to decide. Don't bother mapping the edges of the plate \ -- \ concentrate
on the centre where the cluster is.
You can't possibly map every galaxy on the plate \ -- \ most are so
small you would need a microscope to tell them apart from the stars. So only
do the bigger ones, but try and be consistent; if you include smaller
galaxies in one part of the plate than another, it will introduce spurious
features into your map.
How big is the cluster (in Mpc, using your distance to the cluster)? How
many galaxies does it have? What fraction are spirals and ellipticals?
Do both types of galaxies live equally in all parts of the cluster? Is
the cluster nice and round, or is it distorted? If a cluster has distortions
and lumps, it tells you that it is a newly formed cluster, that has not
had time to settle down in equilibrium.
