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Confusion with conversion for the Hubble Constant

  1. Feb 28, 2010 #1

    I want to get my data in terms of h70 -1

    Sometimes the estimates are in terms of h50 or h70, and I know how to convert those just fine.

    However, sometimes they give H0 = 100 h Mpc-1 kms-1 instead.....

    My question is, what is this in terms of h?

    I know that the relation is

    h = H0 / 100 kms-1 Mpc-1

    So, would I be right in thinking that it is as straight forward as h=H0 for this specific case or am I being silly

    Thankyou!! :)
  2. jcsd
  3. Mar 1, 2010 #2


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    :confused: Absolutely not, because as you yourself have noted, h is actually equal to:

  4. Mar 1, 2010 #3
    Hah. I totally figured it out.

    I was confused originally because I did use that equation, but got h=h

    I thought h=70, rather than H0 = 70


    So is 'h' basically just a fraction then? I understand now.

    Gah. Thanks
  5. Mar 2, 2010 #4


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    Which is true! But not that informative I guess.

    Right, so that's where your misconception was. That value of H0 corresponds to h = 0.7

    Exactly, you got it now! The parameter h is a dimensionless version of the Hubble constant. It is H0 normalized to a reference value of 100 km s-1 Mpc-1. So h is a fraction...it tells you the ratio of H0 to that reference value.
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