deletions | additions       diff --git a/The_Virgo_cluster_is_so__.tex b/The_Virgo_cluster_is_so__.tex  index 649274b..7a37a51 100644  --- a/The_Virgo_cluster_is_so__.tex  +++ b/The_Virgo_cluster_is_so__.tex 
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This technique works great for lightbulbs, but its a little trickier for stars and galaxies.  The biggest problem of course is that no two stars or galaxies are exactly alike, so you  don't always have a nearby reference point that is totally reliable.  Another issue, especially when using brightness scales, is that the Universe space  between source and telescope isn't empty, and the stuff in between distorts the image you see, biasing  your results. 
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Here's where we make our first whopping great assumption.   Why don't we assume that the Milky Way is perfectly typical?   I.e., let us assume that all the galaxies in Hydra I are just  like ours: they have radii of 10 15  kpc. So pick a bunch of galaxies in Hydra I and measure their diameters.   Some of them will be nearly edge-on, but that shouldn't stop