BrooklynVariety t1_j4lvkib wrote
Reply to comment by seriousnotshirley in How do we know that we are in a certain place inside our galaxy? and how do we know how big it is just by looking at the cross section we are in? by friday_panda
> With an estimate of the gravity of the center of the milky way we can estimate how from out the hydrogen we observe must be for it to be moving at the velocity that it does.
This would be a terrible way of doing this since you have know the geometry and mass distribution of the galaxy to have a model of how stars should be rotating. On top of that, even if you had a good model, you only measure line-of-sight velocities, making this pretty useless.
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