deletions | additions       diff --git a/The_Virgo_cluster_is_so__.tex b/The_Virgo_cluster_is_so__.tex  index ede5f84..80945d8 100644  --- a/The_Virgo_cluster_is_so__.tex  +++ b/The_Virgo_cluster_is_so__.tex 
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it is a very difficult measurement.  Each student in the group should do their own measurements and you should compare the   results of each group member.  How might you go about improving your estimate? By far the worst feature of this calculation is the assumption that these  galaxies out in a distant cluster are just like our own galaxy.  
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One way is to be selective in our choice of galaxies to measure.   We know that our galaxy, the Milky Way, is a spiral galaxy.   So try measuring a distance using only spiral galaxies in Hydra I;  see the appendix section 2.4 below  for a description of different galaxy types. Has your answer changed? We also know that the Milky Way is one of  the largest spiral galaxies  in our the  local galaxy cluster. So group, so  perhaps it is similar to the largest spiral galaxies in Hydra I. Try getting a distance just from them. Even this doesn't necessarily help us very much: we've no good reason  to believe that even large spiral galaxies in Hydra I should be like  the Milky Way. A much better assumption would be that the galaxies in Hydra I are just like the galaxies in Virgo. After all, both clusters are about the same size, mass and density. It seems very plausible that the galaxies in Virgo should at least resemble those in Hydra 1. Here is a better method (using Virgo) to try and measure the distance to  Hydra I: