Originally Posted by

**emmaastronomy** I have tried this but the answer i get is 2.5log10 (7.67x10*-5/5.3x10*-6) = 36.2. I know this is incorrect because i have already been given the answer which is 4.89. I am probably doing the calculation wrong but i am not sure, i have repeated it many times. Maybe i am putting it into the calculator wrong, but i doubt it. The question refers to the planets radii, is this unimportant? Thanks for the help so far, i'd have given up entirely otherwise.

My calculations give assuming the radius of Uranus is 1 (which we can do as we are working with ratios):

Code:

>F1=(0.5*2.5^2)/(9.5^2*8.5^2)
0.000479253
>F2=0.65/(19.2^2*18.2^2)
5.32314e-006
>
>
>2.5*log10(F1/F2)
4.88599
>

Also you have an error in your arithmetic, your result should be: 2.9 magnitude (the difference between this and the above is the approx. 2 magnitudes from my having forgotten the planetary radii (the way that you have written your answere suggests you handled the powers of 10 incorrectly)).

Reality check: Maximum brightness of Saturn 0.7 Mag, maximum brightness of Uranus 5.5 Mag.

CB