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Unknown power?

  • 26-05-2009 7:34pm
    #1
    Kareir
    Closed Accounts Posts: 134 ✭✭


    Hey all,

    I was given this equation (distance to a star)

    D = 10^m-M+5/5

    where D is distance, m is apperant magnitude, M is absolute magnitude.

    A question gives the distance and M, but needs you to find the apperant mag.

    you end up with

    7.76=10^4.42+m/5, but how do you get the M out of the indices and down somewhere manageable. I was thinking Logs, so

    Log10(7.76)=Log10(10)^4.42+m/5

    Log10(7.76)=4.42+m/5, and so on


    But is this the right way to do it?

    Thanks,
    _Kar


Comments

  • #2
    MathsManiac
    Registered Users, Registered Users 2 Posts: 1,595 ✭✭✭MathsManiac


    Without brackets, that equation you gave is not as it should be.

    The correct equation is, I think: D = 10^[(m-M+5)/5]

    You can put the numbers in first and then rearrange, or you can rearrange first:

    log(D) = (m-M+5)/5 (log being to the base 10)
    5*log(D) = m-M+5
    5*log(D) + M - 5 = m.

    You should be ok from there.


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