Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Calculating the luminosity density of the universe

  1. Mar 12, 2009 #1
    l = Phi*L*Gamma(a+2)


    The Sloan Digital Sky Survey (SDSS) has recently measured the following Schechter
    parameters in the r passband: a = -1.16 +/- 0.03, M*= -20.80 +/- 0.03, Phi* = (1.50 +/-0.13). Given that the sun has absolute magnitude M = 4.62 in the SDSS r band, calculate the luminosity density in this band in solar units. Estimate the error on this quantity.
    Gamma(0.84) = 1.122, Gamma(0.81) = 1.153, Gamma(0.87) = 1.094.

    I done the entire question and then realised i had made a grave error. And this is what I think it is; I took L* as being -20.80 +/- 0.03 ie M*, and im pretty sure this is wrong. Luminosity confuses me and I'm not sure how to relate the absolute magnitude M* to the Luminosity L*. I know that L* is supposed to be in the order of 10^10. Can anyone out there help? Its kind of urgent (due in tomorrow!).
  2. jcsd
  3. Mar 12, 2009 #2
    sorry i posted this in the wrong section. I've posted it again in the homework section. This can be deleted if need be.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook