deletions | additions       diff --git a/Find_the_average_vel.tex b/Find_the_average_vel.tex  index 218ce00..7dce019 100644  --- a/Find_the_average_vel.tex  +++ b/Find_the_average_vel.tex 
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Find the average velocity with which Hydra I is running away from us  (why don't all the galaxies in Hydra I have the same velocity?) Use  the average velocity to find Hubble's constant. What value do you get? Express  $H_0$is  traditionally expressed  in units of kilometres per second per Megaparsec. The debate over the true value Measurements  of Hubble's constant is without have  a doubt  the longest long  and bitterest in the recent history of astronomy. For a  racy account of the ``Hubble Wars'' read `Lonely Hearts of the  Universe' by Dennis Overbye, controversial history,  and several recent articles for a long time different groups using different methods to measure $H_0$  obtained widely discrepant results.  Fortunately, things have settled down  in New  Scientist recent years,  and Scientific American. One group of researchers, prominent  amongst whom is Alan Sandage of California, regularly find low values,  one of their latest being $H_0 = 42\ {\rm km}s^{-1}{\rm  Mpc}^{-1}$. Another group, including Jeremy Mould (until just recently  director of Mt Stromlo Observatory near Canberra) keep finding higher  values, around $H_0 = 80\ {\rm km}s^{-1}{\rm Mpc}^{-1}$. The the  most recent Hubble Space Telescope result was results from  ESA's Planck satellite give  $H_0 = 68 67.8  \pm 6\ {\rm  km}s^{-1}{\rm Mpc}^{-1}$. Who do you agree with? 0.9$ km/s/Mpc, which is mostly   consistent with other measurements.  If your result is not near any of these, different from this,  take heart, Edwin Hubble's first measurement was $H_0 > 400\ {\rm km}s^{-1}{\rm Mpc}^{-1}$!  \subsection{Age of the Universe}